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Enhanced Weathering in Agriculture
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This Protocol provides the requirements and procedures for the calculation of net carbon dioxide equivalent (CO2e)removalRemoval from the atmosphere via enhancedEnhanced weatheringWeathering (EW) in agricultural settings. Agricultural EW is considered a subcategory of EW approaches.
Silicate weathering naturally sequesters approximately 0.1-0.3 Gt of CO2 per year1, 2,3 and is thus a critical feedback mechanism in global climate regulation on geologic timescales. In this process, atmospheric CO2 dissolved in surface water reacts with silicate rocks and is converted to dissolved inorganic carbon or carbonate minerals, both of which constitute stable sinks for CO2 on geologic timescales4, 5. Natural weathering can be accelerated by applying crushed silicate rock to agricultural land, where the increased reactive surface area of the rock and damp conditions in the soil lead to elevated reaction rates. Alkaline species produced through weathering reactions allow for the increased storage of CO2 in the aqueous phase, typically as dissolved bicarbonate. This dissolved inorganic carbon is eventually exported to the ocean where it can be stably stored for millennia 6. This process is known as enhanced weathering and has been proposed as an effective natural Carbon Dioxide Removal (CDR) technique, in accordance with the Intergovernmental Panel on Climate Change (IPCC)7, to mitigate potential impacts of anthropogenic climate change8. Given that cropland covers approximately 38% of land surface on Earth, EW in agricultural settings has large scalability potential with relatively small changes in farm management. Scalability is aided by existing infrastructure of rock spreading as a soil amendment. Current estimates suggest that EW in cropland has the capacity to remove on the order of 1-2 Gt of CO2 per year8. In addition to CO2 removal, EW can potentially provide co-benefits to farmers in the form of increased crop yield and resiliency9, 10, as well as replenishment of soil nutrients11, 12 and reduction of nitrogen loss9, 13.
This Protocol accounts for the quantification of the gross amount of CO2 removed via agricultural EW, as well as all cradle-to-grave, life-cycleGreenhouse Gas (GHG) emissions associated with the process.
This Protocol is developed to adhere to the requirements of ISO 14064-2: 2019 -- Greenhouse Gases -- Part 2: Specification with guidance at the project level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements. The Protocol ensures:
In addition to CO2 removal, dissolution of silicate rocks in agricultural settings may provide co-benefits through the addition of nutrients, alkalinity and silica in soils. Potential co-benefits include:
Increased soil nutrients and crop resilience by EW can lead to increased yields, which may help to alleviate global food insecurity if deployed at scale. EW also has the potential to further mitigate emissions via reduction of nitrous oxide fluxes in cropland, which is currently thought to represent 50-80% of global anthropogenic N2O emissions13.
This protocol mainly utilizes and is intended to be compliant with the following standardsStandards and protocols:
Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:
Additional standards, methodologies and protocols that were reviewed, referenced or for which attempts were made to align with or leverage during development of this Protocol include:
This Protocol was developed based on the current state of the art, publicly available science regarding EW in agriculture. Because EW is a novel CDR approach, with limited published literature, this Protocol incorporates requirements that may be more stringent than some current relevant regulations or other protocols related to EW for CDR.
Future versions of this Protocol may be altered, particularly regarding requirements for demonstrating durabilityDurability of EW, as the stability of CO2 captured by EW from feedstockFeedstock dissolution in agricultural soils becomesis wellbetter demonstrated and documented; reversalReversal risks are proven to be limited; and the overall body of knowledge and data regarding all processes, from feedstock supply to conversion and to permanent storage, is significantly increased.
This Protocol applies to projects or processes which:
utilizeUtilize crushed rock or mineral feedstock applied to agricultural land to capture CO2
rockRock or mineral feedstock is defined as silicate rock containing alkaline earth and alkali metals (i.e. Ca, Mg, K, and Na), which converts CO2 to aqueous bicarbonate when applied in sufficient quantities to agricultural land to convert CO2 to aqueous bicarbonate
This Protocol applies to projects and associated operations that meet all of the following project conditions:
Projects that are explicitly NOT eligible include the following:
As previously stated, per the UN FAO definition of permanent and arable crop land, meadows and pastureland are eligible for EW projects. This Protocol will refer to monitoring requirements specific to row cropland, such as monitoring crop yield, health, and resiliency. Such measurements may not be applicable to projects taking place on pastureland and therefore may not be required in the Project Design Document (PDD). Justifications to omit measurements in such instances are allowable in the PDD.
The Project must consider environmental and social impacts at all projectProject locations, including the quarryingmine andor deploymentquarry siteswhere andfeedstock is sourced, during feedstock transportation, and at the deployment site. Appropriate measures must be implemented to identify and eliminate potential risks to terrestrial and aquatic ecosystems and biodiversity. Where risks cannot be eliminated, the PDD must identify measures to monitor ecosystem health and mitigate adverse effects through a project-specific mitigation plan. Mitigation plans must be carried out by subject matter experts, in consultation with Isometric. Refer to Section 3.7 of the Isometric Standard for further guidelines on environmental and social impacts.
Creditsissued under Isometric's Enhanced Weatheringthis Protocol are contingent on the implementation, transparent reporting and independent verification of comprehensive safeguards. These safeguards encompass a wide range of considerations, including environmental protection, social equity, community engagement and respect for cultural values. The process mandates that safeguard plans be incorporated into all major project phases, with detailed reports made accessible to stakeholders. Adherence to and verification of environmental and social safeguards, in accordance with Section 3.7 of the Isometric Standard, is a condition for all crediting projects.
Ongoing environmental assessment must be completed in accordance with the Isometric Standard to identify potential risks, followed by the development of tailored mitigation plans by subject matter experts where necessary. Project Proponents must first strive to avoid negative environmental impacts. In cases where adverse environmental effects take place, the Project Proponent must develop plans to minimize and rectify them. For example, this could include measures such as employing pollution control technologies. Effective implementation of these measures must also be accompanied by a robust monitoring plan to ensure efficacy. Project Proponents must demonstrate active stakeholder engagement throughout this process, in accordance with Section 3.5 of the Isometric Standard. All mitigation strategies must align with local and international environmental laws and contribute to sustainable project outcomes.
Enhanced Weathering of rock or mineral feedstock may be associated with the release of metals such as nickel (Ni) and chromium (Cr) or other harmful contaminants such as asbestiform minerals, which may pose an environmental risk. To prevent or mitigate such risks, the Project Proponent must take the following measures:
The Project Proponent must carefully consider and implement measures where necessary for the following potential impact areas before proceeding with an EW project. Appropriate measures must be implemented to identify and eliminate potential risks to human health and cultural rights at all project locations.
Maintaining agricultural productivity is critical to the environmental and social sustainability of EW projects. The Project Proponent must document how the project will monitor agricultural productivity and soil quality, including which productivity and soil characteristics will be tested and the frequency of testing. If justified, the Project Proponent may use proxy variables in lieu of direct testing or measurement. If productivity or soil quality are demonstrated or anticipated to be adversely affected, the Project Proponent must complete the following:
All environmental and social safeguards will be verified to be implemented at all locations in the EW process, including at the feedstock source, transportation, and distribution sites. The Project Proponent must regularly assess the combined environmental impact of EW, which includesmay include (but is not limited to) heavy metal concentrations in crops and groundwater. This may involve collecting data on soil and water quality, biodiversity indicators and agricultural productivity. The cadence of monitoring will vary based on the parameter. Accumulation of heavy metals in soils and crops must be assessed at a minimum of once per Reporting Period. Aqueous measurements will depend on the local water budget, but should be assessed quarterly at a minimum. All data indicators, data collection protocols and data interpretation must be writtendeveloped or performed by subject matter experts. The Project Proponent must use the collected data to inform ongoing management of EW practices. This data must be shared with the public through Isometric's platform, in accordance with Section 6.6 of this Protocol. The Project Proponent must be prepared to adjust the EW strategy based on monitoring results and feedback from environmental studies and community engagement.
The following topics are covered briefly in this Protocol due to their inclusion in the Isometric Standard, which governs all Isometric Protocols. See in-text references to the Isometric Standard for further guidance.
For each specific projectProject to be evaluated under this Protocol, the Project Proponent must document Project characteristics in a Project Design Document (PDD) as outlined in Section 3.2 of the Isometric Standard. The PDD will form the basis for project verification and evaluation in accordance with this Protocol, and must include consideration of processes unique to each agricultural EW project, such as:
Projects must be validated and projectthe Project GHG Statement (net CO2e removal) verified by an independent third party consistent with the requirements described in this Protocol as well as in Section 4 of the Isometric Standard.
The Validation and Verification Body (VVB) must consider following requisite components:
The threshold for Materiality, considering the totality of all omissions, errors and mis-statements, is 5%, in accordance with Section 4.3 of the Isometric Standard.
Verifiers should also verify the documentation of uncertainty of the GHG Statement as required by Section 2.5.7 of the Isometric Standard. Qualitative Materiality issues may also be identified and documented, such as21:
Project validationValidation and verificationVerification must incorporate site visits to project facilities, namely agricultural fields being used as control, treatment and deployment plots, in accordance with the requirements of ISO 14064-3, 6.1.4.2. This is to include, at a minimum, site visits during validation and initial verification to the project site(s). Validators should, whenever possible, observe project operation to ensure full documentation of process inputs and outputs through visual observation.
A site visit must occur at least once every 2 years atduring each controlproject validation. Additional site visits may be required if there are substantial changes to field operations over the course of a project's validation period, treatmentor andif deploymentdeemed plotnecessary by Isometric or the VVB.
Verifiers and validators must comply with the requirements defined in Section 4 of the Isometric Standard. In addition, teams shall maintain and demonstrate expertise associated with the specific technologies of interest, including soil sampling, analysis and data processing.
CDR via EW in agriculture is often a result of a multi-step process (such as quarrying, transporting and spreading of rock), with activities in each step potentially managed and operatedperformed by a different operator, company or owner. When there are multiple parties involved in the process, and to avoid double counting of CO2e removals, a single Project Proponent must be specified contractually as the sole owner of the Credits. Contracts must comply with all requirements defined in Section 3.1 of the Isometric Standard.
The GHG Removal Project Proponent shallmust be able to demonstrate additionality through compliance with Section 2.5.3 of the Isometric Standard. The baselineBaseline scenarios and counterfactualCounterfactual utilized to assess additionality must be project-specific, and are described in Sections 7 and 9 of this Protocol.
Additionality determinations shouldmust be reviewed and completed at the time of initial verificationVerification oras wheneverwell as following significant changes to project operating conditions change significantly, suchincluding asbut thenot followinglimited to:
project financialsfinance indicate Carbon Finance is no longer required, potentially due to, for example:
increased tipping fees for waste feedstocks
Any review and change in the determination of additionality shall not affect the availability of Carbon Finance and Carbon Credits for the current or past Crediting Periods, however, if the review indicates the Project has become non-additional, this shall make the Project ineligible for future Credits22.
The uncertainty in the overall estimate of the net CO2e removal as a result of the Project must be accounted for. The total net CO2e removed for a specific Reporting Period, [math: RP], CO2eRemoval, RP, must be conservatively determined in accordance with the requirements outlined in Section 2.5.7 of the Isometric Standard.
Projects must report a list of all input variables used in the net CO2e removal calculation and their uncertainties, including:
More detailed uncertainty information should be provided if available, as outlined in Section 2.5.7 of the Isometric Standard. Uncertainty must be quantified at the project scale, which may include multiple fields within a region.
In addition, a sensitivity analysis that demonstrates the impact of each input parameter's uncertainty on the overall net CO2e removal uncertainty must be provided. Details of the sensitivity analysis method must be provided so that the results canare be re-createdreproducible. Input variables may be omitted if they contribute to a < 1% change in the net CO2e removal.
In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of CO₂e removal and environmental and social safeguards monitoring will be available to the public through Isometric's platform. That includes:
The Project Proponent can request certain information to be restricted (only available to authorized Buyers, the Registry and VVB) where it is subject to confidentiality. This includes emissions factors from licensed databases. However, all other numerical data produced or used as part of the quantification of net CO₂e removal will be made available.
The scope of this Protocol includes GHG sources, sinks and reservoirs (SSRs) associated with an EW CDR project. A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary (Figure 1).
Emissions for processes within the system boundary must include all GHG SSRs from the construction or manufacturing of any project-specific physical site and associated equipment; closure and disposal of each site and associated equipment; and operation of each process (including feedstock production, transport, spreading and sampling for MRV) to include embodied emissions of consumables in the process.
Any emissions from sub-processes or process changes that would not have taken place without the CDR project, such as subsequent transportation and refining, must be fully considered in the system boundary. Paired with exclusion of waste input emissions when the criteria are met (see Section 7.1.1), this allows for accurate consideration of additional, incremental emissions induced by the CDR process.
The system boundary must include all SSRs controlled by and related to the project, including but not limited to the SSRs in Figure 1 and Table 1. If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence is provided.
Figure 1. Process flow diagram showing system boundary for EW projects [Image: Figure 1]
Table 1. Systems boundary and scope of activities to be included for EW projects
| Activity | GHG source, sink or reservoir | GHG | Scope | Timescale of emissions and accounting allocation |
|---|---|---|---|---|
| Establishment of project | Quarrying | All GHGs | Quarrying activities including the following emissions sources:
| Before Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 7.4.3.1) |
| Transport to crushing site | All GHGs | Transporting the feedstock material from the excavation site to the crushing facility | ||
| Crushing and grinding (including additional processing steps such as drying) | All GHGs | Crushing and grinding activities including the following emissions sources:
| ||
| Feedstock transport to application site | All GHGs | Transporting the feedstock material from the quarrying site to the agricultural application site | ||
| Feedstock characterization | All GHGs | Embodied, energy use and transport emissions associated with sampling the feedstock to measure the physical and geochemical characteristics necessary for weathering determinations | ||
| Spreading on agricultural application site | All GHGs | Spreading activities including:
| ||
| Misc. | All GHGs | Any GHG SSR not captured by categories above, for example related to field surveys | ||
| Operation | Sampling and analysis | All GHGs | Sampling and analysis activities, including:
| Over each Reporting Period - must be accounted for in the relevant Reporting Period (See Section 7.4.3.2) |
| CO2 stored | CO₂ | The gross amount of CO2 removed and durably stored from an EW project over a Reporting Period | ||
| Misc. | All GHGs | Any GHG SSR not captured by categories above, for example related to refrigeration for storing soil cores | ||
| End-of-Life | Misc. | All GHGs | Activities post-Reporting Period, for example end-of-life emissions associated with equipment or deconstructing infrastructure | After Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 7.4.4.3) |
The Project Proponent must consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s definition of GHGs, which includes: carbon dioxide (CO₂), methane (CH4), nitrous oxide (N2O) and fluorinated gasses such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3). For CO2 stored, only CO2 shallwill be included as part of the quantification. For all other activities all GHGs must be considered. For example, the release of CO2, CH4, and N2O is expected during diesel consumption.
All GHGs must be quantified and converted to CO2e in the GHG Statement using the 100-yr Global Warming Potential (GWP) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report).
Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSR categories provided in Table 1. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities and must report any outside of the SSR categories identified as miscellaneous emissions.
Emissions associated with a project's impact on activities that fall outside of the system boundary of a project must also be considered. This is covered under Leakage in Section 7.4.3.4.
The following are excluded from system boundaries:
Ancillary activities (such as supplementary research and development activities and corporate administrative activities) that are associated with a project but are not directly or indirectly related to the issuance of Credits can be excluded from the system boundary.
EW may have additional impacts on GHG emissions beyond the scope of this Protocol. For example, there is some evidence that EW in agriculture may have secondary impacts on N2O and CH4 emissions associated with agricultural soils. These potential impacts are not currently included in the conservative GHG accounting framework and will be reviewed as scientific consensus evolves.
Similarly, emissions reductions associated with other processes that could arise as a result of the EW project should not be credited toward the project.
Embodied emissions associated with system inputs considered asto be waste products can be excluded from the accounting of the GHG Statement system boundary ofprovided the CDRappropriate process if all of the beloweligibility criteria are met:.
If EC1 in Table 2 is satisfied, embodied emissions associated with the waste product isinput fundamentallycan tiedbe excluded from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary, as compliance with EC1 would result in no change to or is the resultwaste ofproducer abehavior separate(i.e. process.
Table 2. Waste input emissions exclusion criteria, EC1
| Criteria | Description | Documentation required |
|---|---|---|
| EC1 | No payment was made for the material, or only a “tipping fee” is paid. | Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, buyer, seller and date. Additionally, a signed affidavit from the Project Proponent stating that no in-kind compensation was made to the feedstock supplier must be provided. |
If EC2 and EC3 in Table 3 are both satisfied, embodied emissions associated with the waste product input can be excluded from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary, as compliance with EC2 and EC3 would result in no significant change to the waste producer behavior (i.e. no market leakage) and there are no alternative use cases for the waste product (i.e. no replacement emissions).
Table 3. Waste input emissions exclusion criteria, EC2 and EC3
Criteria | Description | Documentation required |
|---|---|---|
EC2 | The amount of the waste product used by the CDR project was not already being utilized as a valuable
| Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, buyer, seller and date. |
EC3 | Payments for the waste product | Feedstock |
In some instances, the EW project activities may be integrated into existing activities, such as rock spreading whilst seeding. Activities that were already occurring and would continue to occur without the EW project may be omitted from the system boundary of the GHG accounting, if evidence that the activity was already occurring and would have continued to occur in the absence of the EW project can be provided.
The baseline scenario for EW projects assumes the activities associated with the EW project do not take place, no new infrastructure is built and business as usual agricultural practices occur.
The counterfactual is the CO2 that would have been removed from the atmosphere and durably stored as a result of natural weathering or pre-existing land practices. This is determined through the use of a control plot, as descibeddescribed in Section 7.4.2, with detail on monitoring requirements described in Section 9.3.4.3.
EW in agriculture typically consists of an application of a characterized rock or mineral feedstock followed by discrete sampling periods to quantify CO2 removals. Rock or mineral feedstock must be sourced, which may include quarrying, processing (e.g., crushing) and transportation, before it is spread over agricultural land. A combination of soil, aqueous and aqueousother geochemical measurements are then used to quantify the total CO2 removals over a period of time.
