Orals: Mon, 28 Apr | Room 2.95
Mati Carbon uses basalt-based Enhanced Rock Weathering (ERW) to supplement the income of smallholder farmers while promoting climate resilience. In facilitating future participation in carbon markets for smallholder farmers, Mati provides opportunities for agronomic benefits for individual partnered farmers while paving the way towards economically viable, gigaton scale CDR in regions throughout the Global South.
Currently, Mati operates at scale (100,000 tons of basalt deployable per annum) at centralized locations within Chhattisgarh and Madhya Pradesh. These states of India have a large number of smallholder rice paddy farmers. The regional Indian farming practice involves flooding and vigorous wet tilling of rice paddies, creating homogenized soil ideal for basalt integration. Rice paddies have two primary growing seasons: Rabi (winter, dry season) and Kharif (summer, monsoonal season).
For each deployment, Mati monitors the crop yield for all enrolled farmers. Many of our partnered farmers do not deploy basalt on all of their fields, which allows for comparison of the crop yield in deployed versus control plots. Along with biomass measurements and crop density estimations, we conduct detailed farmer surveys to monitor the agricultural practices of each enrolled farmer and the performance of their crops after ERW deployment. Additionally, rice yield estimates from farmers are reported to the Indian government.
In 2024 Mati deployed 22,402 metric tons of basalt with 344 farmers at the Madhya Pradesh site and 49,880 metric tons with 711 farmers in Chhattisgarh. In 2023 Mati deployed 7,898 metric tons of basalt with 293 farmers in Chhattisgarh. Here, we compare mean yield changes for rice production across the Kharif (summer monsoonal season). Combining internally collected survey data and rice yield figures reported to the government, we conduct a meta-analysis of the rice yield data from our partnered farmers. We report significant mean production increases for rice yield. Throughout the Chhattisgarh Kharif in 2023 the mean increase for rice productivity (kg/ac) was 14.39% (n=162). In the 2024 Kharif, the mean increase in rice yield at Chhattisgarh was 27.79% (n=44). In the 2024 Kharif season at Madhya Pradesh, the mean measured yield increase was 18.79% (n=18). We estimate that partnered smallholder farmers in India benefitted by an integrated income increase of over one million dollars through our 2024 ERW deployments. This income increase is due to both incremental increases in productivity and reduced input costs.
How to cite: Jordan, J., Das, A., Bernstein-Schalet, J., Agarwal, S., Planavsky, N., and Beerling, D.: Enhanced rock weathering for improved farmer welfare in the Global South: An at-scale case study for rice agriculture in India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18512, https://doi.org/10.5194/egusphere-egu25-18512, 2025.
Enhanced weathering (EW) of silicate rocks such as basalt is a promising carbon dioxide removal (CDR) technology1. Various potential agronomic co-benefits are suggested for silicate rock powders in the tropics2 but there are few studies conducted under commercial field deployment conditions.
In this study we report the effects of basalt rock powder applied to sugarcane grown on an oxisol in Brazil, SP. The experiment was directly embedded within the commercial fields of the farm and set up in August 2023 as a randomized block design with four treatments (0, 10, 50, 100t/ha; surface applied) and four replicates. Agronomic management was kept identical to the operations of the farm. Soil samples were analyzed for various soil health parameters including cation exchange capacity, pH, organic matter, and macro- and micronutrients. Different biometric parameters and nutrient uptake were measured in the sugarcane. Additionally, CO2 emissions were monitored and soil water was analyzed for pH, EC, DIC, and nutrients. Detailed multi-parameter results from one year of post-application monitoring of the experiment are presented, drawing comparison to positive yield results across the commercial scale deployment.
1 David J. Beerling et al., Nature 583, no. 7815 (July 2020): 242–48
2 Philipp Swoboda, Thomas F. Döring, and Martin Hamer, Science of The Total Environment 807 (February 10, 2022): 150976
How to cite: Swoboda, P., Larkin, C. S., Rodrigues, M. M., Kang, J., Santoro, M., Clarkson, M. O., and Chiapini, M.: Agronomic co-benefits of enhanced rock weathering (ERW) with basalt applied to sugarcane grown on acidic soil in Brazil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12326, https://doi.org/10.5194/egusphere-egu25-12326, 2025.
Warm and humid climatic conditions in tropical regions can optimise the efficiency of enhanced rock weathering (ERW) as a carbon dioxide removal pathway. However, the potential of agronomic co-benefits (e.g., yield, nutrition, soil health) that might result from treating crops with silicate rock powder are less constrained, particularly in the context of smallholder farming that is ubiquitous throughout tropical regions like Sub-Saharan Africa. In March 2024, Flux coordinated with the United Nations Convention to Combat Desertification (UNCCD) on a pilot study to assess the impact of ERW on crop performance at 56 smallholder farms in Kisumu County, Kenya using standard farming practices. Selected plots consisted of maize and baseline measurements indicate that soils were slightly acidic (6.4 on average). Each plot was divided into control and treatment sections, with the latter amended with mafic feedstock (0-4 mm) at a rate of 20 tonnes ha-1. Differences in soil parameters (e.g., pH, nitrogen, organic carbon, phosphorus) and crop metrics (e.g., grain yield, cob length, kernels per cob) between control and treatment plots were assessed. Yield data was collected at harvest, ca. 14 weeks after rock powder application and sowing, Our findings demonstrate significant agronomic benefits, with an average yield increase of 71.17% ± 15.5% and an aggregate yield increase of 47.47% ± 5.73% in maize yield on treatment plots compared with the control plots. While confirmation via post-application soil sampling is still outstanding, the observed yield increase is potentially attributable to the liming effect of the rock powder and to the contained mineral nutrients, in particular phosphorus. The monetary value of the yield increase is substantial, exceeding on average $326 USD ha-1. Collectively, our preliminary data from the UNCCD trial appear to demonstrate rapid impacts from ERW on agronomic performance in Kenya, translating to robust economic benefits at the community level.
