CASPER: A modelling framework to link mineral carbonation with the turnover of organic matter in soil

Rapid formation of stable soil carbonates offers a potential biologically-mediated strategy for removing atmospheric CO2 and forms a part of the negative emissions debate in a bid to maintain global temperatures of 1.5 degrees C. Microbial respiration in soil and respiration by plant roots leads to high partial pressure of CO2 below ground. Given adequate supply of calcium in soil solution the sequestration of C into the mineral calcite (CaCO3) can occur at rapid rates. We have coupled an established soil C model RothC to a simplified geochemical model so that this strategy can be explored and assessed by simulation. The combined model CASPER partitions CO(2 )respired belowground into soil solution as HCO3- and simulates its reaction with Ca2+ based on a particular dissolution rate for Ca-bearing minerals, with precipitation of calcite into soil pores as a consequence. Typical model output matches observed field rates of calcite accumulation over 5 years, namely 81 t ha(-1), with 19 t CO(2)ha(-1) sequestered into the soil.