The Reporting Period for EW represents an interval of time over which removals are calculated and reported for verification. Monitoring of CO2 removals for EW may include a combination of discrete sampling (e.g., soil sampling) and continuous sampling. The equations used to calculate net CO2e removals will pertain to all GHG emissions and CO2 removals occurring over a Reporting Period. In most cases, this Reporting Period will be an interval of time bounded by sampling events.
GHG emission calculations must include all emissions related to the project activities that occur within the Reporting Period. This includes: a) any emissions associated with project establishment allocated to the Reporting Period, b) any emissions that occur within the Reporting Period, c) any anticipated emissions that would occur after the Reporting Period that have been allocated to the Reporting Period and d) leakage emissions that occur outside of the project boundary as a result of induced market changes that are associated with the Reporting Period. Requirements for allocated emissions to Reporting Periods are set out in Section 7.4.3. All allocated emissions must must be accounted for by the Reporting Period in which 50% of total feedstock weathering potential has been realized.
Total net CO2e removal is calculated for each Reporting Period, and is written hereafter as [math: {{CO}_{2}^{}e}_{Removal,\ RP}].
Net CO2e removal for EW in agriculture for each Reporting Period, [math: RP], can be calculated as follows. The final net CO2e removal quantification must be conservatively determined, giving high confidence that at a minimum, the estimated amount of CO2e was removed (refer to Section 6.5 for details).
[math: {CO}_{2}^{}e_{Removal,\ RP}^{}\ = \ {CO}_{2}^{}e_{Stored,\ RP}^{}\ –\ {CO}_{2}^{}e_{Counterfactual,\ RP}^{}–\ {CO}_{2}^{}e_{ Emissions,\ RP}^{}]
(Equation 1)
Where:
Note: Reversals occur after Credits have been issued so are not included in this equation. See Section 9.2 and Section 5.6 of the Isometric Standard for further information.
Type: Ocean storage
The total amount of CO2 stored from an EW project must include the following terms:
[math: {CO}_{2}^{}e_{Stored,\ RP}^{}\ = \ \sum_{}^{}{CO}_{2}e_{Drawdown,\ RP} - \sum_{}^{}{CO}_{2}e_{Losses,\ RP}]
(Equation 2)
Where:
This quantification framework considers the terms given in Equation 2 relative to two distinct zones, referred to as the Near-Field Zone (NFZ) and the Far-Field Zone (FFZ). The NFZ represents the portion of the upper soil column in which the weathering reaction and subsequent processes (e.g. soil and biomass uptake, secondary mineral formation) must be directly tracked and, for practical purposes, is defined as the depth of deepest soil sampling. The FFZ is defined as the transport path for the weathering products from the boundary of the NFZ to the final storage reservoir (typically the ocean). This includes the deep soil column, groundwater network, riverine transport and ocean discharge.
In this mass/charge balance approach, we explicitly account for both: 1) permanent losses of base cations (and corresponding CO2 removals) that happen after base cations are released from a rock or mineral feedstock through weathering and 2) the possibility that base cations may be temporarily, but not permanently, rendered ineffective for removals. These include both permanent and temporary losses.
Losses considered to be permanent include:
Losses considered to be temporary include:
One particularly consequential aspect of these CO2 removal loss terms is the potential time lag associated with cation sorption. A base cation may undergo many generations of sorption and desorption to cation exchange sites while migrating through the soil column, delaying the CO2 removal effect until that cation is sufficiently deep in the soil column or more permanently transitions to the aqueous phase. There is currently no widely held scientific consensus on the best practices for modeling these cation sorption dynamics.
The sorption of base cations to cation exchange sites will cause re-equilibration of dissolved inorganic carbon species to maintain charge balance, which will result in degassing of CO2 into soil pore space. If this degassing occurs sufficiently deep in the soil column, the resulting transient CO2 may be sufficiently isolated from the atmosphere as to be considered a removal while the cation is still migrating through the soil column.
HereThis weProtocol makedefines removal relative to the simplifyingprimary assumptionquantification thatmedium once(e.g. solid or aqueous measurements). Where soil is used for CDR quantification, this Protocol considers removal to have occurred when base cations passare throughexported from the depth of deepest soil sampling, they can effectively be considered a removalNFZ. This Protocol currently recommends thisthe depth of the NFZ to be atthe minimumdeeper 30of
A shallower windowdefinition of directthe soil observationsNFZ may be used in circumstances where 30meeting centimetersthese criteria is not feasible (e.g., shallow water table occurs at a depth less than 30 centimeters, or 30 cmwhich cannot be accessed through conventional sampling methods). Such deviations must be reported and justified in the PDD. Where aqueous phase measurements are used for quantification, base cations can be credited within the NFZ once they have entered the porewater.
All crediting projects must design a sampling plan that directly measures the initial weathering of rock or mineral feedstock through soil and porewater sampling. Once a statistically significant amount of feedstock weathering has occurred, the Project Proponent may be eligible for Credits. This Protocol currently allows for two separateprimary determinationsquantification ofapproaches for determining the the carbon stored from an EW project: 1) fromsoil-based a combination of soil and porewater measurementsquantification and 2) fromporewater-based porewater measurementsquantification. ShouldAdditionally, this Protocol currently requires validation of the Projectcredit Proponentquantification choosethrough toa measuresecondary realizedmedium. CO2For removalexample, fromwhere bothsoil-based determinationsmeasurements are used for research purposesquantification, theaqueous phase measurements are used for validation. The determination used for crediting and for validation must be designated in the PDD. IfThe Determinationdetails 2of isquantification usedrequirements forare crediting,addressed aqueous phase measurements must be conducted on samples collected fromin the depthfollowing of deepest soil sampling in Determination 1 (i.e., 30 centimeters)sections.
There are multiple approaches to quantifying enhanced weathering that have been employed in scientific studies and early enhanced weathering deployments. These methods currently fall into two major categories, solid phase measurements and aqueous phase measurements. Solid phase measurements quantify the loss of base cations from feedstock-amended soil over time, while aqueous phase measurements quantify the accumulation of base cations in soil pore water. In addition to these approaches, there are a number of other technologies at various stages of development that may prove useful for quantifying enhanced weathering in an agriculture setting (e.g., reactive transport models, ion exchange resin). The Isometric science team will regularly assess the state of scientific consensus around new and emerging technologies for application to measuring CDR via enhanced weathering.
This Protocol includes a list of quantification approaches that can be used to determine the amount of carbon stored. In addition to quantification approaches, this Protocol also includes a list of allowable validation approaches that may be used by crediting projects.
All projects seeking credits must quantify the amount of carbon stored using one of the listed quantification approaches in List 1. The quantification approach must be conducted within the framework of an appropriate sampling framework, as discussed in Section 9.3 (e.g., 2-plot, 3-plot). Additionally, the Project Proponent must select and implement at least one validation approach, listed in List 2. This validation is meant to be a localized, independent sense check on the quantification approach. The validation approach must be conducted within both a treatment and control area that represents at least 2.5% of the Project area. The same approach cannot be used for both quantification and validation.
The quantification and validation approaches currently accepted for crediting projects are:
List 1: Quantification Approaches
List 2: Validation Approaches
The mean value from the validation method (List 2) must be within the 99.7% confidence interval of the quantification approach. If this is not the case, Projects must conduct an audit and work in consultation with the Isometric science team to surface an explanation for this discrepancy.
A previous version of this Protocol used the terms Determination 1 to describe soil-based quantification with porewater-based validation and Determination 2 to describe powerwater-based quantification with soil-based validation. These terms are no longer used in favor of the more flexible and forward-looking framework described here.
It is anticipated that new technologies and methods for quantifying and validating enhanced weathering in agriculture will emerge in the coming years. These new technologies will be regularly assessed by the Isometric science team for inclusion in this Protocol. New technologies and methods that have some demonstrated efficacy when compared to conventional soil and porewater approaches will be included in List 2 and may be used as a validation approach. New technologies and methods that have demonstrated efficacy and have gathered wide scientific consensus will be included in both Lists 1 and 2 (may be used for either quantification or validation).
Particularly, we anticipate that reactive transport models or other suitable models, which are currently insufficient for predicting enhanced weathering rates, will improve significantly in the coming years from large amounts of calibration data. Isometric will continue to evaluate reactive transport models for inclusion in Lists 1 and 2 in future iterations of this Protocol.
Formerly part of Determination 1
The total amount of carbon stored from an EW project can be determined from soil and porewater measurements according to:
[math: {CO}_{2}^{}e_{Stored,\ RP}^{} = {CO}_{2}^{}e_{Weathering, RP}^{} - {CO}_{2}^{}e_{BiomassLoss,\ RP}^{} - {CO}_{2}^{}e_{NetNewCarbonate,\ RP}^{} \\ - {CO}_{2}^{}e_{NetNewSilicate,\ RP}^{}- {CO}_{2}^{}e_{NetSorption,\ RP}^{} - {CO}_{2}^{}e_{NonCarbonicNeut, RP}^{} \\ - {CO}_{2}^{}e_{RiverineLoss,\ RP}^{} - {CO}_{2}^{}e_{MarineLoss,\ RP}^{}]
(Equation 3)
Where:
All terms have units of tonne CO2e.
Below is an overview of how each term is determined, with more details provided in Section 9.
[math: {CO}_{2}^{}e_{Weathering,\ RP}^{}] must be determined from direct geochemical observation of soilthe in deploymentproject area per Section 9.3.4. A depth of 30 cm is chosen because common tilling depths are unlikely to exceed 30 cm, and 30 cm has become widely used in the EW community to assess feedstock weathering rates. If tillage depth exceeds 30 cm, the minimum sampling depth must be increased to a depth greater than the tillage depth. In such instances, tillage and sampling depth must be reported in the PDD. Shallower sampling may be acceptable for the determination of feedstock weathering if it can be justified based on field management practices and observed depth of feedstock tracer in soil. While shallower sampling is acceptable for determination of initial weathering, 30 cm sample depths should still be used for soil based measurements outlined below (unless alternative sampling depth is justified in PDD). Nearly all emerging soil-based methods for determining in-field [math: {CO}_{2}^{}e_{Weathering,\ RP}^{}] rely on measuring the abundance of some insoluble elemental or isotopic tracer and its ratio to soluble base cations in the feedstock to determine weathering. This includes measuring the abundance of both insoluble tracer(s) and soluble base cations before and after feedstock application to determine the weathering potential, and measuring the evolution of these two groups of analytes at later time points to determine the gross CO2 removal before accounting for the various losses. TheProject changeProponents inusing thesoil-based chosenmeasurements tracer(s)for of base cation releasequantification must showdemonstrate differences that area statistically significant loss of cations between the start and the end of the Reporting Period to be eligible for crediting (see Section 9.3.4.2.1). The projectProject must clearly specify all of the following in the PDD:
Once the statistical criteria for crediting have been met (see Section 9.3.4.2.1), [math: {CO}_{2}^{}e_{Weathering,\ RP}^{}] for the area of interest (may be a treatment or deployment plot if 3-plot approach is used) should be determined by calculating the total CO2 removal in the treatment and deployment areas separately before adding them together. In soils, this will take the following form:
[math: {CO}_{2}^{}e_{Weathering,\ RP,\ x}^{} = \ - \Delta{\lbrack ALK\rbrack}_{x} \times \rho_{x} \times d_{x} \times A_{x} \times \frac{CDR}{ALK}]
(Equation 4)
Where:
Additional details on soil based field monitoring are included in Section 9.3.4.
[math: {CO}_{2}^{}e_{BiomassLoss,\ RP}^{}] is determined from direct, representative sampling of plant tissues atof peakharvested biomass (annual crops) or new plant growth (perennial crops) in an area in which feedstock is applied (treatment area if using 3-plot approach) and the control plotsplot. (thisThis does not need to be directly measured in the deployment plot if using 3-plot approach). Sampling routines must be identical between areas with and without feedstock. Plant samples must be analyzed for C, N, Na, K, Mg and Ca concentrations (base cations not used for crediting may be omitted from this measurement). Project Proponents are required to cross reference the following standards for their measurement procedures:
For cation measurements, Project Proponents are required to outline and justify their method for digestion (dissolving sample into liquid phase) of plant material in the PDD.
Sampling plans targeting plant uptake must consider the total amount of new biomass produced over the Reporting Period and the crop type (annual vs. perennial). Project Proponents are required to include all data and calculations in submitted reports, including information on standards and calibration curves. This data shouldwill likely include total shoot mass, total plant mass and cation concentrations.
The Project Proponent must describe in the PDD how measurements of base cations removed by plant uptake are conservatively extrapolated over the project area for the determination of [math: {CO}_{2}^{}e_{BiomassLoss,\ RP}^{}].
[math: {CO}_{2}^{}e_{NetNewCarbonate,\ RP}^{}] represents the average net change in soil inorganic carbon (SIC) between the start and the end of the Reporting Period. This measurement pertains to all soils collected in the observation windowNFZ, typically 0 to 3020 cm, but should also proportionally represent sample fractions if samples are partitioned for determination of initial weathering (e.g., total SIC is determined from a weighted average of 0-10 cm samples and 10-3020 cm samples). This Protocol requires that SIC, when measured, is measured via either calcimetry or thermo-gravimetric analysis. This must be quantified using:
We note that some methods for measuring enhanced weathering in soils (e.g., total acid digestion followed by bulk cation quantification) implicitly include SIC monitoring; this is generally acceptable under this Protocol.
Project Proponents utilizing other determinationcarbonate quantification methods, in consultation with Isometric, must outline and justify these alternative analyses in the PDD.
This value of [math: {CO}_{2}^{}e_{NetNewCarbonate,\ RP}^{}] may be positive, zero or negative. A positive value corresponds to a net increase in soil inorganic carbon, which will result in less CO2 being stored. A negative value corresponds to net dissolution of carbonate minerals, and may lead to net CO2e removal if dissolution is the result of reaction with carbonic acid.
Soil inorganic carbon is typically determined in weight percent (e.g., kg calcium carbonate per kg soil). The corresponding amount of CO2 stored in net new carbonate is determined as follows:
[math: {CO}_{2}^{}e_{CaCO_{3},\ t}^{}\ = (wt\%\ {CaCO}_{3}) \times (\frac{1}{100}) \times (0.44) \times \rho_{x} \times d_{x} \times A_{x} \times (\frac{1\ ton}{1000\ kg})]
(Equation 5)
[math: {CO}_{2}^{}e_{NetNewCarbonate,\ RP}^{} = \ {CO}_{2}^{}e_{CaCO_{3},\ \ t = 2}^{} - {CO}_{2}^{}e_{CaCO_{3},\ \ t = 1}^{}]
(Equation 6)
Where:
Some project areas may have soil conditions where carbonate precipitation is not likely and not observed above analytical detection limits (e.g., low pH soils). Project Proponents operating in such areas may omit large scale soil inorganic carbonate measurements from routine monitoring with adequate justification in the PDD. In such instances, Project Proponents must conduct smaller scale measurements of soil inorganic carbon with each major sampling event to demonstrate that these assumptions still hold. If local geochemical conditions change over the course of a project and lead to measurable soil carbonate mineral accumulation, soil inorganic carbonate measurements must be reinstated at the same density as other primary soil measurements.
[math: {CO}_{2}^{}e_{NetNewSilicate,\ RP}^{}] is the average net change in silicate mineral (e.g., clay mineral) content between the start and end of the Reporting Period. There is no widely accepted and operationally feasible quantitative method for determining modest changes in secondary silicate mineral content in soils; clay content of soils is typically expressed as a percentage of clay-sized particles, and mineralogy is determined by xX-ray diffraction. Thus, detection of new secondary clay formationclays requires either significant enough clay formation to shift the percentage of clay-sized particles in the soil column or quantitative formation of clay mineralogies that are distinct from the initial assemblage (unlikely for modest pH change in soils with similar moisture retention; see Wilson (1999)25 for an overview of the parameters controlling clay formation in soil)25. WeThis haveterm is included this term for completeness,; but weIsometric will not explicitly require measurement of this parameter at this time.
[math: {CO}_{2}^{}e_{NetSorption,\ RP}^{}] is determined by measuring any change in adsorbed base cations in the NFZ over the Reporting Period. Typically, this is determined using the difference in the product of cation exchange capacity and base cation saturation between the start and end of the Reporting Period. A positive value corresponds to a net increase in base cations sorbed to cation exchange sites, leading to outgassing of dissolved CO2. Conversely, a negative value corresponds to a net decrease in base cations sorbed, leading to CO2 removal. Cation exchange capacity measurements should comply with ISO 11260:2018, ISO 23470:2018 or the Chapman method. Quantification of base saturation should comply with ISO 11260:2018. Some agronomic soil testing facilities may use regionally specific methodologies that deviate from the standards listed above. Such methodologies are generally permissible, but require approval by Isometric. Such alternative methods must be approved by Isometric and justifiedjustification in the PDD.
We note that some methods for measuring enhanced weathering in soils (e.g., total acid digestion followed by bulk cation quantification) implicitly include net sorption monitoring; this is generally acceptable under this Protocol.
[math: {CO}_{2}^{}e_{NonCarbonicNeut,\ RP}^{}] may be determined using direct measurements of anions in porewaters, an approximation based on soil pH and pCO2 (see Dietzen et al., 2023) or a conservative estimate based on documented fertilizer application.
If direct measurement of anions is used, samples must be collected at or below the depth toof whichthe weathering is being monitoredNFZ (typically 3020 cm). Major anions should include NO3-, PO43-, Cl-, SO42- and any others that may be relevant to local land management practices and the feedstock being used. Measurement methods must comply with ISO 10304-1:2007. Unlike some soil based measurements in this Protocol, aqueous concentration of anions in porewaters will likely be dynamic and vary significantly over a Reporting Period. The Project Proponent must provide details of their sampling plan and describe how the chosen sampling frequency is appropriate for capturing any significant deviation in concentration at the project location.
The Project Proponent must describe in the PDD how site-based observations (e.g., precipitation, irrigation, other climatic variables, etc.) are used to determine the total volume of water infiltrated into the soil, and how discrete anion concentrations are combined with this data to determine the total amount of non-carbonic acid neutralization that occurred over the Reporting Period. Given a known volume of water infiltrated into the soil, [math: {CO}_{2}^{}e_{NonCarbonicNeut,\ RP}^{}] can be calculated as:
[math: {CO}_{2}^{}e_{NonCarbonicNeut,\ RP}^{}\ = \ \sum_{i}^{}c_{i}n_{i}]
(Equation 7)
Where:
Dietzen & Rosing (2023) describe a method for determining the proportion of weathering that occurs by reaction with carbonic acid based on carbonate speciation in soil porewater, as determined by measurements of soil pH and CO2 (Dietzen & Rosing 202326, equations 2-9). This formulation can be adapted to determine the proportion of weathering that occurs by reaction with non-carbonic acids using any two components of the carbonic acid system. Project Proponents may elect to account for non-carbonic acid neutralization using this method. Descriptions of the measurement and calculation methods must be provided in the PDD.