How to cite: Haque, F., Clementi, V. J., Möller, B., Bastianini, L., Odhiambo, C., Sagina, S., and Davies, S.: The agronomic impact of enhanced weathering deployments in Sub-Saharan Africa: Insights from a smallholder field trial in Kisumu County, Kenya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7491, https://doi.org/10.5194/egusphere-egu25-7491, 2025.
Despite increasing scientific interest in Enhanced Rock Weathering (ERW) and a rapid growth of commercial operations in this field, reliable and affordable methods for Monitoring, Reporting and Verification (MRV) remain a critical challenge for upscaling. Soil-based MRV methods provide an upper-bound estimate for Carbon Dioxide Removal (CDR) established through the quantification of feedstock weathering rates. However, robust CDR calculations require accounting for various cation loss pathways, such as plant uptake and soil sorption, necessitating extensive and costly measurements, each with the potential to introduce uncertainty into the CDR estimate. Porewater-based MRV methods, which aim to quantify the export of CDR-relevant aqueous-phase weathering products, also present challenges. These methods typically rely on specialized water extraction instruments that can be expensive to procure, install and maintain, and may not function reliably under low soil moisture conditions. Furthermore, solute flux calculations derived from discrete porewater samples are dependent on accurate water balance estimates, and often involve interpolating data gaps, potentially introducing uncertainty. As commercial ventures continue to explore ERW, developing reliable and scalable MRV methodologies is essential for ensuring the credibility and widespread adoption of this CDR strategy.
We propose the use of ion-exchange resin devices, known as Self-Integrating Accumulators (SIAs), as a potential improvement for MRV of ERW. Originally developed to determine nutrient leaching in soils1, SIAs offer the potential for cost-effective and robust time-integrated measurements of subsoil cation and anion fluxes relevant to CDR quantification. The performance of SIAs adapted for this purpose was evaluated in a series of mesocosm-scale weathering experiments, primarily designed to assess the adsorption efficiency and recovery rates of major ions used for MRV.
Preliminary experiments, utilizing basaltic feedstock (applied at an equivalent rate of 200 t/ha) and agricultural soil sourced from western Germany, demonstrated high (>90%) major ion adsorption efficiencies by SIA devices, despite the induction of strong weathering fluxes. The second phase of this research employed a lower application rate (100 t/ha) to more closely simulate feasible operational deployments. We present here initial findings from this series of experiments, aiming to demonstrate the applicability of SIAs for large-scale ERW deployments, which we believe could significantly improve the accuracy, cost-effectiveness, and efficiency of MRV.
References
1Bischoff, Wolf-Anno. 2007. “Development and Applications of the Self-Integrating Accumulators: A Method to Quantify the Leaching Losses of Environmentally Relevant Substances.” PhD Thesis, Berlin, Germany: Technische Universität Berlin. https://depositonce.tu-berlin.de/items/64e16848-244b-4b50-920c-8d835efda918.
How to cite: Michaelis, T., Faria, G., Bisping, C., Bischoff, W.-A., Schwarz, A., and Oehm, T.: Evaluating the performance of ion-exchange resin devices as an MRV tool in mesocosm-scale weathering experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19360, https://doi.org/10.5194/egusphere-egu25-19360, 2025.
How to cite: Michel, P.: In-Situ Alkalinity Efflux Monitoring: A Novel Sensor for ERW Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12475, https://doi.org/10.5194/egusphere-egu25-12475, 2025.
Enhanced rock weathering (ERW) – the introduction of finely crushed alkaline minerals into agricultural soils – could in principle remove billions of tonnes of carbon dioxide annually at the global scale. However, questions remain over processes leading to the formation and persistence of soil inorganic carbon via ERW, especially amidst the complexity of conditions across Earth’s cropland soil. Here we present a new model, a COUpled Soil Inorganic-organic carbon model for eNhanced wEathering (COUSINE), which mechanistically simulates carbon dioxide removal (CDR) via ERW across diverse climate and soil conditions. COUSINE considers the dynamics of 20 chemical species in the soil system that are driven by soil CO2 dynamics, parent material, soil cation exchange, secondary mineral formation, strong and weak acid weathering, plant and microbial activity, and leaching of elements from the soil system. Principles of mass and charge conservation are maintained across all reactions. We applied the model to various climate and soil conditions – from fertile temperate Alfisols to highly and extremely weathering subtropical Ultisols and tropical Oxisols – to examine the key controls over weathering rates and CDR rates. Our simulations reveal three key limitations in regulating the timing and potential of carbon sequestration under ERW. First, organic acids and clay colloids in fertile soils retain cations in environments with low base saturation and relatively high CEC, creating strong cation sinks, thus delaying increased pore water alkalinity in response to alkaline mineral additions. This lag can be substantial, lasting for over 80 years in Alfisols with high CEC capacity to less than 20 years in Oxisols, which lack cation exchanging organic matter and minerals. Second, competition between carbonic acid and other sources of protons can limit the efficacy of CDR. This is apparent in net nitrogen acidity from nitrogen fertilizer applications, which results in strong acid weathering. Third, climate conditions related to excess moisture and soil temperature control reaction kinetics, which affects the rate at which cations are released into solution and can thus participate in bicarbonate formation. COUSINE informs matrix simulations across soil properties, climates, and application rates, thereby elucidating optimal conditions for maximizing soil carbon sequestration via ERW, providing a new tool for CDR verification
How to cite: Tao, F. and Houlton, B.: Key limitations in enhanced weathering to remove carbon dioxide across agricultural soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5064, https://doi.org/10.5194/egusphere-egu25-5064, 2025.
