Abstract
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 °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 CO2 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 CO2 ha−1 sequestered into the soil.
Highlights
The Intergovernmental Panel on Climate Change (IPCC) has highlighted the need for CO2 removal in avoiding a rise in global temperature more than 1.5 °C relative to pre-industrial times (IPCC, 2018)
CASPER has been used initially to simulate an artificial soil of 1 ha of dolerite substrate which was mixed with an equal volume of green compost down to 1 m depth, over a period of 5 years (Manning et al, 2013)
C sequestration through land management may be extended from a focus on organic decomposition to encompass the various effects of inorganic carbon precipitation, with the intention of creating an increased store of stable inorganic C
Summary
The Intergovernmental Panel on Climate Change (IPCC) has highlighted the need for CO2 removal in avoiding a rise in global temperature more than 1.5 °C relative to pre-industrial times (IPCC, 2018). A number of models are available to predict changes in SOC in space and time, with relevance to planning land use and soil management. These models account in a simplified way for the turnover and stabilisation that occurs during decomposition, in response to plant productivity, climate and soil texture. Examples of such models include Roth C, CENTURY (Paustian et al, 1992; Parton, 1996) and DAISY (Mueller et al, 1996). Development of the CASPER model should permit integrated approaches to land management for C storage, where the supply of calcium from mineral sources is managed in order to promote precipitation of the carbonate mineral calcite (CaCO3)
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