Where data is available, Project Proponents may choose to use fertilizer application rates as a proxy for non-carbonic acid weathering. Quantification of non-carbonic acid weathering from fertilizer records may come from:
Project Proponents must provide data on fertilizer application rates and calculations of the fraction of feedstock weathering resulting from non-carbonic acid weathering in the PDD. If non-carbonic acid neutralization is accounted for using fertilizer application rates, Project Proponents must provide evidence to justify the assumption that nitric acid is the only significant non-carbonic acid source. This includes measurements of total sulfur in the feedstock and in the soil.
[math: {CO}_{2}^{}e_{RiverineLoss,\ RP}^{}] includes all future losses that will occur in river systems downstream of in-field activities (the FFZ). In most cases, this will be a modeled result. Models used to estimate riverine losses must use historic river geochemical data to estimate relevant parameters. This may include publicly available datasets or scientific publications. The source of such data must be reported. Models must include explicit consideration of:
[math: {CO}_{2}^{}e_{MarineLoss,\ RP}^{}] includes all future losses that will occur after base cations are exported to the ocean. This must include explicit consideration of:
While this Protocol prescribes a minimum number of soils samples that must be collected for the quantification of removals, itIt may be appropriate in some cases to pool post-deployment samples for more resource-intensive analyses (e.g., analysis of trace metal abundance). Solid and liquid phase sample pooling is acceptable in crediting projects, with a maximum recommendation of 10 samples pooled per analysis. SamplesIt mustis strongly recommended that Project Proponents do not pool samples during baseline sampling events to ensure baseline heterogeneity in soil properties and geochemistry are fully appreciated. Note that liquid samples may be pooled inonly equalfor volumeselemental analysis and not for analysis of carbonic acid system parameters. All sample pooling plans must be approved by Isometric and described in the PDD.
As scientific consensus on EW continues to develop, redundant measurements are critical to understand carbon removal processes at the field scale. To this end, this Protocol requires that Project Proponents seeking Credits through Determination 1 conduct aqueous check measurements at lower spatial resolution to maximize confidence in calculated CDR. At a minimum, porewaters must be collected at the depth of lowest sampling (typically 30 cm) at a density of 1 porewater sampling device per 50 hectares (total project area). Samples must be collected in control and treatment plots in both the 2- and 3-plot models; aqueous check samples are recommended, but not required, in the deployment plot if using the 3-plot model. Deviation from depth and density requirements may be allowable in consultation with Isometric given site-specific considerations and must be justified in the PDD. Collected aqueous samples must be analyzed for at least two components of the carbonic acid system to calculate bicarbonate concentration; see guidance in Section 9.3.5.1.2. If the mean calculated CDR of aqueous measurements does not fall within the 95% confidence interval of CDR calculated by Equation 3, an audit must be conducted and Project Proponents will work with Isometric to determine a conservative solution.
Project Proponents pursuing Determinationsoil-based 1removal quantification must consider all terms listed in Equation 3, but alternative methods may be appropriate for rigorous quantification of CDR. For example, some Project Proponents may choose to monitor the loss of alkalinity in a project area by performing full sampleacid digests on soil samples withoutwith anylimited pre-processing (e.g. removal of carbonates, extraction of the soil exchangeable fraction). In this instance, weathering, cation sorption, carbonate formation and clay formation will all be integrated into a single measurement. Such deviations may be appropriate and will be considered on a project by project basis. In such cases, the Project Proponent must provide a detailed description of the methods and describe how the chosen analyses map onto the terms in DeterminationEquation 13 in the PDD.
Formerly part of Determination 2
InFor Determinationaqueous 2phase quantification, we make the simplifying assumption that all of the major soil column processes, including the release of base cations from weathering and soil losses, are accounted for in the aqueous geochemistry of water that has infiltrated to some depth. At this time, we are recommending athis depth coincide with the depth of 30the NFZ, typically 20 cm. Therefore, the total amount of carbon stored from an EW project can be determined from porewater measurements in the top 3020 cm of soil. Alternatives to 3020 cm may be justified for similar reasons described in the previous sectionsections. Well-defined catchment waters may be used in place of porewaters where the project area is contained entirely within such well-defined catchments. In the context of this Protocol, a catchment is considered well-defined if:
In instances where catchment waters are used, the Project Proponent must provide supporting documents detailing site-specific hydrogeology. [math: CO_2e_{Stored, \ RP}] can be calculated from the aqueous phase via the following equation:
[math: {CO}_{2}^{}e_{Stored,\ RP}^{} = {CO}_{2}^{}e_{Aqueous,\ RP}^{} \ – \ {CO}_{2}^{}e_{RiverineLoss,\ RP}^{} \ – \ {CO}_{2}^{}e_{MarineLoss,\ RP}^{}]
(Equation 8)
Where:
All terms have units of tonne CO2e.
Below is an overview of how each term is determined, with more details provided in Section 9.3.5. It is important to note that, although [math: {CO}_{2}^{}e_{BiomassLoss,\ RP}^{}] is not explicitly included in Determinationaqueous 2phase quantification, alkalinity may still be taken up by plants below the 30 cm observation window. Project Proponents using Determinationaqueous 2phase quantification for Credits must still consider and quantify
plant uptake if roots extend below the depth of porewater sampling.
[math: {CO}_{2}^{}e_{Aqueous,\ RP}^{}]: This is the integrated amount of CDR as determined from measurements of aqueous phase base cation abundance from water that has infiltrated to athe minimumdepth of 30the NFZ, typically 20 cm depth. There are two generally accepted approaches for determining aqueous phase alkalinity export: 1) direct measurements of cation and anion concentrations (e.g., via ICP-MS or ICP-OES) or 2) measurement of at least two carbonic acid system variables in solution. In both cases, Project Proponents must also produce a water budget for the project area encompassing the Reporting Period. Carbonic acid system measurements may include carbonate alkalinity titration to the CO2 equivalence point, pH, DIC and/or pCO2, followed by calculating the concentration of bicarbonate using the 2-for-6 method. Further guidance is given in Section 9.3.5.1.2.
[math: {CO}_{2}^{}e_{RiverineLoss,\ RP}^{}]: See DeterminationSolid 1Phase Quantification
[math: {CO}_{2}^{}e_{MarineLoss,\ RP}^{}]: See DeterminationSolid 1Phase Quantification
Project Proponents pursuing Determinationaqueous 2phase quantification must consider all terms listed in Equation 8, but alternative methods may be appropriate for rigorous quantification of CDR. For example, some Project Proponents may choose to directly observe cation and anion concentrations in collected waters. In this instance, weathering and multiple loss terms may be integrated into one result. Such deviations may be appropriate and will be considered on a project by project basis. In such cases, the Project Proponent must provide a detailed description of the methods and describe how the chosen analyses map onto the terms in DeterminationEquation 28 in the PDD.
Synthetic ion exchangers, more commonly referred to as ion exchange resins, have been employed in soil science for many years to constrain nutrient fluxes in the soil column (e.g. Lehman et al., 200126, Lang & Kaupenjohann, 200427, Johnson et al., 200528, Predotova et al., 201129, Grahmann et al., 201830). Typically, monitoring will consist of a vessel filled with a mixture of ion exchange resin beads and quartz sand that is buried in the soil column. Soil water then flows through the device and ions sorb to the resin beads, accumulating within the device. At the end of a sampling period, the accumulated ions are analyzed.
Ion exchange resins are a novel technique for EW measurements, with limited data on their use in EW deployments. For this reason, ion exchange resins may be used as a validation medium (List 2 in Section 7.4.1.1) under this Protocol. As more data becomes available, the use of ion exchange resins as a quantification medium will be revisited. Calculation of [math: CO_2e_{Stored, \ RP}] can be calculated as a validation check using ion exchange resins following Equation 8. Project Proponents using ion exchange resins for validation must provide detailed information on:
The resin(s) used, including documentation that demonstrates the resin(s) target the following:
Description of the installation procedure, particularly focusing on how the procedure mitigates against disturbance of pre-existing soil structure;
As ion exchange resins quantitatively remove dissolved ions from porewaters, the derived estimates of removals should utilize Equation 8, and should otherwise follow the recommendations and requirements pertaining to aqueous phase sampling wherever applicable.
Type: Counterfactual
[math: {CO}_{2}^{}e_{Counterfactual,\ RP}^{}] describes the CO2 that would have been removed from the atmosphere and durably stored in the baseline scenario, as a result of natural weathering or pre-existing land practices. This is calculated using the control plot, which must be subjectmaintained tounder business as usual farming practices. The control plot ensures that any removals associated with business as usual agricultural liming are not attributed to EW in agriculture projects. The control plot will serve as the baseline in modellingmodeling with respect to measured soil and porewater parameters. The approach used for this accounting, including the feedstock storage location, climatic conditions of the storage location, models used, and/or analyses conducted, must be provided and justified in the PDD.
In addition to counterfactual CO2 related to business as usual farming practices, in some instances it may be appropriate to consider weathering of feedstock that would have occurred without project intervention. For example, if the feedstock used constitutes a waste product that was not mined or quarried specifically for project activities and was stored in open-air conditions, some degree of surficalsurficial weathering could be expected over timescales relevant to a project lifetime. Project Proponents using these feedstocks must account for counterfactual weathering if the feedstock does not undergo additional processing prior to deployment. TheThis Isometric StandardProtocol defines the durability of aan enhanced weathering credit as 10001,000+ years; thus, this is the default assumption for the calculation timescale of counterfactual weathering if no additional information regarding the storage conditions and duration of the feedstock at the mine/quarry site can be provided. If additional information on the conditions and duration of feedstock storage at the feedstock supplier are available, Project Proponents may justify calculating the counterfactual across a time period relevant to the specific mine or quarry from which the feedstock is sourced in the PDD. For example, projects operating in conjunction with active mines may find it appropriate to use the time of mine closure and provide details of the closure plan in the PDD;. alternativelyAlternatively, if sufficient documentation exists suggesting that piles of waste materials generated by the feedstock will not be exposed to ambient environmental conditions for a period exceeding a set number of years, the counterfactual may be considered across that time span. It is important to note that studies have shown that the vast majority of weathering in tailings piles occurs in the surface layer that is exposed to the atmosphere, provided that there is no mechanical overturn (citations). For this reason, counterfactual weathering needs to be accounted for in the top meter of the tailings pile.
Where relevant, counterfactual weathering must be calculated by a combination of direct measurements and modeling of the expected weathering rate of feedstock under storage conditions relevant to the source site for either 10001,000 years or a time period justified in the PDD as described above. Models must be justified by empirical data from subsamples of the feedstock; guidelines for sampling procedures that adequately capture feedstock heterogeneity are described in the Rock and Mineral Feedstock Characterization Module. Models must take into account:
The measurements and model used to calculate counterfactual feedstock weathering must be provided to Isometric and the VVB. ProjectWhere Proponentscounterfactual mayweathering chooseis toconsidered, either[math: assumeCO_2e_{Counterfactual, \ RP}] is calculated as the totalsum of counterfactual weathering from business as ausual one-timefarming deductionpractice or to spread theand counterfactual deductionweathering acrossof a project lifetimefeedstock.
[math: {CO}_{2}^{}e_{Counterfactual,\ RP}^{}] from business as usual farming practice is determined using the same equations (Equations 7 and 8) as the previous section for [math: {CO}_{2}^{}e_{Stored,\ RP}^{}] in which all the encompassed terms are determined using a control plot of land as described in Section 9.3.1. Because the chemical composition of agricultural lime does not typically have sufficient concentrations of elements commonly used as immobile tracers, such as Ti, [math: CO_2e_{Stored}] in the control plot will be calculated as the change in concentration of Ca in the NFZ within a Reporting Period. This is a conservative assumption, as it assumes any change in Ca is attributable to weathering of agricultural lime.
For instances where the Project Proponent has discretion as to which methods can be used to determine a particular weathering or loss term, the methods used must be the same for both the area over which feedstock is applied and the control plot.
Type: Emissions
[math: {CO}_{2}^{}e_{Emissions,\ RP}^{}] is the total quantity of GHG emissions associated with a Reporting Period [math: RP]. This can be calculated as:
[math: {CO}_{2}^{}e_{Emissions,\ RP}^{}\ = \ {CO}_{2}^{}e_{Establishment,\ RP}^{}\ + \ {CO}_{2}^{}e_{Operations,\ RP}^{} + \ {CO}_{2}^{}e_{End-of-life,\ RP}^{}+ \ {CO}_{2}^{}e_{Leakage,\ RP}^{}]
(Equation 9)
Where:
The following sections set out specific quantification requirements for each variable. It is anticipated that most emissions associated with EW projects will occur during the Calculation of [math: {CO}_{2e}^{}e_{Establishment,\ RP}^{}] phase.
GHG emissions associated with [math: CO_2e_{Establishment,\ RP}] should include all historic emissions incurred as a result of project establishment, including but not limited to the SSRs set out in Table 1.
Project establishment emissions occur from the point of project inception through to after the spreading event has taken place. GHG emissions associated with project establishment may be allocated in one of the following ways, with the allocation method selected and justified by the Project Proponent in the PDD:
The anticipated lifetime of the project should be based on reasonable justification and should be included in the Project Design Document (PDD) to be assessed as part of project validation.
Allocation of [math: CO_2e_{Establishment,\ RP}] emissions to removals must be reviewed at each Crediting Period renewal and any necessary adjustments made. If the Project Proponent is not able to comply with the allocation schedule described in the PDD (e.g., due to changes in delivered volume or anticipated project lifetime), the Project Proponent should notify Isometric as early as possible in order to adjust the allocation schedule for future removals. If that is not possible, the Reversal process will be triggered in accordance with the Isometric Standard, to account for any remaining emissions.
GHG emissions associated with [math: CO_2e_{Operations\, RP}] should include all emissions associated with operational activities including but not limited to the SSRs set out in Table 1. For EW projects, the Reporting Period begins after the spreading event on agricultural land has occurred and ends once the weathering potential has been realisedrealized and MRV activitesactivities have ceased.
[math: CO_2e_{Operations,\ RP}] emissions occur over the Reporting Period for the deployment being credited and are applicable to the current deployment only. [math: CO_2e_{Operations,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreement with Isometric.
CO2e[math: CO_2e_{End-of-life,\ RP}] includes all emissions associated with activities that are anticipated to occur after the Reporting Period, but are directly or indirectly related to the Reporting Period. For example this could include ongoing sampling activities for MRV for the specific deployment (directly related) if applicable, or end-of-life emissions for project facilities (indirectly related to all deployments).
GHG emissions associated with [math: CO_2e_{End-of-Life,\ RP}] may occur from the end of the Reporting Period onwards, and typically through to completion of project site deconstruction and any other end-of-life activities.
GHG emissions associated with activities that are directly related to each deployment must be quantified as part of that Reporting Period. GHG emissions associated with activities that are indirectly related to all deployments may be allocated in the same ways as set out in [math: CO_2e_{Establishment,\ RP}].
Given the uncertain nature of [math: CO_2e_{End-of-Life,\ RP}] emissions, assumptions must be revisited at each Crediting Period and any neccesarynecessary adjustments made. Furthermore, if there are unexpected [math: CO_2e_{End-of-Life,\ RP}] emissions associated with a Reporting Period, or the project as a whole, that occur after the project has ended, then the Reversal process will be triggered to compensate for any emissions not accounted for.
[math: CO_2e_{Leakage,\ RP}] includes emissions associated with a project's impact on activities that fall outside of the system boundary of a project.
It includes increases in GHG emissions as a result of the project displacing emissions or causing a knock on effect that increases emissions elsewhere. This includes emissions associated with activity-shifting, market leakage and ecological leakage.
It is the Project Proponent's responsibility to identify potential sources of leakage emissions. For an EW project, feedstock replacement must be considered as part of the leakage assessment, as a minimum.
[math: CO_2e_{Leakage,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreementconsultation with Isometric.
This section of the Protocol outlines requirements for EW emissions accounting relating to energy use, transportation, and embodied emissions associated with a CDR project.
This section sets out specific requirements relating to quantification of energy use as part of the GHG Statement. Emissions associated with energy usage result from the consumption of electricity or fuel.
Examples of electricity usage may include, but are not limited to:
Examples of fuel consumption may include, but are not limited to:
The Energy Use Accounting Module v1.2 provides guidancerequirements on how energy-related emissions must be calculated in a CDR project so that they can be subtracted in the net CO2e removal calculation. It sets out the calculation approach to be followed for intensive facilities and non-intensive facilities and acceptable emissions factors.
Refer to Energy Use Accounting Module for the calculation guidelines.
This section sets out specific requirements relating to quantification of emissions related to transportation.
Emissions associated with transportation include transportation of products and equipment as part of a Reporting Period’s process. Examples may include, but are not limited to:
The Transportation Emissions Accounting Module v1.1 provides guidancerequirements on how transportation-related emissions must be calculated in a CDR project so that they can be subtracted in the net CO2e removal calculation. It sets out the calculation approach to be followed and acceptable emissions factors.
Refer to Transportation Emissions Accounting Module for the calculation guidelines.
This section sets out specific requirements relating to quantification of embodied emissions as part of the GHG Statement. Embodied emissions are those related to the life cycle impact of equipment and consumables.
Examples of project-specific materials and equipment that must be considered as part of the embodied emission calculation include but are not limited to:
The Embodied Emissions Accounting Module sets out the calculation approach to be followed including allocation of embodied emissions, life cycle stages to be considered, data sources and emission factors.
Refer to Embodied Emissions Accounting Module for the calculation guidelines.
This Protocol requires feedstock characterization and reporting in accordance with Isometric's Rock and Mineral Feedstock Characterization Module.
Refer to Rock and Mineral Feedstock Characterization Module for characterization guidelines.
Durability refers to the length of time for which CO2 is removed from the Earth's atmosphere.