Enhanced weathering (EW) of silicate minerals on agricultural fields is a promising natural carbon dioxide removal (CDR) method that has potential co-benefits for soil health and crop safety. However, the scalability of EW is suffering from labor-intense requirements of soil pore water extraction for monitoring, reporting and verification (MRV) of carbon credits. Furthermore, in-field extraction of soil pore water for MRV can be challenging as existing methods, such as rhizon samplers or ceramic suction cups, may lose vacuum or be ineffective at low moisture levels, leading to insufficient volumes of sample obtained for chemical analysis. Critically, the volume of soil from which pore water is drawn using these conventional methods will differ depending on soil moisture content and pore connectivity, making it difficult to determine the precise volume of soil sampled and consequently adding further uncertainty to CDR estimates. Here, a novel method for extracting weathering products from soil for determination of EW and CDR (termed “SAT-C”) is presented. SAT-C attempts to alleviate some of the limitations of traditional soil pore water extraction by obtaining weathering products from a known soil volume. In the SAT-C approach, a soil sample is saturated using de-ionized water and subsequently centrifuged in order to separate the sample into aqueous and solid phases, both of which are later analyzed for weathering products. In this study, SAT-C was applied to cores extracted from the upper 5-10 cm of the soil profile at two different EW deployment sites, where conventional rhizon and ceramic suction cups are also installed at 10 and 5-10 cm depths, respectively. Base cation and anion concentrations for all three methods were in the same order of magnitude. Estimated bicarbonate from the charge balance of major cations and anions correlated well with measured alkalinity across the two different soil types. In addition to comparable pore water chemistry, the SAT-C method offers the quantitative estimation of water filled porosity (which is needed for a direct measure for the field wide pore water reservoir of CDR at that point in time) that conventional methods lack. Furthermore, the method is not inhibited by low levels of field moisture during the crop growing season.
How to cite: Skov, K., Radkova, A., Arn Teh, Y., Kelland, M., Reershimius, T., Manning, D., Frew, A., Gazzagon, G., Bierowiec, T., Chen, E., Harrity, S., Agace, K., Tostevin, R., Turner, W., and Liu, X.: Novel extraction method designed to estimate the topsoil pore water reservoir of carbon dioxide removal through enhanced weathering of silicate minerals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15975, https://doi.org/10.5194/egusphere-egu25-15975, 2025.
To achieve the 2°C climate goal various carbon dioxide removal (CDR) technologies are being developed. Biochar obtained from biomass pyrolysis contains persistent carbonaceous compounds and offers benefits when applied to soil, including enhanced soil fertility, and improved water retention. Additionally, the application of natural rocks for enhanced rock weathering (ERW) in agricultural soil is gaining attention for its potential to sequester CO2, while increasing soil pH and providing essential nutrients. Given the promising potential of both biochar and ERW as CDR technologies, their combined application could offer synergistic effects, making it crucial to understand their interaction. However, research on their co-application of biochar and rock powder as well as co-pyrolysis of biomass with rock powder (yielding rock enhanced biochar) remains limited.
This study quantified alkalinity and ion releaseOxisol soil columns after addition of wood and straw biochar, rock-enhanced biochar or co-application of biochar and rock powder. In total 9 treatments were incubated for 27 weeks under elevated CO2 conditions with 10 leachate sampling events. First results show high initial fluxes of total alkalinity and dissolved inorganic carbon as well as dissolved organic carbon and nutrients, which decrease over time. Notably, pCO2 has minimal impact on the pyrogenic carbon, while it doubles the total alkalinity flux from ERW. While biochar alone creates a larger carbon sink, co-applying rock powder enhances mineral fertilization and increases the weight of biochar pellets. Soil amendments with biochar further prevent a water logging of the clayey Oxisol, enabling rock weathering and alkalinity fluxes to continue.
How to cite: Vorrath, M.-E., Amann, T., Linke, T., Meyer zu Drewer, J., Hagemann, N., Aldrich, C., Börker, J., Seedtke, M., Hagens, M., Eschenbach, A., and Hartmann, J.: Synergistic effects of co-application and co-pyrolysis of biochar and enhanced weathering materials for CO2 removal in an Oxisol, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12717, https://doi.org/10.5194/egusphere-egu25-12717, 2025.
