Less is more: how to capture carbon efficiently – lessons from long-term rock weathering and soil development in natural warm temperate ecosystems.

Dimitar Z. Epihov 

Enhanced rock weathering (ERW) has been proposed as a viable strategy to offset greenhouse gas emissions. The field is currently plagued by uncertainty in the rates of C capture through alkalinity export, resulting from variation in extent and lag due to soil exchange, secondary minerals, and effects on soil organic carbon. Provided are quantitative estimates for weathering losses in these pools using a natural weathering system on a volcanic rock hill, Bulgaria. Two distinct soils are compared: mafic soils derived predominantly from cation-rich basalt (81–85%) with minor dacite (~15–19%), and felsic soils (66% dacite, 34% basalt). Major cations were partitioned into four pools: primary minerals, exchangers, clays, and leached. Leaching accounted for 34% of total cations in felsic soils and 12% in mafic soils. Exchangers and clays accounted for ~50% of all cations in felsic soils compared to 25% in mafic soils. Only 16% of cations remained in primary minerals in felsic soils versus 62% in mafic soils. Goethite peaked in felsic soils and correlated with ~2-fold larger soil organic carbon stocks than in mafic soils. These findings suggest that CO₂ removal potential in ERW may be overestimated, and that smaller basalt applications may more rapidly boost inorganic and organic C capture.