The long-term storage reservoir for the alkalinity generated through EW is the ocean, where the removed CO2 is stored in the form of dissolved inorganic carbon (DIC). At typical sea surface conditions, about 90% of DIC is in the form of bicarbonate, while 9% is in the form of carbonate20. The durability of the ocean DIC reservoir can be described by its residence time, which is the average amount of time a substance stays in a particular reservoir. Residence time is definedcalculated by dividing the total inventory of a substance by the inflows or outflows, and assuming near-steady state conditions. It is scientifically well-established that the global ocean DIC residence time lies between 10,000 to 100,000 years6,2731. This is based on decades of research that estimates the global ocean DIC inventory to be between 37,000 and 39,000 GtC,2832, 2933, 3034 with a recent estimate being 37,200 ± 200 GtC3135. Additionally, the global riverine DIC inputs are well constrained to be between 0.3 to 0.4 GtC/yr4, 3236, 3337, 3236, which approximately balances the loss of DIC through carbonate precipitation and burial on the seafloor2731. Thus, the durability of EW as generated alkalinity is at least 10,000 years.
In the near-term when CDR is operating on small scales (i.e. [math: <]Gt), it is unlikely that CDR activities will result in meaningful changes to the global ocean DIC inventory or its input and output fluxes. Longer-term, elevated alkalinity in the ocean may lead to increased carbonate mineral production, which would remove alkalinity and decrease the residence time and durability of the global DIC reservoir. More research is needed to better understand these potential effects6.
Based on the present understanding, projects applicable to this Protocol are generally categorized as having a Very Low Risk Level of Reversal according to the Isometric Standard Risk Assessment Questionnaire. This is because reversals in the global ocean DIC reservoir will not be directly observable with measurements and attributable to a particular project, and EW as a pathway does not yet have a documented history of reversals. Instead, larger uncertainty discounts must be used to ensure conservatism. ARisk 2%of bufferreversal poolinformation mustis begiven setin asideAppendix as4: aRisk precautionof asReversal Questionnaire, with further information provided within the sciencerelevant evolves,storage andmodule thisstorage reversal risk and the stability of the ocean DIC reservoir will be reassessed when new scientific research and understanding arisesmodule.
Reversals will be accounted for by projects and the Isometric Registry as detailed in Section 5.6 of the Isometric Standard.
This section outlines an overview of the monitoring approach that Project Proponents must take in crediting projects. Several of the monitoring requirements described below include measurements that will be used in the quantification of rock spread and determination of removals (see Section 7.4).
A Project is a field or group of fields that are to be managed together for the purposes of deployments and crediting. A single Project Proponent may choose to have multiple Projects, each with an individual PDD, or group operations under a single Project. All deployments and sampling events across a Project must occur on similar timeframestime frames, which must be stated in the PDD.
There is no minimum or maximum Project area, however, projects must designate at least one control, treatment, and deployment plot (if using the 3-plot model) per 5002,000 hectares. Project areas exceeding 5002,000 hectares but less than 14,000 hectares will thus need to designate a minimum of 2 control, treatment and/or deployment plots; Projects exceeding 14,000 hectares but less than 16,500000 hectares will need to designateddesignate a minimum of 3 control, treatment and/or deployment plots; and so on. This lower limit is set primarily to avoid heterogeneity in factors that will influence weathering rate (e.g., precipitation).
Project Proponents with project areas distributed over large distances must maintain a set of plots for each region even if the area criteria listed above do not require it. This may include additional sets of plots per climatic and/or geo-political region, in consultation with Isometric. Difference in field and climatic characteristics (e.g., soil type, crop type, precipitation, temperature range, etc.) may also necessitate the maintenance of additional treatment and control sites. In all projects, the total number of control and treatment plots (where applicable) should each total at least 2.5% of the project area. Control, treatment and/or deployment plots will, in many cases, be contiguous, but this is not a requirement. This limit is set primarily to avoid heterogeneity in factors that will influence weathering rate (e.g., precipitation). In all projects, the total number of control and/or treatment plots (in a 3-plot model) should each total 5% of the project area. Furthermore, projects greater than 1,000 hectares must containmaintain a research plot. Research plot requirements are listed in Section 9.3.1.8. Projects may contain non-contiguous fields, managed by different farmers or landowners, so long as all plots are representative of each other, in accordance with Section 9.3.1.7.1.
Where applicable, analytical methods must be cross-referenced with an appropriate standardstandards (e.g., ISO, EN, BSI, ASTM, EPA) or standard operating procedureprocedures (SOP). Where a project utilizes a non-standardized methodology or SOP for the determination of a listed parameter, the Project Proponent is required to outline the relevant method within the PDD submitted to the Validation and Verification Bodies (VVB).
The Project Proponent has the choice between two monitoring frameworks in crediting projects: the 2-plot and the 3-plot approach.
Figure 2 Schematic of in-field monitoring approaches, illustrating the relative size of the control, treatment, and deployment plots in the 2- and 3-plot approaches, as well as CO2 drawdown from the atmosphere.
[Image: Section 1]
Table 2. Summary of Project Area.
| Area | 2-Plot | 3-Plot |
|---|---|---|
| Control | 2.5% of project area | 2.5% of project area |
| Treatment | 2.5% of project area | |
| Deployment | Not applicable |
The 2-plot approach for quantifying removals infrom EW in agriculture calls for the designation of the projectProject area into one of two categories:
The Treatment area is used to directly observe the CO2 removal resulting from EW in agriculture, while the control is used to directly observe counterfactual (or business as usual) CO2 removal. The 2-plot approach should be generally thought of as a flat, per-area sampling scheme.
The 3-plot approach allows for intensive, high -resolution data collection and monitoring of EW projects and itstheir counterfactualcounterfactuals at smaller scales, while monitoring the remainder of the project at lower resolution.
In this construction, the project area must be divided into three sections that will be designated as the control, treatment and deployment areas defined as follows:
Unless otherwise specified, the measurements collected in the control, treatment or deployment plots will be used to quantify removal terms contained within that particular area (i.e. deployment samples are used to quantify removals in the deployment plot). There may be some cases where measurements collected in the treatment area may be extrapolated to the deployment area (e.g., quantification of plant biomass uptake of base cations). Unless otherwise specified, the same number of samples must be taken from the control, treatment and deployment plots.
The purpose of thea control plot(s) is to quantify the removal that would have otherwise occurred without the application of rock or mineral feedstock. Most notably, this includes any CO2 removal effect of agricultural liming that would have occurred in the absence of project activities. The control area shouldmust represent a minimum of 2.5% of the total project area. The control area must be maintained using a continuation of historical agricultural practices, to represent what would have occurred otherwise in the absence of the CO2 removal project. This includes, for example, liming if EW is replacing current liming practices. If the Project Proponent is unable to maintain a control plot concurrent with the project deployment, the Project Proponent may opt to do the following:
In instances where the last 10 years of liming records cannot be obtained, the Project Proponent must work in consultation with Isometric to identify the most plausible counterfactual land management scenario. Examples of possible sources of information include signed affidavits from knowledgeable local individuals or aggregated county level records. The Project Proponent must detail the sources of this information in the PDD.
There may be some instances of the 2-plot approach where a 5% control area presents a significant financial and/or logistical challenge for the farmer maintaining the land. One such example may be a Project that includes a collection of small, non-contiguous farms, and each individual farmer is responsible for maintaining both plots separately. In such instances, the Project Proponent may reduce the control area to a minimum of 2% of the project area. The justification and circumstances surrounding this modification of the control area must be documented in the PDD.
The treatment (2-plot) encompasses the project area on which rock or mineral feedstock is applied. In most cases, this is 9597.5% of the project area. The treatment area will be subject to monitoring as prescribed by the sampling plan. Application of feedstock to the treatment area must be uniform unless otherwise stated (see Section 9.3.1.6.1: Variable Application Rates for further details).
The treatment (3-plot) must also represent a minimum of 2.5% of the total project area. If a Project Proponent opts to maintain control and treatment areas that are larger than 2.5%, it is recommended that these two areas maintain parity in both size and sampling density. The treatment area will be subject to intensive monitoring as prescribed by the sampling plan. Application of feedstock to the treatment area must be at the same feedstock volume per unit area as the deployment area.
The deployment area shall encompass the remaining project area that is not within the control or treatment plots. In most cases, this will represent 9095% of the project area.
In some cases, feedstock application rates may vary within a single deployment due to project-specific constraints, such as heterogeneity in soil characteristics or regional agricultural practice. These Projects may still be eligible for crediting under this Protocol.
As described in Section 9.3.4.4, this Protocol requires a soil-based determination of feedstock application to quantify the maximum Project CDR potential. Project Proponents utilizing variable application rates are required to submit application rate maps for the Project area. These maps can be generated from either recommended application rates supplied to the applicator (typically from farmer-supplied soil data) or directly from the applicator. This data must be used to design soil sampling plans such that the full range of application rate is captured. Projects seeking credits with variable application rates are required to designate control and treatment (if using a 3-plot model) areas that correlate with different application rates in the Project Area. For example, if application rate in a particular field varies from 1-4 tonnes/ha, the Project Proponent may subdivide this into two ranges of 1-2 tonnes/ha and 3-4 tonnes/ha, each with separate control plots. [math: CO_2e_{Stored,\ RP}] will be determined for areas with similar application rates, which will then be used to calculate a weighted average of [math: CO_2e_{Stored,\ RP}] for the full Project area.
The Project Proponent must designate one or more control areas that can be reasonably considered representative of the project area. Project Proponents should consider a range of climatic, soil, environmental, topographic, agronomic and hydrological properties contained within the project area when determining the representative plots. The following properties most relevant to weathering rate must be explicitly addressed in the PDD to demonstrate representativeness of the control: soil texture and composition, soil pH, local climate (temperature and precipitation), crop type and local hydrology. In irrigated fields, control plot designation must also consider spatial variation in irrigation rates. Project Proponents may use publicly available data sets for determining these site characteristics. All data and derived metrics used for designating field and control plots must be provided in the PDD. Where no data is available, the Project Proponent must undertake a soil survey to characterize relevant soil characteristics. Control plots based on the data provided in the PDD should capture both the central tendency and dynamic range of the listed control variables.
Some Project Proponents may choose to designate a contiguous area for the control area, however, this is not a requirement. The Project Proponent may designate two or more smaller areas that, in aggregate, represent 2.5% of the project area for either the control or treatment area. This might be done if field conditions do not readily allow for a single representative control and treatment areas.
In the 2-plot approach, the treatment area will consist of the remaining project area, which in most cases will be 9597.5% of the total project area.
Project Proponents must report the boundaries of the 2-plot designations, including project area maps, soil pH maps and soil texture maps with clearly demarcated boundaries and the GPS coordinates for the boundaries. It is recommended that the Project Proponent designates "buffer zones" near the edges of the control plots wherein samples will not be collected due to an elevated risk of feedstock migration. Geographical details on such designations must be reported.
The criteria for designating the treatment and control in the the 3-plot approach are the same as those described for the control in the 2-plot approach. Project Proponents must report the boundaries of the 3-plot designations as described in the 2-plot approach above.
Projects exceeding a total project area of 1,000 hectares are required to maintain research plots for the purpose of furthering scientific understanding of outstanding research question in EW projects. Research plots are required to include a control and experimental (treatment or deployment) plot, and may be located within the control, treatment, or deployment plots established for crediting. Project Proponents may choose the location and design of the research plot pursuant to specific scientific questions. It is recommended that research plots are designated such that maximum variability is captured. Research plot designations must be outlined and justified in the PDD for applicable projects.
Project Proponents meeting this criteria are required to trace the evolution of alkalinity down to at least 60 cm (but a recommended depth of 1 meter depth) using both soil and porewater measurements in the treatment and control areas. While only one analysis per plot is required per Reporting Period, the Project Proponent should use a similar depth partitioning and compositing framework applied in the rest of the project. Analyses of soil and fluid samples in the research plot must include all analyses required in Appendix 2.
Field management practices affect CO2 removal both directly and indirectly 3438,3539,3640. For example, irrigation can significantly impact both moisture and pH, therefore acting as a strong control on weathering rate3640. Some irrigation sources might contain significant amounts of alkalinity, influencing some quantification approaches. Furthermore, soil tilling can drive increased carbon flux in the upper soil column3438,3539,3741, which can complicate the calculation of stored carbon through gas-based field measurements. Thus, projects are required to provide detailed information on field management prior to feedstock deployment. Field management information includes:
Crop type
Productivity levels
IrrigationTillage sourcepractice
This includes bothIn the geographicevent locationthat ofa field is irrigated with a non-rainwater source and maintaining control plots that account for spatial variation in irrigation is operationally infeasible, Project Proponents must provide information on irrigation schedule and the irrigation source and characterization of fluid chemistry, including the following geochemical parameters:
pH
Project (Recommended)
If, at any point in the project duration, changes are implemented to any of the above field management strategies, the changes must be documented and reported. This includes a description of the change, the date the change was implemented and any required analyses associated with that field management strategy. For example, if the irrigation source changes, the fluid must be characterized according to the measurements listed above. Communication with agricultural partners should be established prior to deployment to facilitate data sharing. In extraordinary circumstances in which field management data cannot be provided, Project Proponents may still be eligible for Credits. In such cases, Project Proponents must justify why they are unable to provide this data in the PDD.
Climatic variables, such as temperature and precipitation, are strong controls of both feedstock reaction kinetics and the rate of alkalinity export 3640,3842. Thus, the project must provide climatic data from the project area. Climatic data includes:
The reported data must encompass the full time period for which crediting will take place. Acceptable data sources include sensors deployed directly in the project site or obtained from the geographically nearest weather station.
Inter-regional variability in rainfall can be significant even at the kilometer scale 3943, 4044. Because of the direct impact of rainfall on CO2 sequestration in agricultural EW, the project therefore must take microclimatic variation into account in collecting and reporting rainfall at the project site by deploying a rain gauge with data logging. This Protocol requiresrecommends that one rain gauge is installed per 5002,000 hectares. Project Proponents may propose alternative methods to account for rainfall at the project site if installation of a rain gauge is infeasible; for example, data from a weather station within 10 km2 distance from the project site.
This Protocol considers CO2 removal in terms of the alkalinity flux pastbeyond a soilthe depth after whichof the likelihood of permanent alkalinity loss (such as, via plant uptake or degassing) becomes considerably less likelyNFZ. Given the complexity of determining the depth atof whichthe CO2 can be reasonably considered capturedNFZ, as well as the operational difficulty of deep soil sampling, this Protocol sets a universal recommended sampling depth of 3020 cm (or tillage depth with additional buffer), with the expectation that this recommendation will be updated as more information becomes available. CO2 removal based on soil measurements will be calculated based on the alkalinity that reaches the determineddepth depthof the NFZ. However, we recognize the importance of accounting for temporal lags in alkalinity export from the soil column associated with cation sorption/desorption and formation/dissolution of secondary carbonates. To this end, Project Proponents are required to provide some constraints on alkalinity export from the chosen sampling depth (typically 30 cm) to the watershed (see Section 9.3.4.6.4)
ForTo aaccount for in-field heterogeneity, soil samplesamples toshould be representativeconsistent of a collection area, multiple soil cores mustor be taken to account for field heterogeneity. To minimize spatial noise, soil samples typically consist of 10-20 composited soil cores41,42,43subsamples. It is strongly recommended that soil samples be composed of 10-20 composited soil cores or subsamples randomly or arbitrarily distributed about a sample coordinate45, 46, 47. While this is a recommendation, Project Proponents are encouraged to consider increasing the number of composited cores per sample, especially in fields that have been characterized with a high level of spatial heterogeneity. The overall compositing procedure must be reported and justified in the PDD.
Sampling technique, including sampling design and methodology, type of sampling materials or machinery, must be stated in the PDD. andSignificant bechanges consistentto sampling procedures throughout the lifetime of the project lifespanmust be reported to Isometric.
This Protocol has multiple statistical considerations related to soil sampling. The first is a requirement for crediting, and the second is a guidance on determining the number of control, treatment and deployment samples needed for statistical significance.
AThe Project Proponent must demonstrate a statistically significant weathering signal in the quantification medium. If a project is utilizing soil-based quantification methods, a statistically significant decrease in the concentration of base cations in the weathering horizon (30 cm)NFZ must be observed in the treatment plot between the beginning and end of a Reporting Period. We recommend using a one-tailed t-test to demonstrate this statistical significance4448. Alternative statistical tests may be appropriate and may be justified based on characteristics of the data distribution (e.g., use Mann-Whitney U-test if data is not normally distributed). The Project Proponent may alternatively use a two-dimensional interpolation framework to estimate the spatially integrated weathering over the project area (with uncertainty explicitly quantified). In such cases, the interpolation scheme, uncertainty quantification routine and an appropriate test for statistical significance must be described in detail in the PDD.
A significance level of 0.05 must be used for all statistical tests (with the null hypothesis that there is no change in base cation concentration at the end of the reportingReporting periodPeriod compared to the earliest time point). Although there are a range of analyses that may be conducted to measure the abundance of base cations (relative to some immobile tracer), all statistical tests must be performed on base cation concentrations (e.g., mol/kg or g/kg) or base cation concentrations converted to units of equivalents of charge per kilogram of soil (e.g., eq/kg). The statistical test used, the input data and the result of this statistical test must be reported.
In cases where Project Proponents opt not to measure the relative concentrations of cations in soil immediately after deployment, the mean and uncertainty distribution of cation abundance at the start of the corresponding Reporting Period may not be known. For the purposes of demonstrating statistical significance, the Project Proponent may estimate the uncertainty of cation abundance immediately after spreading to be the same as the uncertainty observed at the end of the Reporting Period. This estimation can only be done for the first Reporting Period after feedstock is applied.
Projects using the 3-plot approach have one additional statistical requirement. This second requirement for crediting is that the Project Proponent must demonstrate the treatment area is sufficiently representative of the deployment area. This can be demonstrated through one of the following: 1) at the end of the Reporting Period, the base cation concentration is not statistically different between the deployment area and the treatment area (if not significantly different at the start of the Reporting Period), or 2) the change in base cation concentration over the entire Reporting Period is not statistically different between the deployment area and treatment area. For this statistical test, a two-tailed t-test is appropriate if data is approximately normally distributed,4448 but an alternative test may be used for the same reasons described in the above paragraph. A significance level of 0.05 must be used. The statistical test must be performed on base cation concentrationconcentrations (e.g., mol/kg or g/kg) or base cation concentrations converted to units of equivalents of charge per kilogram of soil (e.g., eq/kg). The statistical test used, the input data and the results of the statistical test must be reported. If the first statistical requirement is met, but it is found that the deployment is statistically different from the treatment area, an audit must be conducted to determine the likely source of the discrepancy. If no clear resolution is found, the deployment area may be credited at the lesser of the treatment and deployment plots (on a per area basis).