Enhanced rock weathering (ERW) is a method of carbon dioxide removal (CDR) that relies on the weathering of mineral feedstock in the soil upper layers. Current ERW models, estimating CDR potential from the local site, primarily examine mineral dissolution and ion exchange processes via abiotic pathways within soil columns at mesocosm/plot scale. These models often simplify or overlook the interactions between soil, plants, and carbon dynamics under rock applications. Here, we present a novel integrated modelling approach, coupling an ERW model, SMEW (Bertagni et al., 2024), with the mechanistic ecohydrological model T&C-BG (Fatichi et al., 2019). Our coupled model T&C-SMEW can explicitly represent the hydrological, vegetation dynamics and soil biogeochemical cycling of carbon, nitrogen, phosphorus, potassium and micro-nutrients (Ca2+, Mg2+, Si) with the aid of T&C-BG, while incorporating mineral dissolution dynamics of SMEW. Additionally, T&C-SMEW accounts for key mechanisms such as a) biological weathering related to the release of H+ following realistic plant cation uptakes under varying environmental conditions, and b) strong acid weathering due to N fertiliser applications on crop field. Validated against both mesocosm and field experiments, T&C-SMEW can capture soil mineral exchanges and ecosystem carbon dynamics, demonstrating its reliability for representing ERW application in practical scenarios. By utilising T&C-SMEW, the direct CDR potential (e.g., mineral weathering) of ERW, its co-benefits (e.g., enhanced plant productivity), and associated environmental risks (e.g., phosphorus leaching) can be comprehensively assessed.
How to cite: Zhang, Z., Jones, G., Calabrese, S., Bertagni, M., Waring, B. G., and Paschalis, A.: Modelling the impacts of enhanced rock weathering on soil-plant-carbon cycle: develop and benchmark on mesocosm and field experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10422, https://doi.org/10.5194/egusphere-egu25-10422, 2025.
Ocean alkalinity enhancement (OAE) is a potential ocean-based carbon dioxide (CO2) removal approach that involves the addition of alkaline substances to the marine environment to increase seawater buffering capacity and allow it to absorb more atmospheric CO2. Increasing seawater alkalinity can trigger mineral precipitation, consuming the added alkalinity and decreasing OAE efficiency. To explore mineral formation as a result of alkalinity addition, we present results from laboratory experiments conducted by adding alkalinity as an aqueous solution of either NaOH or Na2CO3 to unfiltered seawater collected from Vineyard Sound near Woods Hole, Massachusetts, USA. The seawater used in the experiments is characterized by an average total alkalinity (TA) value of 2158 µmol/kg and an average dissolved inorganic carbon (DIC) value of 2043 µmol/kg. The amount of alkalinity added was 2000, 5000, and 10000 µmol/kg. The carbonate chemistry was monitored through time by measuring TA and DIC, which were used to calculate the saturation state Ω with respect to a number of minerals including carbonates and brucite. The amount and mineralogy of the precipitate through time were determined in order to monitor the mineralogical changes of the precipitated phases. Results show that mineral precipitation took place in all experiments where alkalinity was enhanced except in the experiment where 2000 µmol/kg was added as Na2CO3. In all experiments where precipitation was visually observed, TA and DIC decreased with time. In the NaOH experiments, TA decreases while DIC remained constant for a period of time, followed by the decrease of both TA and DIC in a 2:1 ratio. In the Na2CO3 experiments, TA and DIC decreased in a 2:1 ratio throughout the duration of the experiment. These trends are interpreted to reflect the initial precipitation of brucite followed by carbonate minerals in the NaOH experiments and the precipitation of only carbonate minerals in the Na2CO3 experiments. Raman Spectroscopy data confirmed the formation of brucite, aragonite, and vaterite in the NaOH experiments and aragonite in the Na2CO3 ones. Thermodynamic modeling results are consistent with these observations and show that alkalinity addition makes seawater supersaturated with respect to all the minerals that are observed to precipitate. Collectively, our data indicate that adding alkalinity to seawater induces the precipitation of various minerals and that the mineralogy of the precipitate is dependent on the form of alkalinity addition (i.e., as NaOH or Na2CO3). Moreover, the precipitate mineralogy changes through time, pointing to a dynamic system characterized by mineral precipitation, dissolution, and transformation. Importantly, determining what minerals form under what conditions is critical to evaluate the efficiency of OAE at sequestering CO2.
How to cite: Hashim, M., Klein, F., Hayden, M., and Subhas, A.: Mineral Formation during Ocean Alkalinity Enhancement Laboratory Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14165, https://doi.org/10.5194/egusphere-egu25-14165, 2025.
The weathering of limestone (CaCO3) by carbonic acid (H2CO3) consumes atmospheric CO2, and due to weathering kinetics that are orders of magnitude faster than silicate rocks, is increasingly seen as a promising enhanced weathering material (Hamilton et al., 2007; Holden et al., 2024). In agricultural settings, however, lime is typically applied to counteract the soil acidifying effects of nitrogenous fertilisers and is therefore thought of as a CO2 source.. In brief, the nitrification of ammonium (NH4+) generates protons (H+) that, when neutralised by CaCO3, can result in direct CO2 emissions (Raza et al., 2021). However, not all nitrogen fertilisers are made equal and the net CO2 impact of lime differs according to fertiliser type and application rate. This study investigated the impact of three common fertiliser types on enhanced weathering outcomes in a 45-pot mesocosm experiment using homogenised loam soil planted with a spring barley crop. In order of most to least acidifying, the fertilisers investigated were protected urea (PU), calcium ammonium nitrate (CAN) and calcium nitrate (CN). In April 2024, lime was applied to ‘treatment’ pots at a rate of 5 tonnes hectare-1 in combination with PU, CAN and CN at two application rates (75 kg N hectare-1 and 150 kg N hectare-1), while lime-only and fertiliser-only pots were established as controls. Leachate samples were collected from the bottom of each pot at bi-weekly intervals over a period of 8-months and measured for pH, total alkalinity, cations and anions to track weathering and CO2 uptake. Cation uptake in the barley crop and on soil exchange sites was measured at the end of the experiment to assess potential CO2 loss pathways. Finally, the dry weight of grain, leaf and stem, from the harvested barley crop was measured to assess the agronomic impacts of different treatment combinations. Preliminary results indicate that while nitrogen application rate had a significant impact on crop yield, neither fertiliser type nor application rate had a significant impact on net CO2 impact.
