Assessing the Impact of Enhanced Rock Weathering on Soil Biological Interactions with Comprehensive Carbon Dioxide Removal Index

Enhanced Rock Weathering (ERW) is emerging as a promising Carbon Dioxide Removal (CDR) strategy. While existing research predominantly measures dissolved inorganic carbon (DIC) and soil inorganic carbon (SIC) to evaluate CDR effects, the significance of plants and their influence on soil organic carbon (SOC) within the ERW process remains underexplored. Our study aims to investigate the impact of ERW amendments on SOC sequestration when applied to soils with planted vegetation. The variation in SOC sequestration due to ERW depends on factors such as the composition of ERW materials, soil conditions, and the presence of plants and microorganisms. Under these interactions, stable SOC storage for at least several decades needs to be considered a CDR effect, although the increase in plant growth may not be considered a CDR effect due to the short carbon storage time. Additionally, we propose the inclusion of non-CO₂ greenhouse gas emissions, particularly N₂O emissions resulting from microbial activity changes, in our comprehensive CDR Index. Here, we suggest a comprehensive CDR Index for ERW, encompassing direct effects on SIC and DIC, indirect impacts on SOC, and N₂O fluxes. To thoroughly investigate the CDR impact of ERW materials, we assessed the CDR Index for two distinct ERW materials: natural rock and industrial by-product silicate. Our four-month pot experiment involved control and two ERW amendments(olivine and blast furnace slag) alongside two planting scenarios(with alfalfa and without plants). We hypothesize that the CDR effect calculated using our comprehensive CDR Index will differ from that calculated using only DIC or SIC measurements. We anticipate significant increases in SIC and DIC for treatments, particularly with blast furnace slag due to its composition. In the plant-involved treatments, we anticipate both higher SIC, as plants accelerate weathering with their acidic exudates, and increased SOC, indicating improved plant growth and subsequent carbon sequestration. Variations in N₂O fluxes are also anticipated with different ERW amendments. Initial data from three weeks shows significant DIC increases with blast furnace slag and modest increases with olivine. Greater plant biomass was observed in treatments compared to control, suggesting varied biological impacts. Throughout the remaining four-month experiment, we aim to document changes in SIC, DIC, SOC, and differences in N₂O fluxes. These results are anticipated to vary based on the type of amendment and the planting options. This research is expected to underscore the significance of the biological effect in a comprehensive CDR assessment and contribute to identifying the most effective conditions for CDR with ERW when considering biological impacts. The findings are expected to guide future research and the implementation of ERW strategies, contributing to global climate change mitigation efforts.