This Protocol prescribesrecommends, but does not prescribe, a minimum number of soil samples thatfor mustquantifying be collectedremovals. However, Credits will not be issued unless projects are able to achieve a statistically significant result within the Reporting Period. In some cases, this means that the Project Proponent may need to collect more than the minimumrecommended number of required samples. The number of samples needed to demonstrate statistical significance will depend on several factors, including the underlying weathering rate and the in-field heterogeneity. Project Proponents may find it useful to have some guidance on how many samples may be needed to demonstrate statistical significance given an estimate of the weathering rate and the in-field heterogeneity determined from post-deployment soil sampling. The following provides ansimplified estimateapproach ofto estimating the minimum number of samples needed to achieve statistical significance, assuming normally distributed data40,44, 4548, 4649, 50:
[math: N\ \geq \ \frac{2\sigma^{2}{Z_{\alpha}}^{2}}{{S_{\min}}^{2}}]
(Equation 10)
Where:
Using an estimate for weathering rates, the Project Proponent can derive the minimum number of samples needed to achieve statistical significance. We recommend that the Project Proponent uses an extremely conservative estimate of weathering rate or a safety factor above the calculated N when using this equation to determine the number of samples needed.
In rare cases, extreme operational difficulties may prevent Project Proponents from meeting the minimum sampling requirements shown in Table 3. Exceptions will be considered on a case-by-case basis. Examples of operational constraints that will be considered for claiming an exception to the sampling minimum include:
Project Proponents seeking an alternative minimum sampling plan must first seek approval from Isometric by providing a written explanation of the field conditions that require an alternative sampling minimum and a proposal for the alternative sampling plan. Such proposals must include justification of an alternative sampling minimum. This may take two different approaches:
Such alternative sampling plans must demonstrate the following criteria:
Projects will be subject to the same statistical requirements described elsewhere in this Protocol. Additionally, projects with approved alternative minimums will be subject to crediting at two standard deviations below the mean (or equivalent percentile for non-normal distributions). Since projects seeking alternative minimum sampling rates may not have adequate spatial coverage using soil or porewater measurements alone, proposals may include quantification frameworks that blend soil and porewater measurements.
Establishing baseline (i.e., before feedstock application) soil conditions is critical to both verifyverifying CO2 removal through EW activities and to facilitate monitoring ofmonitor potential environmental impacts. Project Proponents are therefore required to collect baseline soil samples prior to spreading rock or mineral feedstock. Baseline soil sampling should be conducted within the 2-plot or 3-plot framework described above. If pre-existing data on soil characteristics is unavailable, it may be appropriate to conduct additional baseline sampling prior to determining the boundaries of the control, treatment and deployment plots. Baseline samples are targeted to quantify heterogeneity in the soil characteristics most relevant to EW, including pH, soil texture, soil permeability, cation exchange capacity (CEC) and base saturation. Additionally, baseline sampling will allow the Project Proponent to determine the inherent heterogeneity of any tracer that may be used to determine rock or mineral feedstock addition. A full list of required analyses for baseline samples is given in Table 4. Baseline sampling must also quantify the abundances of all elements, isotopes and isotope ratios that will be used for quantification of feedstock weathering rate.
To minimize sampling bias, it is recommended that Project Proponents are required to collect soil samples in the weathering horizonNFZ (typically 3020 cm) at a minimumhigh spatial sampling density23 (e.g. 1 sample per hectare) in accordance with the Determinationquantification and validation approaches used for crediting, as outlined in Section 7.4.1. Sampling requirementsguidance for each determinationquantification approach are given in TableAppendix 3. InIf thea caseProject ofProponent theis utilizing a 3-plot approach, it is recommended that the total number of samples must be evenly divided between the three areas (i.e., one-third of the total number of samples collected in each plot). If equal number of samples between the 3 plots are not possible to collect in a certain deployment, Project Proponents must justify this in the PDD. While random sampling routines are generally preferred, the Project Proponent may use alternative sampling routines soas long as they are documented and justified in the PDD. After sampling, the soil cores may be divided into separate soil increment(s)increments or horizons and homogenized within each increment or horizon for analysis.
The Project Proponent is advised that the above baseline establishment sampling requirementsguidance representrepresents athe minimum numbersampling of samples that need to be collectedrecommendation. We encourage the Project Proponent to consider the impact of increasing the number of samples on the statistical significance threshold required for crediting.
This section deals with the determination of the total amount of feedstock-based alkalinity applied to a field during a deployment. This is a crucial part of the overall removal quantification sincebecause it sets the maximum potential CO2 removal. Given the importance of accurately determining the total amount of feedstock-based alkalinity added, this Protocol requires takingusing aaverage feedstock application rate data that is cross-validated against direct soil analysismeasurements.
While approachit is recommended that a sampling event occur immediately after application to directly measure feedstock application rate, followedthis byis confirmationnot a requirement so long as redundant determinations of the soils-based approach using the average application rate andare rockconducted alkalinityas contentdescribed below.
Determination of alkalinity added for a project is conducted by multiplying the average application rate (kg/m2) by the concentration of base cation alkalinity in the rock (eq/kg). Average application rate can be determined by either a) the average application rate of rock using records from the applicator or b) the total mass of rock added divided by the land area over which it was applied. This average application rate must then be multiplied by the moles of alkalinity per kilogram of rock, as outlined in the Rock and Mineral Feedstock Characterization Module.
The second method for determination of feedstock-based alkalinity added is meant to serve as an internal consistency check on the soils-based approach in the previous section. The total amount of feedstock-based alkalinity or base cations added to a site is determined by measuring the soil concentration of a particular immobile element, isotope or isotope ratio before and after feedstock application, and using the ratio between that analyte and feedstock alkalinity to determine the true feedstock application rate. While it is recommended that a sampling event occur directly after application, this is not a requirement as long as redundant determinations of application rate are conducted as described below.
Prior to application, the project area will be separated into two or three plots as described in Section 9.3.1. Baseline soil samples will be collected prior to the spreading of feedstock, with the same number of samples being collected in all control, treatment and deployment (if using 3-plot) plots. Soil samples shall be partitioned and analyzed as previously described. Following feedstock application, soil samples will be collected and analyzed in the same manner.
A mass balance approach is then used to determine the total mass of rock added in each offield thearea three(i.e., plots2-plot or 3-plot) separately:
[math: {\lbrack ITE\rbrack}_{PA,\ x}{mass}_{soil - PA,\ x} = \ {\lbrack ITE\rbrack}_{BL,\ x}{mass}_{soil - BL,\ x} + {\lbrack ITE\rbrack}_{FS}{mass}_{FS,\ x}\ ]
(Equation 11)
Where:
The Project Proponent may, in consultation with Isometric, provide an alternate form of the mass balance equation that is more appropriate for the specific tracers being used, which must be included in the PDD.
The mass of soil can be estimated using the product of soil density, sampledepth depthof the NFZ (typically 3020 cm) and the area of interest. Using the assumption that the total soil mass in the top 3020 cm is not significantly changed by rock application, Equation 11 can be rearranged to calculate the mass of rock added:
[math: {mass}_{FS,\ x} = \ \frac{(\lbrack{ITE\rbrack}_{PA,\ x} - \lbrack{ITE\rbrack}_{BL,\ x}){mass}_{soil,\ x}}{\lbrack{ITE\rbrack}_{FS,\ x}}]
(Equation 12)
[math: {mass}_{soil,\ x} = \rho_{x} \times d_{x} \times A_{x}]
(Equation 13)
Where:
The alkalinity application rate can then be calculated as follows:
[math: Alkalinity\ application\ rate = \frac{{(mass}_{feedstock,\ Treatment} + {mass}_{feedstock,\ Deployment})\ \times \lbrack Alk\rbrack_{feedstock}}{(A_{Treatment} + A_{Deployment})\ }]
(Equation 14)
The soil based alkalinity application rate must be reported in the initial Reporting Period (i.e. Reporting Period that includes the first measurements following deployment).
The second method for determination of feedstock-based alkalinity added is meant to serve as an internal consistency check on the soils-based approach in the previous section. This should be donedetermined by multiplying the average application rate (kg/m2see previous section) by the concentration of base cation alkalinity in the rock (eq/kg). Average application rate can be determined by either a) the average application rate of rock using records from an applicator or b) the total mass of rock added divided by the land area over which it was applied. This average application rate must then be multiplied by the moles of alkalinity per kilogram of rock, as outlined in the Rock and Mineral Feedstock Characterization Module.
The alkalinity application rate determined by this consistency check must be within three standard deviations (or 99.7% confidence interval) of the propagated uncertainty of the soils-based method in the previous sectionanalysis. If the alkalinity application rate determined by the consistency check is outside of this range, the Project Proponent may either conduct an audit of all project records to determine the likely source of the discrepancy or proceed using the lesser of the two alkalinity application rates.
To assess the theoretical maximum EW potential of a feedstock, an adjusted version of the Steinour equation is recommended 4751. This is described in further detail in the Rock and Mineral Feedstock Characterization Module.
Elemental abundance data should be produced according to methods prescribed in the Rock and Mineral Feedstock Characterization Module. The calculated CDR potential represents the upper limit of creditable removals for a single batch of feedstock as defined in the Rock and Mineral Feedstock Characterization Module. This Protocol does not currently allow for the crediting of removals from carbonate feedstocks. Therefore, any CaO or MgO that results from carbonate minerals must be omitted from the CDR potential calculation. Project Proponents are required to report the CDR potential of each batch of feedstock used pursuant to project activities in the PDD.
Randomized sampling is recommended to minimize potential sampling bias in quantification of soil characteristics 4852, 4953 . Alternative sampling frameworks may be appropriate. If a non-random sampling framework is used, the Project Proponent must describe the sampling approach and how it addresses in-field heterogeneity. The number of samples taken is dependent on the soil heterogeneity, as determined by baseline measurements, and the propagated analytical uncertainty of relevant measurements. It is recommended that Project Proponents seeking Credits through Determinationsoil-based 1 mustquantification analyze (on average) a minimum of 1 sample per hectare of project area (TableAppendix 3),; however, in cases of extreme heterogeneity, a higher average sampling density may be needed to achieve statistical significance. Guidance on determining the number of soil samples required for statistical significance is given in Section 9.3.4.2.
Soil sampling must be conducted at a cadence that is appropriate for the alkalinity fluxes being observed and the particular crops being grown. At a minimum, Project Proponents are required to conduct soil sampling shortlyprior beforeto rockfeedstock application (tobaseline verify the alkalinity application rate; see Section 9.3.4.4establishment) and annuallyonce aftera feedstockReporting applicationPeriod. It is recommended that Project Proponents maintain an annual minimum sampling cadence. It is further recommended that soil sampling is also conducted shortly after feedstock application to confirm the feedstock application rate (See Section 9.3.4.4 for further guidance). Sampling of water and biomass must be conducted at inveralsintervals that are appropriate for capturing those alkalinity fluxes. The cadence of sampling and justification must be described in the PDD. TheIt is recommended that the same number of soil samples must be taken from the control, treatment, and deployment plots if using 3-plot approach. An additional sampling period may be appropriate following any events that could significantly impact soil characteristics, such as fertilizer application, irrigation, or significant precipitation (e.g., major storm). This will be determined on a project- and event-specific basis. Sampling at a higher frequency than originally described in the PDD is always allowed.
In addition to regular sampling of the weathering horizonNFZ, annual sampling of deep soil (e.g., 60 cm to 1 m depth) is strongly recommended, as this will help Project Proponents to constrain the time scales of alkalinity transport through the soil column. A suite of recommended analyses for these samples is given in Table 4.
Table 3. Minimum Soil Sampling Density.
This Protocol requires robust characterization of all soil parameters related to quantification of CO2estored[math: CO_2e_{Stored}] in both baseline and post-application samples. Some measurements are required for all soil sampling events, some for baseline characterization, and some are recommended (see Table 4). This includes, but is not restricted to, the following measurements:
Details on requirements for soil characterization are given in Table 4.
The extent of feedstock weathering can be estimated in soil samples by monitoring the flux of base cations through the soil column to the depth of the NFZ and calculating dissolution using a mass balance-based approach. In this method, an immobile cationelement or tracer is measured against the flux of mobile base cations, commonly Ca2+ and Mg2+, and the extent of in-situ feedstock dissolution is calculated by mass balance:
[math: {\lbrack ALK\rbrack}_{add\ } = \ \lbrack ITE\rbrack_{add}\times\ \frac{{\lbrack ALK\rbrack}_{FS}\ - \ \lbrack{ALK\rbrack}_{BL}}{{\lbrack ITE\rbrack}_{FS} - {\lbrack ITE\rbrack}_{BL}}]
(Equation 1615)
Where:
[ALK]add -- the concentration of the added mobile cations (e.g., Ca2+, Mg2+)
[ITE]add -- the concentration of added immobile trace elementtracer
[ALK]FS -- the concentration of mobile cations in the feedstock
[ALK]BL -- the concentration of mobile cations in baseline soil samples
[ITE]FS -- the concentration of immobile trace elementtracer in the feedstock
[ITE]BL -- the concentration of immobile trace elementtracer in baseline soil samples
The mobile cation flux can then be determined by subtracting the cation concentration in post-application soil samples from the sum of the added cations and the baseline soil cation concentration:
[math: \Delta\lbrack ALK\rbrack\ = \ \lbrack{ALK\rbrack}_{add}\ + {\lbrack ALK\rbrack}_{BL}\ - \ \lbrack{ALK\rbrack}_{PAS}]
(Equation 1716)
Where:
Δ[ALK] -- the change in alkalinity (base cations) in the soil column between the beginning and end of the Reporting Period, in eq/kg
[ALK]add -- the concentration of the added mobile cations (e.g., Ca2+, Mg2+)
[ALK]BL -- the concentration of mobile cations in baseline soil samples
[ALK]PAS -- the concentration of the major mobile cations in post-application sample
The fraction of feedstock dissolutiondissolved is calculated as the cation flux divided by the added cations. Note that the set of equations given above (adapted from Reershemius et al. 2023) representrepresents one possible example of mass balance calculations and other calculation methods can be accepted5054. Additionally, Project Proponents shouldmust select an immobile tracer based on feedstock composition; this may include, for example, Ti, Zr, Th, Nb, Ta or rare earth elements (REEs). This approach requires that the concentration of the selected immobile element is sufficiently different between the soil (including additivesamendments such as fertilizers) and the chosen feedstock. Project Proponents should consider baseline variance of the chosen tracer in the project area and how this may impact the ability to resolve a weathering signal. Project Proponents are required to detail their mass balance calculation method and provide detailed justification for the selected immobile tracer in the PDD.
Project, Proponentsincluding areliterature required to detail their calculation method in the PDDreferences.
Cation concentrations in soil samples must be measured using a total digestion method coupled with either inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES). Project Proponents should consider the analytical precision required for detection of trace elements when selecting their measurement method. For example, sample analysis via ICP-OES may be appropriate for characterization of major elements, but lacks the analytical precision to accurately account for trace elements that may be used as immobile tracers. Project Proponents are required to describe their total digestion and measurement methods in the PDD. This should include consideration of cation sorption and secondary carbonate mineral formation where appropriate, such as extraction method for the soil exchangeable fraction (Section 9.4.6.3) or the method for removal of secondary carbonates before soil digestion. If Project Proponents are using a method that does not require explicitly accounting for SIC or cation sorption, this must be justified in the PDD. When reporting data from ICP-MS/OES, Project Proponents must include information on calibration standards, blanks, and certified reference materials (CRMs); requirements for data reports are described in the Rock and Mineral Feedstock Characterization Module.
Refer to Rock and Mineral Feedstock Characterization Module for characterization guidelines.
Project Proponents should cross-reference their measurement procedures with the following standards:
As applied feedstock weathers, a portion of the dissolved cation load will be transiently bound on soil exchange sites (the soil exchangeable fraction). Though uptake of dissolved cations by soil sites is temporary, it can affect short-term mass balance calculations for determining CO2 removed. Project Proponents are required to quantify the amount of base cations sorbed by soil for complete carbon accounting, which is calculated as the product of cation exchange capacity and base saturation. There are several potential methods that can be used to isolate the exchangeable fraction. These include (but are not limited to):
Project Proponents are required to outline their chosen extraction procedure for both CEC and base saturation, including post-extraction analysis, in the PDD, as well as justification of their choice. If Project Proponents are using an analytical method that does not require explicit accounting of sorbed cations, this must be justified in the PDD
Because of temporal lags in alkalinity export associated with cation sorption/desorption, Project Proponents are required to outline their approach to constraining the time between when weathering occurs and when bicarbonate is exported to the watershed. This may include:
Though these time estimates will not be used for Credit generation, Project Proponents are required to submit a report containing the estimated time series between mineral application and alkalinity export to the ocean as derived by the above methods.
Project Proponents aremust requiredconsider tothe accountimpact forof secondary mineral formation in soils as a result of EW activities,. includingSecondary carbonateminerals precipitationcan include both carbonates and secondarysilicate clay formationclays. Carbonate formation can be constrained as the difference in soil inorganic carbon (SIC) in the NFZ between baseline and post-application samples. This Protocol requires that SIC is measured via either calcimetry or thermo-gravimetric analysis, though alternative analytical methods, including ramped combustion coupled with infrared spectroscopy and powder x-ray diffraction, may be appropriate. The measurement used must be explained in the PDD. If Project Proponents are using an analytical method that does not require explicit accounting of SIC, this must be justified in the PDD.
Secondary clay formation shouldcan be investigated through x-ray diffraction analysis. Further mineralogical analysis, such as scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), can be used as an additional check. Secondary clay formation is difficult to quantify using widely accessible techniques at this time, and will not be counted towards CDR quantification.
Project Proponents should cross-check their methods with the following standards:
If alternative methods are used, relevant standards must be referenced in the PDD.
Some cations released during weathering reactions will be taken up by crops, thus creating a pool of reaction products outside of the soil. This Protocol requires that cations taken up by biomass are quantified. The requirements for biomass sampling are detailed in Section 7.4.1.