How to cite: Leet, K., Magee, R., Crehan, L., and Bryson, M.: Investigating the impact of three nitrogen fertilisers on enhanced weathering outcomes with limestone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21723, https://doi.org/10.5194/egusphere-egu25-21723, 2025.
Enhanced Rock Weathering (ERW) has emerged as a promising climate mitigation strategy, with many studies recommending annual application rates of 40–50 tonnes per hectare to maintain high, observable weathering rates. However, our analysis of 23 ERW field deployments reveals that such substantial application volumes may not significantly improve net carbon dioxide removal efficiency and could pose potential ecological risks to farmland and aquatic ecosystems1,2. As an alternative, we propose integrating ERW into urban farming systems as a sustainable carbon dioxide removal (CDR) technology.
Urban farming systems, such as hydroponic and vertical farms, increasingly considered in future food production, offer unique opportunities for ERW deployment3. With 68% of the global population projected to live in urban areas by 20504, these systems are positioned to stabilise food security while supporting climate mitigation efforts. Incorporating ERW into these controlled environments offers several advantages. Unlike conventional field applications, the closed-loop cycling of carbon dioxide and water within urban farming systems enables precise monitoring and adjustment of key variables, including weathering products such as alkalinity and dissolved inorganic carbon (DIC) levels. These parameters can be efficiently tracked using cost-effective Monitoring, Reporting, and Verification (MRV) methods, potentially outperforming traditional field-based MRV methodologies in terms of accuracy and affordability.
This approach not only enhances the carbon dioxide removal efficiency of ERW but also aligns with the sustainable intensification of food production. By integrating ERW into urban farming systems, we propose a novel pathway for simultaneously mitigating climate change and addressing food security challenges.
References:
Calabrese, S. et al. (2022) ‘Nano- to Global-Scale Uncertainties in Terrestrial Enhanced Weathering’, Environmental Science and Technology. Available at: https://doi.org/10.1021/acs.est.2c03163.
Strefler, J. et al. (2018) ‘Potential and costs of carbon dioxide removal by enhanced weathering of rocks’, Environmental Research Letters, 13(3), p. 034010
United Nations(2018). 2018 Revision of World Urbanization Prospects 2018. https://www.un.org/en/desa/2018-revision-world-urbanization-prospects (Accessed: 2025/1/13)
Specht, K. et al. (2014) ‘Urban agriculture of the future: an overview of sustainability aspects of food production in and on buildings’, Agriculture and Human Values, 31(1), pp. 33–51. Available at: https://doi.org/10.1007/s10460-013-9448-4
How to cite: Ouyang, Z. and Redfern, S.: Can Enhanced Rock Weathering become a significant component of Urban Farming? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21583, https://doi.org/10.5194/egusphere-egu25-21583, 2025.
Enhanced rock weathering (ERW) has emerged as a promising carbon dioxide removal (CDR) strategy, with tens of dedicated EW commercial entities having been set up in the last three years. UNDO is one of these, with commercial operations across the Northern United Kingdom and Eastern Canada.
Commercial entities selling CDR, like UNDO, are required to measure, verify and report how much CO2 has been removed at regular time intervals. However, different methods of CDR quantification are likely to produce different numbers, depending on where the measurement has taken place (e.g., soil-based measurement vs a pore-water sample).
We propose an approach that uses pore water concentrations in conjunction with climate data to more robustly estimate CDR per unit area of land, as new pore water data is generated. This approach allows us to estimate the amount of charge-balanced bicarbonate/carbonate ions that are transported past a certain depth point.
Furthermore, our method is compared against other indicators of weathering processes, such as exchangeable cations and carbonate precipitation. For these calculations and comparisons, we will use data from a field trial that has been running for 2 years.
How to cite: Liu, X., Skov, K., Stubbs, A., Betz, J., Wade, P., Albahri, T., Cazzagon, G., Healey, M., Radkova, A., Solpuker, U., Turner, W., and Wardman, J.: Quantifying Carbon Dioxide Removal using Pore Water Data from Enhanced Rock Weathering Field Trials in Scotland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20138, https://doi.org/10.5194/egusphere-egu25-20138, 2025.