It is strongly recommended that Project Proponents are encouraged to monitor the flux of major GHGs (CO2, CH4, N2O) in control, treatment, and deployment (if using 3-plot) plots to monitor potential changes in short-term soil carbon cycling as a result of EW. This measurement can be accomplished with either gas flux chambers or eddy covariance towers and can be fully automated after installation. When using gas flux chambers, soil collars should be installed to a minimum depth of 5 cm. This Protocol recommends that flux chambers remain in the location of installation for a full growing season to appropriately monitor changes occurring during that time as a result of the project. Project Proponents are encouraged to install 1 gas analyzer per plot (control, treatment, and deployment) with a minimum of 5 gas flux chambers per analyzer. The gas flux chambers should be spaced to capture maximum field area and variability. When using eddy covariance towers, 1 tower per deployment is sufficient.
For both baseline sampling and the first year of project activities, gas samples should be collected continuously at equally spaced intervals. This can be automated using the appropriate software. Sampling rates after one year of deployment will be determined on a project basis.
Table 4. Summary of soil-based measurement requirements.
| Parameter | Rationale | Determination Method | Baseline and Deployment Requirements |
|---|---|---|---|
Calculation of CO2 removal | Total soil digestion coupled with ICP-MS or ICP-OES | Required for all sampling events | |
| Cation exchange capacity (CEC) | Assessment of soil quality Determination of exchangeable cations | Cation extraction coupled with analysis via ICP-MS/OES or AAS | Required for Required if used for calculation of CO2 removal |
| Base cation saturation | Assessment of soil quality Determination of exchangeable cations | Cation extraction coupled with analysis via ICP-MS/OES | Required for Required if used for calculation of CO2 removal |
| Soil inorganic carbon (SIC) | Determination of secondary carbonate formation | Calcimetry, Thermo-gravimetric analysis, Ramped combustion coupled with infrared gas analysis | Required for Required if used for calculation of CO2 removal |
| Soil moisture | Assessment of weathering potential | Oven drying | |
| Soil pH | Assessment of weathering potential Assessment of weathering progression | pH measurement in soil slurry | Required for all sampling events |
| Soil texture | Assessment of soil heterogeneity | Oven drying coupled with gravimetric sieving, Laser diffraction or x-ray scattering | Required for baseline samples Recommended for subsequent sampling events |
| Soil permeability | Assessment of soil heterogeneity | Water flow test | |
| Soil organic carbon (SOC) | Assessment of soil quality Calculation of CO2 removal Carbon cycle monitoring | Dry combustion, Walkley-Black method | Required |
| Total carbon content | Assessment of soil quality | Dry combustion | |
| Total sulfur content | Assessment of soil quality | Dry combustion | Required for baseline samples if using fertilizer records to account for non-carbonic acid weathering; Recommended for all sampling events |
| Soil bulk density | Assessment of soil quality | Drying and weighing | Required for baseline samples; Recommended for subsequent sampling events |
| Secondary clay formation | Determination of secondary mineral formation | X-ray diffraction | Recommended for all sampling events |
| Soil CO2 flux | Short-term carbon cycle monitoring | Gas flux chamber, Eddy covariance tower | Recommended for all sampling events |
| Carbon isotopes | Calculation of CO2 removal | Isotope ratio mass spectrometer (IRMS) | Optional for all sampling events |
Project Proponents may substitute required analyses with suitable alternatives in consultation with Isometric.
After feedstock application, pore watersporewaters must be sampled at a frequency that is appropriate for the local water budget and temporal evolution of dissolved ions. The porewater sampling plan must be described and justified in the PDD. The sampling plan should additionally consider events that significantly impact soil moisture, such as irrigation and heavy rainfall; this will be determined on a project- and event-specific basis.
It is recommended that Project Proponents pursuing Determinationa 2porewater-based are required toquantification install an average of 1 porewater collection device (e.g., lysimeter, rhizon) per 25 hectares of total project area to facilitate fluid sampling. Project Proponents pursuing porewater-based validation are recommended to install an average of 1 porewater collection device per 10 hectares in the observation plots (e.g., treatment and control), which is equivalent to 1 porewater collection device per 200 hectares of total project area. The type of porewater collection device and methodology must be stated in the PDD and be consistent throughout the project lifespan. Otherwise,unless Projectotherwise Proponentsapproved pursuingby Determination 1 must install porewater collection sampling devices at a frequency of 1 per 50 hectares for validation purposesIsometric. Porewater sampling devices should be installed atto the depth of deepestthe soil samplingNFZ for crediting (typically 3020 cm). Refer to Table 5 for more information on minimum liquid sampling density.
To facilitate calculation of alkalinity release, described below, it is strongly recommended that Project Proponents install a weighing lysimeter in addition to an in-situ drainage lysimeter, as weighing lysimeters can measure precipitation and evaporation rates of the weathering zone. Where this is infeasible, due to cost or accessibility, Project Proponents must demonstrate that evaporation can be sufficiently accounted for through a combination of measurements, climatic monitoring and models. This will be determined on a project basis. The porewater sampling plan must be described in full in the in PDD.
As part of the baseline establishment, Project Proponents are required to report local topographic and geologic data relevant to soil drainage patterns (e.g. water table depth, hydrologic maps, watershed boundaries, etc). Project Proponents may use publicly available data records to fulfill this requirement.
Table 5. Minimum Liquid Sampling Density.
Project Proponents utilizing fluid measurements to quantify removals must complete a full suite of fluid characterization measurements in both baseline and post-deployment samples, as outlined in Table 65.
Table 65. Summary of required and recommended measurements for fluid samples.
| Parameter | Rationale | Determination Method | Requirements |
|---|---|---|---|
| pH | Determination of weathering potential | pH meter | Required for |
| Temperature | Fluid characterization | Thermometer | Required if used for |
| Total alkalinity | Calculation of CO2 removal | Titration | Required if used for |
| Calculation of CO2 removal | Inductively coupled plasma mass spectrometry
(ICP-MS) OR Inductively coupled plasma optical emission spectroscopy (ICP-OES/ICP-AES) | Required if used for | |
| Non-carbonic acid acidity (anions) | Determination of non-carbonic acid neutralization | Ion chromatography | Required if used for |
| Dissolved inorganic carbon (DIC) | Calculation of CO2 removal Characterization of carbon pools | Acid titration | Required if used for |
| Electrical conductivity | Fluid characterization | Conductivity probe | Recommended for porewater samples |
| pCO2 | Calculation of CO2 removal | Gas equilibration coupled with gas chromatography, infrared detection | Recommended for porewater samples |
| Stable isotopes | Calculation of CO2 removal | Method will vary | Optional for porewater samples |
Project Proponents pursuing quantification of carbon removal via aqueous measurements may choose to monitor the carbonic acid system in porewater to calculate stored bicarbonate. To adequately constrain the carbonic acid equilibrium considerations in the weathering zone, Project Proponents selecting this option are required to measure at least two of the following parameters:
To reduce uncertainty in carbonic acid system calculations, it is highly recommended to measure all four of these parameters where possible. Bicarbonate (HCO3-) and carbonate (CO32-) can be subsequently calculated using the two-for-six method 5357, which is commonly accomplished using PHREEQC (typically used for freshwater) software (CO2SYS5458 is not recommended for calculations in the weathering zone). Project Proponents are required to submit data for all parameters of the carbonic acid system, both measured and calculated; where calculations were performed using methods other than PHREEQC, Project Proponents are required to submit the script or spreadsheet where the calculations were made.
Project Proponents pursuing quantification of carbon removal via aqueous measurements may choose to measure the concentration of base cations in porewater within the NFZ.
This Protocol recommends a full suite of elemental analyses in baseline pore water samples (see Rock and Mineral Feedstock Characterization Module). Porewater samplessample analyses taken post-application must include the elements utilized for removal quantification and those with potential health and environmental impact implications. This will be determined on a project basis. Porewater samples are required to be analyzed by either inductively coupled plasma mass spectrometry (ICP-MS; e.g., ISO 17294-1:2024) or inductively coupled plasma optical emission spectroscopy (ICP-OES; e.g., ISO 11885:2007) as the primary determination method. Project Proponents should take analytical precision and detection limits into account when determining their measurement method.
When reporting data from ICP-MS/OES, Project Proponents must include information on calibration standards, blanks, and CRMs; requirements for data reports are described in the Rock and Mineral Feedstock Characterization Module).
Project Proponents are required to account for any potential non-carbonic acid weathering that may occur in the upper soil column. If non-carbonic acid weathering is being determined from direct measurement of porewater cations, major anions should be measured in porewater samples by ion chromatography. Direct measurement of anions may not be necessary for projects that are calculating CO2e[math: CO_2e_{Stored}] based on measurements of the carbonic acid system. Project Proponents may electchoose to determineaccount the proportion of weathering that occurs byfor non-carbonic acid neutralizationweathering using thefertilizer calculationrecords methodif outlinedsufficient by Dietzen et al. 202326; thisinformation is available, as described in further detail in Section 7.4.1.12. All Project Proponents are required to explicitly outline how their approach accounts for non-carbonic acid weathering in the PDD.
The Project Proponent must demonstrate a statistically significant weathering signal in the medium that is being used to quantify removals for crediting. If a project is utilizing aqueous-phase quantification methods, the Project Proponent must demonstrate that the integrated export of base cations over the Reporting Period is statistically significantly higher in the treatment than in the control. We recommend using a one-tailed t-test to demonstrate this statistical significance48. Alternative statistical tests may be appropriate and may be justified based on characteristics of the data distribution (e.g., use Mann-Whitney U-test if data is not normally distributed).
A significance level of 0.05 must be used for all statistical tests (with the null hypothesis that there is no difference in base cation export over the Reporting Period). Although there are a range of analyses that may be conducted to measure the abundance of base cations (relative to some immobile tracer), all statistical tests must be performed on base cation concentrations converted to units of equivalents of charge exported over the Reporting Period. The statistical test used, the input data and the result of this statistical test must be reported.
As dissolved weathering products are exported from the upper soil columnNFZ, the generated alkalinity is transported through the watershedFFZ, with eventual durable CO2 storage in the oceans. The downstream transport of captured CO2 to the oceans may result in carbon losses through the following processes:
Carbon loss by re-equilibration of the carbonic acid system occurs following the dissolved inorganic carbon equilibrium reactions:
[math: {CO}_{2} + H_{2}O \leftrightarrow H_{2}{CO}_{3} \leftrightarrow H^{+} + {HCO}_{3}^{-} \leftrightarrow 2H^{+} + {CO}_{3}^{2 -}]
(Equation 1817)
Speciation of dissolved inorganic carbon (DIC) is pH-dependent, and mixing of two fluid parcels can result in outgassing from re-equilibration of these dissolved species5559.
Calcium carbonate forms by the following reaction:
[math: {Ca}^{2 +} + 2{HCO}_{3}^{-} \rightarrow {CaCO}_{3} + {CO}_{2} + H_{2}O]
(Equation 1918)
Calcium carbonate formation in rivers is quantified separately from calcium carbonate formation in soils because rivers represent an open system where dissolved CO2 can degas across the water surface. If calcium carbonate forms in rivers from dissolved weathering products, there is a maximum carbon loss potential of 50%, following the above reaction (Equation 1918). It is noted that, despite this inefficiency, carbonate minerals are a stable carbon sink on millennial timescales.
The fate of dissolved weathering products during river transport remains poorly constrained. To account for potential downstream losses, Project Proponents are required to model expected losses based on expected feedstock dissolution rate, watershed chemistry and river basin chemistry. These models should be based on publicly available historic watershed and river network data. Several recent publications have outlined modeling approaches that combine baseline river geochemical data, equilibrium modeling of water chemistry and scenarios of EW inputs5660, ,5761. For calcium carbonate precipitation, Harrington et al. (2023)5761 uses equilibrium modeling (PHREEQC), in combination with baseline river chemistry data available from UK rivers and estimated flux of weathering products, to assess changes in the calcite saturation index of rivers resulting from EW activities. Calcite saturation index is calculated as:
[math: {SI}_{c} = \log_{10}\left( \frac{\alpha{Ca}^{2 +} \times \ \alpha{CO}_{3}^{2 -}}{K_{sp(calcite)}} \right)]
(Equation 2019)
with
[math: K_{sp(calcite)} = \alpha_{sat}{Ca}^{2 +} \times \alpha_{sat}{CO}_{3}^{2 -}]
(Equation 2120)
Where:
[math: \alpha] = the measured solution activities of those ions
[math: \alpha_{sat}] = the ion activities at saturation
When SIc > 0, a river is considered supersaturated. Although supersaturation with respect to calcium carbonate does not necessarily result in calcium carbonate precipitation, typically, calcium carbonate precipitation is predicted at a saturation index > 15761.
Geochemical models of riverine losses must include the following parameters in both the full river network through which dissolved weathering products will be transported and the groundwater that drains from the deployment field to the river network:
Additionally, geochemical models must include expected cation and alkalinity fluxes to rivers from weathering activities to account for the maximum potential increase in SIc. Project Proponents are required to submit a detailed description of their modeling approach, including the model used, the river/watershed data used in model construction and the source of that data, in the PDD.
The eventual storage reservoir for durable carbon storage during EW is bicarbonate (HCO3-) and carbonate (CO32-) ions in the oceans. However, similar to carbon losses in rivers and watersheds, the following factors also lead to reduction of total CO2 removed when alkalinity generated from EW enters the ocean:
Calcium carbonate precipitation
Re-speciation of DIC
All of these processes can result in a reduction in total CO2 stored during an EW approach. This reduction should be accounted for upfront due to operating on timescales that are too long and spatial scales that are too large to directly monitor. For example, timescales on which CO2 removed during mineral spreading on croplands will reach the ocean are decadal 5761, 5862.
Abiotic calcium carbonate precipitation in the ocean is rare as spontaneous nucleation is strongly inhibited in seawater, and most carbonate production is thought to be biologically mediated6. Early stage studies have found no significant increase in biologically produced calcium carbonate at elevated alkalinity in the ocean 5963, 6064, but this is still an area where more research is needed. There is not yet scientific consensus on the impacts of biocalcification on the net CO2 removal from EW, and how calcifying plankton will respond to increased alkalinity from EW. However, because the alkalinity generated from EW will be greatly diluted by the time it reaches the ocean years later, impacts of calcium carbonate precipitation are expected to be minimal and can be ignored at this time.
The science of carbon speciation downstreamin ofthe weathering sitesFFZ is still evolving 6165, 6266, 6367, 6468. There are few studies that have specifically examined the amount of carbon lost during the processes operating in the ocean reservoir. Upper estimates from some peer-reviewed studies suggest that marine losses could amount to between 15-30% loss of carbon, depending on temperature, salinity and pCO26165, 6. Renforth and Henderson (2017)6 detail an uptake efficiency equation, quantifying the change in Total DIC as a function of change in Total Alkalinity in the ocean:
[math: \frac{\Delta C_T}{\Delta A_T} = \eta = (S \cdot 10^{-3.009} + 10^{-1.519}) \text{ln}(pCO_2)-(S \cdot 10^{-2.100}) - \\ (T \cdot pCO_2)(S \cdot 10^{-7.501} - 10^{-5.598}) - (T \cdot 10^{-2.337}) + 10^{-0.102}]
(Equation 2221)
Where:
pCO2 -- partial pressure of CO2 in equilibrium with the solution, in μatm
T -- temperature, in oC
S -- salinity, in %
𝛥CT -- change in Total DIC increase as a result of EW activity, in mol
𝛥AT -- change in Total Alkalinity increase as a result of EW activity, in mol
Project Proponents should identify which ocean basin into which their deployment sites are located drain into, based on river catchment flows, and use the oceanographic conditions from publicly available locationallylocation-specific time-series data, such as the NOAA climate indices list, OceanSODA-ETHZ, or equivalent, to the uptake efficiency (Equation 2221), to determine the appropriate deduction which should be used as the marine loss term in Equation 3. Equilibrium conditions can be assumed. These terms may also be calculated using software such as CO2SYS or PyCO2SYS 6569, 5458.
Quantification of marine losses will be updated in future versions of the Protocol in line with the best available science as more research in peer-reviewed literature is published.
In some cases, extreme, localized field heterogeneity may result in measurements or data that are missing, incomplete or out of line with expectations given the project design or previous measurements. Similarly, disruptions to the project area and ongoing monitoring (e.g., extreme weather events or equipment failure) may result in missing data, ouliersoutliers or unexplained results. For the purposes of this Protocol, outliers are defined as data that are more than three standard deviations from the mean (or equivalent percentiles for non-normal distributions). In such instances, the Project Proponent maymust seek clarification on how the data should be handled. When such instances occur, the details must be reported to the VVB and Isometric as quickly as possible after identification. In such situations, and on a case-by-case basis, Isometric will work to remedy the situation in consultation with the Project Proponent and VVB. Examples of possible remedies include omitting outliers that represent a highly improbable result or, replacing missing data with a conservative estimator of a group of samples collected from a nearby and likely representative area, or incorporating validation data into removal quantification.
All records associated with the characterization, design, deployment and monitoring should be kept for a minimum of 10 years after spreading of feedstocks on agricultural land, and submitted to proper authorities as required by local permitting regulations.
Projects that were started prior to the publicationcertification of this Protocol (V1.0, certified in April 2024) and spread feedstock within 6 months of publication (October 2024) may be eligible for crediting under this Protocol on a case-by-case basis. Project Proponents seeking Credits for pre-existing deployments must justify the approach taken in these Projects in the PDD, with special attention paid to:
Projects started prior to the publication of this Protocol are subject to the same statistical significance requirements referred to in Section 9.3.4.2.
Isometric would like to thank following contributors to this Protocol and relevant modules:
Isometric would like to thank following reviewers of this Protocol and relevant modules:
Refer to Appendix 1 of the Alkaline Feedstock Characterization Module.
This appendix details how the Project Proponent must monitor, document and report all metrics identified within this Protocol. Following this guidance will ensure the Project Proponent measures and confirms CO2e removedremoval and long-term storage compliance, and will enable quantification of the emissions removal resulting from the Project activity during the Project Crediting Period, prior to each Verification. This appendix includes some monitoring requirements that are required for all sampling events and some that are required for baseline samples only; this will be detailed in the notes section for each parameter.
This methodologyProtocol utilizes a comprehensive monitoring and documentation framework that captures the GHG impact in each stage of a Project. Monitoring and detailed accounting practices must be conducted throughout to ensure the continuous integrity of the CO2e removals and crediting.
The Project Proponent must develop and apply a monitoring plan according to ISO 14064-2 principles of transparency and accuracy that allows the quantification and proof of the GHG assessment.
| Parameter | Soil pH |
|---|---|
| Unit | N/A |
| Equation or Section(s) | Field Management, Designating Control and Treatment areas, Baseline Establishment, Soil Characterization |
| Description | Soil pH to be measured by slurry |
| Example Measurement Method/Data Source | Slurry pH probe. Refer to ISO 10390:2021. |
| Data Reporting Guidelines | Slurry probe must be calibrated regularly according to manufacturer instructions. Probe must be regularly tested against known standards. The results of standard measurements must be reported alongside data, including standard pH values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | Soil pH must be reported from soil samples from control, treatment, and deployment fields (in 3-plot approach) for all sampling events. |
| Parameter | Soil texture |
|---|---|
| Unit | % clay, % sand, % silt |
| Equation or Section(s) | Designating Control and Treatment areas, Baseline Establishment, Soil Characterization |
| Description | Soil texture is based on the grain size distribution of dried soil. |
| Example Measurement Method/Data Source | Soil texture can be obtained by oven drying and gravimetric sieving, as described in ISO 11277:2020 , or from publicly available soil data |
| Data Reporting Guidelines | Soil texture must be reported according to USDA guidelines of soil type. This must include percentages of sand, silt, and clay-sized particles as well as the classification of each soil sample based on those percentages. In the event that this requirement is satisfied by publicly available soil data, Project Proponents must report the agency from which this data was obtained, as well as the determination method and year of measurement. For measurements of soil texture, the results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | Soil texture must be reported from soil samples from control, treatment,
and deployment fields (in 3-plot approach) for |
| |
|
| Parameter | Soil organic carbon (SOC) |
|---|---|
| Unit | Mass fraction in soil (e.g., g/kg or equivalent) |
| Equation or Section(s) | Baseline Establishment, Soil Characterization |
| Description | Organic carbon content of soil samples |
| Example Measurement Method/Data Source | In accordance with the Walkley-Black method, dry combustion with a correction applied for carbonate formation, following ISO 10694:1995. Project Proponents may choose to pre-treat soil samples to remove the carbonate component prior to combustion. |
| Data Reporting Guidelines | The results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | SOC measurement is required for baseline sampling and must be reported from control, treatment, and deployment (if using 3-plot approach) plots. |
| Parameter | Cation exchange capacity (CEC) |
|---|---|
| Unit | mEq/100 g |
| Equation or Section(s) | Calculation of CO2estored, Equation 2, Equation 3, Baseline Establishment, Soil Characterization, Cation Exchange and Base Saturation |
| Description | Capacity of soil to retain cations (base cations + acid cations) |
| Example Measurement Method/Data Source | CEC is measured by cation extraction and subsequent measurement using
ICP-MS (ISO
17294-1: |
| Data Reporting Guidelines | The extraction method must be clearly described in the PDD. When reporting elemental data, Project Proponents must include data from calibration standards and CRMs as part of the data report. The results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | CEC must be reported from control, treatment, and deployment (if using 3-plot approach) plots for all sampling events if used to calculate [math: CO_2e_{stored}]. |
| Parameter | Base saturation |
|---|---|
| Unit | % |
| Equation or Section(s) | Calculation of CO2estored, Equation 3, Baseline Establishment, Soil Characterization, Cation Exchange and Base Saturation |
| Description | Percentage of soil active sites occupied by base cations (Ca2+, Mg2+, Na+, K+) in a soil sample; calculated as the sum of base cations divided by the CEC multiplied by 100. |
| Example Measurement Method/Data Source | Base saturation is measured by BaCl2 cation extraction (ISO
11260:2018) and subsequent
measurement using ICP-MS (ISO
17294-1: |
| Data Reporting Guidelines | The extraction method must be clearly described in the PDD. When reporting elemental data, Project Proponents must include data from calibration standards and CRMs as part of the data report. The results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | Base saturation must be reported from control, treatment, and deployment (in 3-plot approach)
fields. Required for baseline sampling. |
| |
| |
|
| Parameter | Total sulfur (soil) |
|---|---|
| Unit | ppm (mg/kg) |
| Equation or Section(s) | Soil Characterization |
| Description | Sulfur content of soil samples |
| Example Measurement Method/Data Source | Total sulfur must be measured by dry combustion of soil samples, following ISO 15178:2000. |
| Data Reporting Guidelines | Data reports must include standard data, including the standards used, number of standards analyzed, number of replicates, and percent error on the standard. |
| Additional Notes |
|
| |
| |
|
| |
| |
| |
| Parameter | Major and trace elements used for quantification |
|---|---|
| Unit | ppm (mg/kg) |
| Equation or Section(s) | Field Management, Calculation of CO2estored, Equation 3, Determination of Weathering |
| Description | Major and trace elements that may be released into the soil as a result
of project activities, with particular emphasis on the chosen immobile
trace element (e.g. Ti, Zr, REEs) and mobile base cations ( |
| Example Measurement Method/Data Source | This Protocol requires that major and trace elements be measured by a
total soil digest, following EPA Method 3050B, coupled with elemental analysis via ICP-MS (ISO 17294-1: |
| Data Reporting Guidelines | The digestion method must be clearly described in the PDD. When reporting elemental data, Project Proponents must include data from calibration standards and CRMs as part of the data report. The results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | Major and trace elements must be reported from control, treatment, and deployment (if using 3-plot approach) plots for all sampling events. |
| Parameter | Soil inorganic carbon (SIC, soil) |
|---|---|
| Unit | ppm (mg/kg) |
| Equation or Section(s) | Calculation of CO2estored, Equation 3, Equation 5, Equation 6, Secondary Mineral Formation |
| Description | Inorganic carbon content of soil samples |
| Example Measurement Method/Data Source | Inorganic carbon must be measured using either calcimetry (ISO 23400:2021) or thermogravimetric analysis (ASTM D8474-22). |
| Data Reporting Guidelines | Measurement methods must be described in the PDD.Data reports must include standard data, including the standards used, number of standards analyzed, number of replicates, and percent error on the standard. |
| Additional Notes | Total inorganic carbon must be reported from control, treatment, and
deployment (if using 3-plot approach) plots for all sampling events |
| |
| |
| |
| Parameter | Biomass uptake of cations |
|---|---|
| Unit | ppm (mg/kg) |
| Equation | Calculation of CO2estored, Equation 2, Equation 3, In-field Monitoring Approach |
| Description | Concentration of base cations ( |
| Example Measurement Method/Data Source | Plant material digestion coupled with elemental analysis via ICP-MS (ISO 17294-1: |
| Data Reporting Guidelines | The digestion method must be clearly described in the PDD. When reporting elemental data, Project Proponents must include data from calibration standards and CRMs as part of the data report. The results of standard measurements must be reported alongside data, including standard values, number of standards, number of replicates, and % error on standards. |
| Additional Notes | Biomass uptake is required for the control and treatment plots once per growing season at peak biomass. |
| Parameter | Porewater pH |
|---|---|
| Unit | N/A |
| Equation or Section(s) | Carbonic Acid System Measurements |
| Description | pH of porewater samples; one component of the carbonic acid system |
| Example Measurement Method/Data Source | pH is measured using a pH probe. |
| Data Reporting Guidelines | pH probe must be calibrated regularly according to manufacturer instructions. Probe must be regularly tested against known standards. The results of standard measurements must be reported alongside data, including standard pH values, number of standards, number of replicates, and % error on standards. 2-for-6 calculations to constrain the carbonic acid system must be reported, whether this was completed in CO2SYS (or similar), PHREEQC (or similar), or in an Excel sheet. When using calculation scripts/programs other than CO2SYS or PHREEQC, the script/program must be provided in the data report. The final data report must include all components of the carbonic acid system, both measured and calculated. |
| Additional Notes | Porewater pH must be reported from control, treatment, and deployment (if using 3-plot approach) plots. Required for all porewater analyses if used to calculate CO2estored. |
| Parameter | Porewater alkalinity |
|---|---|
| Unit | mg/L |
| Equation or Section(s) | Carbonic Acid System Measurements |
| Description | Total alkalinity of porewater samples; one component of the carbonic acid system |
| Example Measurement Method/Data Source | Alkalinity must be measured by titration, following ISO 9963-1:1994 . |
| Data Reporting Guidelines | Data reports must include information on the titration process, including acid type and concentration, sample mass, and sample dilution. Standards of known alkalinity must be regularly run using the same method as porewater samples. Data reports must include the standards used, number of standards run, and percent error on the standards. Project Proponents must describe their calculation methods for alkalinity in the PDD and provide a copy of the calculations in the report. Where a calculation script is used, a copy of the script must be provided.2-for-6 calculations to constrain the carbonic acid system must be reported, whether this was completed in CO2SYS (or similar), PHREEQC (or similar), or in an Excel sheet. When using calculation scripts/programs other than CO2SYS or PHREEQC, the script/program must be provided in the data report. The final data report must include all components of the carbonic acid system, both measured and calculated. |
| Additional Notes | Alkalinity must be reported from control, treatment, and deployment plots (in 3-plot approach). Required for all porewater analyses if used to calculate CO2estored. |
| Parameter | Dissolved inorganic carbon (DIC) |
|---|---|
| Unit | |
| Equation or Section(s) | Carbonic Acid System Measurements |
| Description | Total inorganic carbon dissolved in a porewater samples; one component of the carbonic acid system |
| Example Measurement Method/Data Source | DIC is measured by coulometric titration, sometimes coupled with infrared spectroscopy. The setup and measurement method must be described in detail in the PDD. |
| Data Reporting Guidelines | Standards of known DIC must be regularly run using the same method as porewater samples. Data reports must include the standards used, number of standards run, and percent error on the standards.2-for-6 calculations to constrain the carbonic acid system must be reported, whether this was completed in CO2SYS (or similar), PHREEQC (or similar), or in an Excel sheet. When using calculation scripts/programs other than CO2SYS or PHREEQC, the script/program must be provided in the data report. The final data report must include all components of the carbonic acid system, both measured and calculated. |
| Additional Notes | DIC must be reported from control, treatment, and deployment (if using 3-plot approach) plots for all porewater analyses if used to calculate CO2estored. |
| Parameter | pCO2 |
|---|---|
| Unit | μatm |
| Equation or Section(s) | Carbonic Acid System Measurements |
| Description | Partial pressure of CO2 in porewater; one component of the carbonic acid system |
| Example Measurement Method/Data Source | pCO2 in fluids is measured by equilibration of the fluid sample with a set headspace volume, followed by extraction of the headspace and analysis on a gas analyzer. pCO2 may be analyzed in-situ by sensors where possible. Sensor details must be reported in the PDD. |
| Data Reporting Guidelines | Where pCO2 is measured by equilibration, Project Proponents must report |
| Additional Notes | Where pCO2 is measured by equilibration, Project Proponents must report from the control, treatment, and deployment (if using 3-plot approach) plots. |
| Parameter | Dissolved major and trace elements used for quantification |
|---|---|
| Unit | |
| Equation or Section(s) | Calculation of CO2estored, Equation 3, Major and Trace Element Analysis |
| Description | Major and trace elements that may be released into porewater as a result of project activities. These elements must include cations that are most likely to be added to the system as a result of project activities (i.e. Ca, Mg, Na, K, P, Fe, Mn, Ni, Co, Cr). |
| Example Measurement Method/Data Source | This Protocol requires that major and trace elements be measured ICP-MS
(ISO |
| Data Reporting Guidelines | Sample preparation, including calibration standards and CRMs,
must be described in detail in the PDD. When reporting elemental data,
Project Proponents must include data from calibration standards and
CRMs as part of the data report. |
| Additional Notes | Major and trace elements must be reported from the control, treatment, and deployment (if using 3-plot approach) plots for all sampling events. Required for all porewater analyses if used to calculate CO2estored. |
| Parameter | Dissolved anions |
|---|---|
| Unit | |
| Equation or Section(s) | Calculation of CO2estored, Equation 3,Equation 7 |
| Description | Non-carbonic acid acidity (NO3-, PO43-, SO42-, Cl-) |
| Example Measurement Method/Data Source | Dissolved anions must be measured by ion chromatography. |
| Data Reporting Guidelines | Sample preparation, including standards, must be described in detail in the PDD. This must also include the eluent used during measurement. Standards of known anion concentrations must be regularly run using the same method as porewater samples. Data reports must include the standards used, number of standards run, and percent error on the standards. |
| Additional Notes | Dissolved anions must be reported from control, treatment, and deployment (if using 3-plot approach) plots. Required for all porewater analyses if necessary to calculate CO2estored. |
| Parameter | Temperature |
|---|---|
| Unit | ℃ |
| Equation or Section(s) | Climatic monitoring |
| Description | Temperature |
| Example Measurement Method/Data Source | Temperature is measured via thermometer. This Protocol requires that temperature is measured in-situ. |
| Data Reporting Guidelines | Project Proponents must report the thermometer used and locations/depths of their deployment. |
| Additional Notes | Temperature must be reported from control, treatment, and deployment (if using 3-plot approach) plots. Required for all porewater analyses if necessary to calculate CO2estored. |
| Area | 2-plot | 3-plot | ||||
|---|---|---|---|---|---|---|
| Control | 1/1 ha | 1/0. | ||||
| Treatment | 1/1 ha | 1/0. | ||||
| Deployment | N/A | 1/2. | ||||
| Control | 1/ | 1/ | 1 | |||
| Treatment | 1/ | 1/ | 1 | |||
| Deployment | N/A | N/A |
Note that all units in the above table are in soil samples per plot area. For example, a project utilizing a 3-plot model with soil-based quantification and a 1,000 hectare project area (25 ha control plot, 25 ha treatment plot, and 950 ha deployment plot) has a recommended minimum soil sampling 334 samples in the control, 334 samples in the treatment, 334 in the deployment.
| Aqueous | |||
|---|---|---|---|
| Area | 2-plot | 3-plot | |
| Quantification | Control | 1/25 ha | 1/1.875 ha |
| Treatment | 1/25 ha | 1/1.875 ha | |
| Deployment | N/A | 1/71.25 ha | |
| Validation | Control | 1/10 ha | 1/10 ha |
| Treatment | 1/10 ha | 1/10 ha | |
| Deployment | N/A | N/A |
Note that all units in the above table are in aqueous phase sampling devices per plot area. For example, a project utilizing a 3-plot model with porewater-based quantification and a 1,000 hectare project area (25 ha control plot, 25 ha treatment plot, and 950 ha deployment plot) has a recommended minimum aqueous phase density of 14 sampling devices in the control, 14 sampling devices in the treatment, and 14 sampling devices in the deployment.
This risk assessment identifies the pathway specific risk factors relevant to a carbon removal project. The relevant risk factors identified as part of a risk assessment are included in the monitoring plan requirements for the project, with details included in the Project Design Document. Project specific risk factors inform the required duration of monitoring along with the monitoring requirements set out in the Protocol and the requirements set out in the Monitoring Section of the Isometric Standard.
The risk score, as determined by the Risk of Reversal Questionnaire, will determine a project’s buffer pool contribution. Projects must re-assess their reversal risk at the renewal of each crediting period, or if monitoring identifies a reversal-related risk, or if an actual reversal event takes place. In any event, projects should reassess their reversal risk at a minimum every 5 years.
The Risk of Reversal Questionnaire questions that pertain to this protocol, drawn from the programme-level Risk of Reversal Questionnaire defined in Appendix B: Risk Reversal Questionnaire of the Isometric Standard, include the following:
| # in Isometric Standard Questionnaire | Question | If answered “Yes” | If answered “No” |
|---|---|---|---|
| 1 | Is a reversal directly observable with a physical or chemical measurement as opposed to a modeled result? | Proceed to questions 2-9 | Proceed to questions 8-9 |
| 8 | Is there 10+ years of monitoring and/or lab data demonstrating low project risk? | Minus up to 2 to Risk Score | |
| 9 | Does this pathway have a documented history of reversals? | Add 2 to Risk Score | |
| 10 | Is there one or more project-specific factors that merit a high risk level? | Add up to 2 to Risk Score |
Risk Score Categories
Project specific risk factors will depend on the form of carbon being stored (i.e., organic vs. inorganic), the method of storage (e.g., mineralization, encapsulation), the location of carbon storage (e.g., subsurface, ocean), and the proximity of that carbon to potential agents of reversal.