Enhanced rock weathering is a promising carbon removal technique that uses the natural process of silicate minerals weathering to capture atmospheric CO₂. This research investigates the relationships between soil texture and the dynamics of basalt-enhanced rock weathering products in a controlled mesocosm experiment. Mesocosms were constructed with three soils of distinct textures: sandy silty loam, sandy loam, and clay, each treated with 0-4 mm crushed basalt rock at an application rate of 100 tons per hectare, alongside control treatments. The duration of the experiment is one year, with pore water collected biweekly using rhizon samplers at depths of 10 cm and 20 cm, as well as leachate samples taken from 30 cm at the bottom of the cores. The crop grown on the soil mesocosms was perennial rye grass at a seeding rate similar to agronomic best practice densities. Results from the experiment include a comprehensive analysis of pore water, solid soil samples (after termination of the experiment), as well as crop uptake. The results indicate that basalt weathering is happening in amended samples compared to control mesocosms across all soil types, however with different responses in pore water concentrations between each soil type. Towards the end of the experiment clear differences between treatment and control are observed in the pore water concentrations of cations in the sandy and loamy soil types, whereas the concentration of cations appears to be similar in the clayey soil type. The variation in response is likely driven by the water retention capacity and cation exchange capacity of each soil type. Understanding the patterns for each soil type is important for accurately measuring MRV and evaluating carbon capture potential in different environments. This research provides an important empirical understanding that can aid in advancing weathering predictions through geochemical models.
How to cite: Cazzagon, G., Skov, K., Radkova, A., Frew, A., Stubbs, A., Healey, M., Chen, E., Harrity, S., Agace, K., Liu, X., and Bierowiec, T.: The Impact of Soil Texture on Basalt-Enhanced Rock Weathering: Insights from a Field Mesocosm Study in a Temperate Climate., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19914, https://doi.org/10.5194/egusphere-egu25-19914, 2025.
Enhanced rock weathering is a promising carbon dioxide removal (CDR) technology that involves the dissolution of silicate minerals (e.g., wollastonite). This process releases elements such as calcium, which can remain in solution and be charge balanced by bicarbonate, or be stored as pedogenic carbonate or on soil exchange sites. To verify carbon removal credits, robust monitoring, reporting, and verification (MRV) approaches are essential. In this study, we explore total cation accounting (TCA) as a novel method for MRV. TCA involves conducting a total digest of a soil-feedstock mixture in the near-field zone (NFZ; here defined as 15 cm) and analysing the major cation content via Inductively Coupled Plasma Optical Emission Spectroscopy. The resulting data include baseline cations in the soil (pre-spread), residual feedstock (post-spread), and weathered cations bound to exchange sites or forming carbonate minerals (post-spread). The major cations (Ca, Mg, K, Na) are summed to calculate total cations, and net cation loss from the NFZ is used to determine CDR.
This study uses data from a small plot monitoring site (SPMS; 4x10 m) in Ontario, Canada, where Canadian Wollastonite feedstock was applied at four different densities (0, 5, 50, and 100 t/ha) in November 2023. Soil samples were collected across the SPMS using a 20:1 composite of 15 cm soil cores. The soils were finely crushed to preserve the distribution of larger feedstock particles, ensuring homogeneity and maintaining a representative soil-to-feedstock ratio.
Prior to spreading, cation concentrations in both treatment and control groups were clustered around a similar mean, representing the baseline soil composition. Samples collected post-spread show an increase in cation content on treatment plots, demonstrating that the addition of our feedstock is resolvable, even in settings with unusually high background soil Ca content. All subsequent samples show cation content decreasing relative to the post-spread levels, indicating cations have been exported into the far-field zone (FFZ) or lost via plant uptake or solid transport. The results are consistent with other MRV approaches applied on the same field trial, although our results suggest that other methods can underestimate CDR. One advantage of TCA over competing MRV methods is that the results are time-integrative, meaning the signal-to-noise ratio improves with longer sampling intervals. These first field trials using this approach demonstrate its potential as a scalable, robust methodology for MRV in ERW trials.
How to cite: Stubbs, A., Tostevin, R., Healey, M., Skov, K., Turner, W., Cazzagon, G., Albahri, T., Bierowiec, T., Jones, L., Couillard, Z., Couillard, J., Stadtke, C., Janfield, G., Wisteard, L., DeJordy, D., Chaput, D., and Liu, X.: Evaluating Total Cation Accounting (TCA) as an MRV Approach for Enhanced Rock Weathering - Insights from a trial in Ontario, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18780, https://doi.org/10.5194/egusphere-egu25-18780, 2025.
Keywords: Enhanced Rock Weathering, Carbon Dioxide Removal, Life Cycle Analysis, Sustainable Supply Chain, Southeast Asia
Enhanced Rock Weathering (ERW) carbon credit development practices have predominantly been conducted in non-tropical regions, often hindered by the lack of robust Measurement, Reporting, and Verification (MRV) methodologies. In response to the pressing demand for scalable and durable carbon removal solutions, this research investigates the deployment of ERW on agricultural land in Southeast Asia to generate high-quality carbon credits. Using Life Cycle Analysis (LCA) to assess emissions and Techno-Economic Analysis (TEA) for credit generation, we evaluated key processes including feedstock processing, transportation, deployment, MRV, and post-application activities. Addressing debates surrounding the potential overestimation of ERW’s carbon removal capabilities, we incorporated MRV into the credit life cycle—a component surprisingly overlooked in existing literature despite its substantial contribution to emissions and costs. Furthermore, our study goes beyond conventional carbon offsetting by integrating ERW within supply chains to enable carbon insetting, offering added benefits to both upstream and downstream stakeholders. Ultimately, this research lays a critical foundation for refining ERW carbon credit methodologies by improving Scope 3 emissions quantification, thereby advancing sustainable supply chains and contributing to global climate mitigation objectives.
How to cite: Zhang, Y. and Redfern, S.: Potentials of Enhanced Rock Weathering (ERW) Carbon Insetting in Southeast Asia to Form a More Sustainable Supply Chain: Life Cycle Analysis and Techno-Economic Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18551, https://doi.org/10.5194/egusphere-egu25-18551, 2025.
Multiple measurements can be used to quantify the carbon dioxide (CO2) captured during enhanced rock weathering (ERW) applications. In most terrestrial applications, CO2 is dominantly stored as carbonate alkalinity inside the water. Total alkalinity (TA) is often taken as a measure of the CO2 stored in the water. However, the contribution of acids other than carbonic acid to mineral dissolution and, thus, to the generated alkalinity must be studied closely to reliably quantify CO2 capture.
In this study, we test how dissolved organic carbon (DOC) impacts non-carbonate alkalinity and the charge balance error of leached waters from a microcosm experiment using organo-mineral mixtures under ambient conditions. Furthermore, we quantified the concentrations of several low-molecular-weight organic acids to assess which conjugate base anions impact TA.
Our results reveal a substantial contribution of DOC to non-carbonate alkalinity, yielding a ratio of 3.5 mol DOC per eq of non-carbonate alkalinity. Moreover, we found a positive correlation between DOC levels and charge balance error, indicating that some of the conjugate base anions of the organic acids remained deprotonated in the titration procedure. Acetate anions found in the DOC-rich water samples further support the notion that organic acids have impacted mineral dissolution. The microcosm experimental data show parallels to natural ERW processes in organic-rich soils, demonstrating that organic acid contributions are relevant in mineral dissolution dynamics. These insights are relevant for carbon accounting in terrestrial ERW practices, where TA is often assumed to be solely carbonate alkalinity despite varying environmental conditions.
How to cite: Rieder, L., Hagens, M., Poetra, R., Vidal, A., Calogiuri, T., Neubeck, A., Singh, A., Corbett, T., Niron, H., Vicca, S., Vlaeminck, S., and Hartmann, J.: Contribution of dissolved organic carbon to total alkalinity , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18005, https://doi.org/10.5194/egusphere-egu25-18005, 2025.
There is currently no consensus in the literature as to whether the mineralogical composition and theoretical weatherability or grain size and surface area of feedstock materials used for carbon capture via enhanced rock weathering are stronger determinants of weathering rates of silicate minerals applied to agricultural soils. Felsic source rocks have typically been discounted for enhanced rock weathering in favor of more easily weatherable mafic and ultramafic rocks. However, previous work has indicated that Greenlandic glacial rock flour, a potential feedstock with an exceedingly fine grain size (d50 = 2.6 µm) but a felsic composition, can weather at sufficiently rapid rates to be effective for carbon capture and improving crop yields through the release of nutrients during weathering. Here we present initial experimental results comparing the use of Greenlandic glacial rock flour and several sources of basaltic material as feedstocks for enhanced rock weathering. Two field trials installed in Ghana and South Carolina demonstrate the varying effects of these materials on maize yield, and two flow-through laboratory experiments, one with plants and one without, assess the differences in alkalinity generation and cation release between these feedstocks over time. Among the tested basalts, chemical composition seems to be a stronger driver of weathering rates than differences in grain size. However, none were as finely ground as the glacial rock flour, which was found to weather at a rate comparable to or, in some cases, higher than the basaltic materials, despite being composed of less chemically reactive minerals. These results suggest that mineral weatherability is an important predictor of weathering rates, but with a large enough difference in grain size the amount of surface area available for reaction can be equally important.
How to cite: Dietzen, C., Barton, F., Oppong Danso, E., Foster, D., Hammes, J., Rizzi, M., and Rosing, M.: The relative importance of grain size and mineral weatherability for enhanced rock weathering rates: a comparison of glacial rock flour and basaltic feedstocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16173, https://doi.org/10.5194/egusphere-egu25-16173, 2025.
Enhanced rock weathering - the introduction of alkaline minerals into agricultural soil - is a promising atmospheric carbon dioxide removal technology that could scale to billions of tonnes of carbon sequestration annually. However, many questions remain over the speed and magnitude of ERW’s efficacy and the longer term consequences of repeated rock dust applications for sustained carbon removal, soil health benefits, and improved crop yields. A number of studies have tested the effect of alkaline mineral additions under field settings, indicating potential for CDR and improved cropping conditions and soil properties. These studies were performed for one to a few years, however global ERW potential will require applications over the majority of Earth’s croplands for decades. Here we present the results from the initial two years of a ten year trial, The Decade Experiment, involving ERW with metabasalt (CaSiO3, MgSiO3) in cropland soil planted with Zea mays (field corn) in upstate New York. We also present results from agriculture lime additions in the same setting to ascertain the differences between ERW with silicate rocks vs. direct carbonate rock additions. The study was initiated over three acres in 2023 following a systematic step-down model whereby rock dust amendments will be applied annually for up to ten years, with individual rows spanning between zero (control conditions) to ten years of annual rock dust amendments. This entails plots receiving only one year of amendment, followed by two years, traversing all annual increments to ten years of annual rock dust additions for the final plots. With this approach we seek to investigate the effects of single rock dust additions compared to multiples of years of amendments systematically spanning a full decade of continuous measurements from all treatments.