For projects with carbon storage as inorganic carbon, the presence of the following risk factors must be reflected in the risk score corresponding to question 10:
Walker, James CG, P. B. Hays, and James F. Kasting. (1981). A negative feedback mechanism for the long‐term stabilization of Earth's surface temperature. Journal of Geophysical Research 86(C10), 9776–9782. DOI: https://doi.org/10.1029/JC086iC10p09776↩
Ciais, Philippe, et al. (2014). Carbon and other biogeochemical cycles. Climate change 2013: the physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 465-570. ↩
Moon, S., Chamberlain, C. P., & Hilley, G. E. (2014). New estimates of silicate weathering rates and their uncertainties in global rivers. Geochimica et Cosmochimica Acta, 134, 257-274. Rendus de l’Académie Des Sciences), t. 323, 1007–1014. ↩
Gaillardet, J., Dupré, B., Louvat, P., & Allègre, C.J. (1999). Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers. Chemical Geology, 159, 3-30. ↩↩2
Dessert, C., Dupré, B., Gaillardet, J., François, L. M., & Allègre, C. J. (2003). Basalt weathering laws and the impact of basalt weathering on the global carbon cycle. Chemical Geology, 202(3), 257–273. https://doi.org/10.1016/j.chemgeo.2002.10.001↩
Renforth, P., & Henderson, G. (2017). Assessing ocean alkalinity for carbon sequestration. Reviews of Geophysics, 55(3), 636-674. https://doi.org/10.1002/2016RG000533↩↩2↩3↩4↩5↩6
Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926 ↩
Beerling, D. J., Leake, J. R., Long, S. P., Scholes, J. D., Ton, J., Nelson, P. N., Bird, M., Kantzas, E., Taylor, L. L., Sarkar, B., Kelland, M., DeLucia, E., Kantola, I., Müller, C., Rau, G., & Hansen, J. (2018). Farming with crops and rocks to address global climate, food and soil security. Nature plants, 4(3), 138–147. https://doi.org/10.1038/s41477-018-0108-y↩↩2
Kantola, I. B., Masters, M. D., Beerling, D. J., Long, S. P., & DeLucia, E. H. (2017). Potential of global croplands and bioenergy crops for climate change mitigation through deployment for enhanced weathering. Biology letters, 13(4), 20160714. https://doi.org/10.1098/rsbl.2016.0714↩↩2↩3
Haque, F., Santos, R. M., Dutta, A., Thimmanagari, M., & Chiang, Y. W. (2019). Co-Benefits of Wollastonite Weathering in Agriculture: CO2 Sequestration and Promoted Plant Growth. ACS Omega, 4(1), 1425–1433. https://doi.org/10.1021/acsomega.8b02477↩
Barak, P., Chen, Y., & Singer, A. (1983). Ground basalt and tuff as iron fertilizers for calcareous soils. Plant and Soil, 73(1), 155–158. https://doi.org/10.1007/BF02197765↩
Ma, J. F., Miyake, Y., & Takahashi, E. (2001). Chapter 2 Silicon as a beneficial element for crop plants. Silicon in Agriculture. Studies in Plant Science, Vol. 8. https://doi.org/10.1016/S0928-3420(01)80006-9↩
Chiaravalloti, I., Theunissen, N., Zhang, S., Wang, J., Sun, F., Ahmed, A. A., Pihlap, E., Reinhard, C. T., & Planavsky, N. J. (2023). Mitigation of soil nitrous oxide emissions during maize production with basalt amendments. Frontiers in Climate, 5. https://www.frontiersin.org/articles/10.3389/fclim.2023.1203043↩↩2↩3
Taylor, L. L., Quirk, J., Thorley, R. M. S., Kharecha, P. A., Hansen, J., Ridgwell, A., Lomas, M. R., Banwart, S. A., & Beerling, D. J. (2016). Enhanced weathering strategies for stabilizing climate and averting ocean acidification. Nature Climate Change, 6(4), 402–406. https://doi.org/10.1038/nclimate2882↩↩2
te Pas, E. E. E. M., Hagens, M., & Comans, R. N. J. (2023). Assessment of the enhanced weathering potential of different silicate minerals to improve soil quality and sequester CO2. Frontiers in Climate, 4. https://www.frontiersin.org/articles/10.3389/fclim.2022.954064↩↩2
Beerling, D. J., Epihov, D. Z., Kantola, I. B., Masters, M. D., Reershemius, T., Planavsky, N. J., Reinhard, C. T., Jordan, J. S., Thorne, S. J., Weber, J., Martin, M. V., Freckleton, R. P., Hartley, S. E., James, R. H., Pearce, C. R., DeLucia, E. H., & Banwart, S. A. (2023). Enhanced weathering in the U.S. Corn Belt delivers carbon removal with agronomic benefits (arXiv:2307.05343). arXiv. http://arxiv.org/abs/2307.05343↩
Ye, M., Song, Y., Long, J., Wang, R., Baerson, S. R., Pan, Z., Zhu-Salzman, K., Xie, J., Cai, K., Luo, S., & Zeng, R. (2013). Priming of jasmonate-mediated antiherbivore defense responses in rice by silicon. Proceedings of the National Academy of Sciences, 110(38), E3631–E3639. https://doi.org/10.1073/pnas.1305848110↩
Edwards, D. P., Lim, F., James, R. H., Pearce, C. R., Scholes, J., Freckleton, R. P., & Beerling, D. J. (2017). Climate change mitigation: Potential benefits and pitfalls of enhanced rock weathering in tropical agriculture. Biology Letters, 13(4), 20160715. https://doi.org/10.1098/rsbl.2016.0715↩↩2
Liang, Y., Nikolic, M., Bélanger, R., Gong, H., & Song, A. (2015). Silicon in Agriculture: From Theory to Practice. https://doi.org/10.1007/978-94-017-9978-2↩
Hartmann, J., West, A. J., Renforth, P., Köhler, P., De La Rocha, C. L., Wolf-Gladrow, D. A., Dürr, H. H., & Scheffran, J. (2013). Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification. Reviews of Geophysics, 51(2), 113–149. https://doi.org/10.1002/rog.20004↩↩2
ISO 14064-3: 2019, Section 5.1.7 ↩
Schneider, L., Schallert, B., & Kizzier, K. (2022). Methodology for assessing the quality of carbon credits. https://carboncreditquality.org/download/Methodology/CCQI%20Methodology%20-%20Version%203.0.pdf↩
Tautges, N. E., Chiartas, J. L., Gaudin, A. C. M., O’Geen, A. T., Herrera, I., & Scow, K. M. (2019). Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils. Global Change Biology, 25(11), 3753–3766. https://doi.org/10.1111/gcb.14762↩↩2
Almaraz, M., Bingham, N. L., Holzer, I. O., Geoghegan, E. K., Goertzen, H., Sohng, J., & Houlton, B. Z. (2022). Methods for determining the CO2 removal capacity of enhanced weathering in agronomic settings. Frontiers in Climate, 4, 970429. https://doi.org/10.3389/fclim.2022.970429↩
Wilson, M.J. (1999). The origin and formation of clay minerals in soils: past, present and future perspectives. Clay Minerals 34(1):7-25.doi:10.1180/000985599545957 ↩
DietzenLehmann, CJ., Kaiser, K., & RosingPeter, I. (2001). Exchange resin cores for the estimation of nutrient fluxes in highly permeable tropical soil. Journal of Plant Nutrition and Soil Science, 164(1), 57-64. ↩
Lang, F., & Kaupenjohann, M. T. (20232004). QuantificationTrace ofelement CO2release uptakefrom forest floor can be monitored by enhancedion weatheringexchange ofresin silicate minerals applied to acidic soilstubes. International Journal of GreenhousePlant GasNutrition Controland Soil Science, 125167(2), 103872177-183. https://doi↩
Johnson, D.org/10 W.1016/j, Verburg, P.ijggc S.2023 J.103872, & Arnone, J. A. (2005). Soil extraction, ion exchange resin, and ion exchange membrane measures of soil mineral nitrogen during incubation of a tallgrass prairie soil. Soil Science Society of America Journal, 69(1), 260-265. ↩
Predotova, M., Bischoff, W. A., & Buerkert, A. (2011). Mineral‐nitrogen and phosphorus leaching from vegetable gardens in Niamey, Niger. Journal of Plant Nutrition and Soil Science, 174(1), 47-55. ↩2
Grahmann, K., Verhulst, N., Palomino, L. M., Bischoff, W. A., Govaerts, B., & Buerkert, A. (2018). Ion exchange resin samplers to estimate nitrate leaching from a furrow irrigated wheat-maize cropping system under different tillage-straw systems. Soil and Tillage Research, 175, 91-100. ↩
Huang, W., Cai, W., Wang, Y., Lohrenz, S. E., & Murrell, M. C. (2015). The carbon dioxide system on the Mississippi River‐dominated continental shelf in the northern Gulf of Mexico: 1. Distribution and air‐sea CO2 flux. Journal of Geophysical Research. Oceans, 120(3), 1429–1445. https://doi.org/10.1002/2014JC010498↩↩2
Siegenthaler, U., & Sarmiento, J. L. (1993). Atmospheric carbon dioxide and the ocean. Nature, 365(6442), Article 6442. https://doi.org/10.1038/365119a0↩
Farquhar, G. D., Fasham, M. J. R., Goulden, M. L., Heimann, M., Jaramillo, V. J., & Kheshgi, H. S., et al. The carbon cycle and atmospheric carbon dioxide . https://www.ipcc.ch/site/assets/uploads/2018/02/TAR-03.pdf↩
Friedlingstein, P., Jones, M. W., O’Sullivan, M., Andrew, R. M., Bakker, D. C. E., Hauck, J., Le Quéré, C., Peters, G. P., Peters, W., Pongratz, J., Sitch, S., Canadell, J. G., Ciais, P., Jackson, R. B., Alin, S. R., Anthoni, P., Bates, N. R., Becker, M., Bellouin, N., … Zeng, J. (2022). Global Carbon Budget 2021. Earth System Science Data, 14(4), 1917–2005. https://doi.org/10.5194/essd-14-1917-2022↩
Keppler, L., Landschützer, P., Gruber, N., Lauvset, S. K., & Stemmler, I. (2020). Seasonal Carbon Dynamics in the Near-Global Ocean. Global Biogeochemical Cycles, 34(12), e2020GB006571. https://doi.org/10.1029/2020GB006571↩
Li, M., Peng, C., Wang, M., Xue, W., Zhang, K., Wang, K., Shi, G., & Zhu, Q. (2017). The carbon flux of global rivers: A re-evaluation of amount and spatial patterns. Ecological Indicators, 80, 40–51. ↩↩2
Ludwig, W., Amiotte Suchet, P., & Probst, J.-L. (1996). River discharges of carbon to the world’s oceans: Determining local inputs of alkalinity and of dissolved and particulate organic carbon. Sciences de La Terre et Des Planètes (Comptes https://doi.org/10.1016/j.ecolind.2017.04.049↩
Sainju, U. M., Jabro, J. D., & Stevens, W. B. (2008). Soil carbon dioxide emission and carbon content as affected by irrigation, tillage, cropping system, and nitrogen fertilization. Journal of Environmental Quality, 37(1), 98–106. https://doi.org/10.2134/jeq2006.0392↩↩2
Dencső, M., Horel, Á., Bogunovic, I., & Tóth, E. (2021). Effects of Environmental Drivers and Agricultural Management on Soil CO2 and N2O Emissions. Agronomy, 11(1), Article 1. https://doi.org/10.3390/agronomy11010054↩↩2
Cipolla, G., Calabrese, S., Porporato, A., & Noto, L. V. (2022). Effects of precipitation seasonality, irrigation, vegetation cycle and soil type on enhanced weathering – modeling of cropland case studies across four sites. Biogeosciences, 19(16), 3877–3896. https://doi.org/10.5194/bg-19-3877-2022↩↩2↩3
Haddaway, N. R., Hedlund, K., Jackson, L. E., Kätterer, T., Lugato, E., Thomsen, I. K., Jørgensen, H. B., & Isberg, P.-E. (2017). How does tillage intensity affect soil organic carbon? A systematic review. Environmental Evidence, 6(1), 30. https://doi.org/10.1186/s13750-017-0108-9↩
Larkin, C. S., Andrews, M. G., Pearce, C. R., Yeong, K. L., Beerling, D. J., Bellamy, J., Benedick, S., Freckleton, R. P., Goring-Harford, H., Sadekar, S., & James, R. H. (2022). Quantification of CO2 removal in a large-scale enhanced weathering field trial on an oil palm plantation in Sabah, Malaysia. Frontiers in Climate, 4, 959229. https://doi.org/10.3389/fclim.2022.959229↩
Sivakumar, M. V. K., & Hatfield, J. L. (1990). Spatial variability of rainfall at an experimental station in Niger, West Africa. Theoretical and Applied Climatology, 42(1), 33–39. https://doi.org/10.1007/BF00865524↩
Fiener, P., & Auerswald, K. (2009). Spatial variability of rainfall on a sub‐kilometre scale. Earth Surface Processes and Landforms, 34, 848–859. https://doi.org/10.1002/esp.1779↩↩2
Ferguson, R. B., Hergert, G. W., Shapiro, C. A., & Wortmann, C. S. (2007). Guidelines for Soil Sampling. University of Nebraska-Lincoln--Extension, Institute of Agriculture and Natural Resources.https://extensionpubs.unl.edu/publication/g1740/pdf/view/g1740-2007.pdf↩
Ackerson, J. (2018). Soil Sampling Guidelines. Purdue University Extension. https://www.extension.purdue.edu/extmedia/AY/AY-368-w.pdf↩
Austin, R., Gatiboni, L., Havlin, J. (2020). Soil Sampling Strategies for Site-Specific Field Management. North Carolina State Extensionhttps://content.ces.ncsu.edu/soil-sampling-strategies-for-site-specific-field-management#section_heading_7377↩
https://ocw.mit.edu/courses/18-05-introduction-to-probability-and-statistics-spring-2014/resources/mit18_05s14_reading18/↩↩2↩3↩4
https://ocw.mit.edu/courses/18-05-introduction-to-probability-and-statistics-spring-2014/resources/mit18_05s14_reading22/↩
Singh, A., & Masuku, M. (2014). Sampling Techniques and Determination of Sample Size in Applied Statistics Research: An Overview. International Journal of Commerce and Management, 2, 1–22. ↩
Gunning, P.J., Hills, C.D., Carey, P.J. (2010). Accelerated carbonation treatment of industrial wastes. Waste Management. Volume 30, Issue 6, p. 1081-1090. https://doi.org/10.1016/j.wasman.2010.01.005↩
Stolbovoy, V., Montanarella, L., Filippi, N., Selvaradjou, S.-K., Panagos, P., & Gallego Pinilla, F. J. (2005). Soil Sampling Protocol to Certify the Changes of Organic Carbon Stock in Mineral Soils of European Union. ↩
Chaney, D. (2017). Common Research Designs for Farmers. SARE. https://www.sare.org/publications/how-to-conduct-research-on-your-farm-or-ranch/basics-of-experimental-design/common-research-designs-for-farmers/↩
Reershemius, T., Kelland, M. E., Jordan, J. S., Davis, I. R., D’Ascanio, R., Kalderon-Asael, B., Asael, D., Suhrhoff, T. J., Epihov, D. Z., Beerling, D. J., Reinhard, C. T., & Planavsky, N. J. (2023). Initial validation of a soil-based mass-balance approach for empirical monitoring of enhanced rock weathering rates. https://doi.org/10.48550/ARXIV.2302.05004↩
Tipper, E. T., Stevenson, E. I., Alcock, V., et al. (2021). Global silicate weathering flux overestimated because of sediment–water cation exchange. Proceedings of the National Academy of Sciences, 118(1), e2016430118. ↩
Kemp, S. J., Lewis, A. L., & Rushton, J. C. (2022). Detection and quantification of low levels of carbonate mineral species using thermogravimetric-mass spectrometry to validate CO2 drawdown via enhanced rock weathering. Applied Geochemistry, 146, 105465. https://doi.org/10.1016/j.apgeochem.2022.105465↩
CO2 in Seawater: Equilibrium, Kinetics, Isotopes, Volume 65—1st Edition. (2001) https://shop.elsevier.com/books/co2-in-seawater-equilibrium-kinetics-isotopes/zeebe/978-0-444-50946-8↩
Humphreys, M.P., Lewis, E.R., Sharp, J.D., Pierrot, D. (2022). PyCO2SYS v1.8: marine carbonate system calculations in Python. Geoscientific Model Development 15, 15–43. https://doi.org/10.5194/gmd-15-15-2022↩↩2
Zhang, S., & Planavsky, N. J. (2019). Revisiting groundwater carbon fluxes to the ocean with implications for the carbon cycle. Geology, 48(1), 67–71. https://doi.org/10.1130/G46408.1↩
Zhang, S., Planavsky, N. J., Katchinoff, J., Raymond, P. A., Kanzaki, Y., Reershemius, T., & Reinhard, C. T. (2022). River chemistry constraints on the carbon capture potential of surficial enhanced rock weathering. Limnology and Oceanography, 67(S2), S148–S157. https://doi.org/10.1002/lno.12244↩
Harrington, K. J., Hilton, R. G., & Henderson, G. M. (2023). Implications of the Riverine Response to Enhanced Weathering for CO2 removal in the UK. Applied Geochemistry, 152, 105643. https://doi.org/10.1016/j.apgeochem.2023.105643↩↩2↩3↩4
Raymond, P. A., Hartmann, J., Lauerwald, R., Sobek, S., McDonald, C., Hoover, M., Butman, D., Striegl, R., Mayorga, E., Humborg, C., Kortelainen, P., Dürr, H., Meybeck, M., Ciais, P., & Guth, P. (2013). Global carbon dioxide emissions from inland waters. Nature, 503(7476), 355–359. https://doi.org/10.1038/nature12760↩
Subhas, A. V., Dong, S., Naviaux, J. D., Rollins, N. E., Ziveri, P., Gray, W., Rae, J. W. B., Liu, X., Byrne, R. H., Chen, S., Moore, C., Martell-Bonet, L., Steiner, Z., Antler, G., Hu, H., Lunstrum, A., Hou, Y., Kemnitz, N., Stutsman, J., … Adkins, J. F. (2022). Shallow Calcium Carbonate Cycling in the North Pacific Ocean. Global Biogeochemical Cycles, 36(5), e2022GB007388. https://doi.org/10.1029/2022GB007388↩
Gately, J. A., Kim, S. M., Jin, B., Brzezinski, M. A., & Iglesias-Rodriguez, M. D. (n.d.). Coccolithophores and diatoms resilient to ocean alkalinity enhancement: A glimpse of hope? Science Advances, 9(24), eadg6066. https://doi.org/10.1126/sciadv.adg6066↩
Fuhr, M., Geilert, S., Schmidt, M., Liebetrau, V., Vogt, C., Ledwig, B., & Wallmann, K. (2022). Kinetics of Olivine Weathering in Seawater: An Experimental Study. Frontiers in Climate, 4. https://www.frontiersin.org/articles/10.3389/fclim.2022.831587↩↩2
Griffioen, J. (2017). Enhanced weathering of olivine in seawater: The efficiency as revealed by thermodynamic scenario analysis. Science of The Total Environment, 575, 536–544. https://doi.org/10.1016/j.scitotenv.2016.09.008↩
Montserrat, F., Renforth, P., Hartmann, J., Leermakers, M., Knops, P., & Meysman, F. J. R. (2017). Olivine Dissolution in Seawater: Implications for CO2 Sequestration through Enhanced Weathering in Coastal Environments. Environmental Science & Technology, 51(7), 3960–3972. https://doi.org/10.1021/acs.est.6b05942↩
Beerling, D. J., Kantzas, E. P., Lomas, M. R., Wade, P., Eufrasio, R. M., Renforth, P., Sarkar, B., Andrews, M. G., James, R. H., Pearce, C. R., Mercure, J.-F., Pollitt, H., Holden, P. B., Edwards, N. R., Khanna, M., Koh, L., Quegan, S., Pidgeon, N. F., Janssens, I. A., … Banwart, S. A. (2020). Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature, 583(7815), 242–248. https://doi.org/10.1038/s41586-020-2448-9↩
Pierrot, D., Lewis, E., Wallace, D.W.R., 2006. MS Excel Program Developed for CO2 System Calculations, in: Tech. Rep. Presented at the Carbon Dioxide Inf. Anal. Cent., Oak Ridge Natl. Lab., US DOE, Oak Ridge, Tennessee. ↩