Carbon dioxide removal was examined by extracting soil pore water with negatively pressurized porous ceramic lysimeters. Lysimeters were installed at two depths, 15 cm and 30 cm, and continuously monitored over the 2023 and 2024 growing season, with 1192 samples collected across all treatments. Measured dissolved inorganic carbon (DIC) and calculated alkalinity of the soil pore water were used to determine carbon removal efficiency, since the initial step in weathering involves silicate minerals reacting with dissolved CO2 to form bicarbonate following Holzer et al. 2023. Bicarbonate concentrations of soil pore waters increased by 10% in the two year amended plots compared to control at the 15 cm sampling depth. Soil pH and cation exchange capacity (CEC) were higher on average in amended soils compared to untreated controls, indicating soil chemical transformation due to ERW. Yield of Zea mays was observed to increase in plots amended with 44.8 t/ha for two years relative to control and the plot only treated for one year. Metabasalt amendments increased yields with repeated application, improved soil quality, and sequestered carbon. These initial two year results will continue to be explored over the next ten years to understand the long-term consequences of ERW, including benefits and risks for carbon removal, soil health and crop yields in The Decade Experiment.
How to cite: Evans, C., Meagher, S., Tsai, C.-H., and Houlton, B.: “Long effects of enhanced rock weathering: the first two years of The Decade Experiment”, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13189, https://doi.org/10.5194/egusphere-egu25-13189, 2025.
Achieving targets of net-zero carbon emission requires a large-scale drawdown of carbon dioxide from the atmosphere. A sustainable solution provided through rock weathering of silicate and carbonates at glaciers has shown some carbon drawdown potentials, yet we still lack to fully understand this natural process for mitigating climate change. Conventional view of rock weathering recognizes carbonic acid mediated weathering of silicate and carbonate minerals as CO2 sink, yet we emphasize that weathering of sulphur bearing minerals (i.e., FeS2) counterbalance this CO2 sink for mountain glaciers. We studied the Dokriani glacier basin, central Himalaya as model system for long-term (1992-2018) and tested the CO2source or sink mechanism. Our results suggest a clear trend of CO2 release from Himalayan glaciers. Results suggests atmospheric CO2 sink driven through carbonic acid-mediated reactions during the early ablation periods, while a clear CO2 source through sulfuric acid-mediated reactions superseding the CO2 sinks during peak and late ablation periods was observed. The former tips the balance of the CO2 budget of the Himalayas from sink-to-source. The other glaciers of the central and western Himalayas are in good agreement with the present estimates. We surmise that these patterns are broadly applicable to the other orogenic systems of the world. These findings enhance our understandings for CO2 release potentials of mountain glaciers through glacial weathering, atmosphere and terrestrial systems.
How to cite: Shukla, T.: Carbon release potential from enhanced sulfuric acid-mediated weathering is alarming for retreating Himalayan glaciers , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8178, https://doi.org/10.5194/egusphere-egu25-8178, 2025.
Enhanced rock weathering (ERW) is emerging as a promising scalable carbon dioxide removal (CDR) strategy. However, the lack of methods for in situ quantification of rock weathering currently limits the ability to monitor, verify, and report CDR via ERW. Given the technical challenges of durable carbon sequestration in heterogeneous ecosystems where ERW is applicable, accurate and reliable validation of ERW is essential. Therefore, we propose a novel aqueous-phase extraction approach, the centrifugation pore water extraction sampling method, to obtain and analyse soil pore waters. Using a large-scale, replicated field trial of ERW combined with tree planting at an afforestation site in mid-Wales, we demonstrate that soil centrifugation provides a reliable method for extracting pore water necessary for accurate CDR estimations. This method was particularly effective during periods of low precipitation and associated low soil water content when conventional aqueous-phase methodologies fail to obtain sufficient pore water samples. Additionally, soil centrifugation provided estimates of potential CDR by analysing weathering products accumulating within soil micropores, an aspect not adequately addressed by conventional aqueous-phase methodologies.
How to cite: Jones, G., Zhang, Z., Clayton, K., Paschalis, A., and Waring, B. G.: Utilising soil centrifugation for accurate carbon dioxide removal estimates via enhanced rock weathering , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11872, https://doi.org/10.5194/egusphere-egu25-11872, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-14511 | ECS | Posters virtual | VPS4
A flexible, multiscale quantification framework for river alkalinity enhancementWed, 30 Apr, 14:00–15:45 (CEST) | vPA.26
Alkalinity enhancement in rivers is a proposed carbon dioxide removal strategy which leverages physical and biogeochemical properties of rivers to promote uptake of atmospheric carbon dioxide. Robust monitoring, reporting and verification of carbon dioxide removal is necessary to instill trust in carbon credits and market activity stemming from river alkalinity enhancement. Rivers have the unique characteristic of reflecting integrated watershed characteristics along a one-dimensional trajectory. Depending on the size of the river, alkalinity dosing location and quantity, transit distance to the ocean and availability of monitoring locations, carbon dioxide uptake can be quantified through a hybrid approach leveraging direct measurements and models. In this poster, we propose a flexible, multiscale quantification framework which can be adapted to a wide range of rivers and deployment scenarios.
How to cite: Yin, J., He, J., Sutherland, K., and Gill, S.: A flexible, multiscale quantification framework for river alkalinity enhancement, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14511, https://doi.org/10.5194/egusphere-egu25-14511, 2025.
