Abstract
The proportions of different carbon pools within artificial soils prepared by blending composts with dolerite and basalt quarry fines has changed over a period of 7 years, accumulating inorganic carbon as carbonate minerals newly formed within the soils. With no artificial energy inputs following construction, this is regarded as a passive mineral carbonation process. Carbon isotope data show that up to 40% of the carbon within the soil carbonate is derived from photosynthesis, mixed with carbon from geological sources (limestone present in the quarry fines). Organic matter within the soils shows very variable composition, with an apparent increase with time in the relative proportion of labile carbon relative to more stable forms, reflecting a change in the soil organic matter composition associated with the establishment of new plant communities. The rate of accumulation of inorganic carbon as carbonate minerals is estimated to be equivalent to 4.8tCha−1 annually to a depth of 0.3m, consistent with rates observed for accumulations of carbonate carbon in urban soils containing demolition wastes (annually 3.0tCha−1 to 0.3m). There appears to be substantial potential for artificial soils to be designed expressly for the purpose of carbon capture. The process is analogous to the use of reed beds for the removal of pollutants from contaminated waters.
Highlights
There is little doubt that atmospheric concentrations of CO2 and other greenhouse gases have increased as a consequence of human activity, possibly dating back to the dawn of agriculture (Kutzbach et al, 2010) as well as through the comparatively recent combustion of fossil fuels since the industrial revolution (Denman et al, 2007)
Restoration of organic carbon concentrations in modified soils has the potential to be an important tool for mitigating anthropogenic climate change (Lal, 2003), as long as organic inputs are maintained to compensate for turnover
In the context of considering ways in which soils can be managed to enhance the accumulation of inorganic carbon derived from the atmosphere, this paper describes artificial plots that have developed significant pedogenic carbonate within a blend of compost and finely ground basic igneous rock
Summary
There is little doubt that atmospheric concentrations of CO2 and other greenhouse gases have increased as a consequence of human activity, possibly dating back to the dawn of agriculture (Kutzbach et al, 2010) as well as through the comparatively recent combustion of fossil fuels since the industrial revolution (Denman et al, 2007). In the context of climate change mitigation, there is a need to improve our understanding of natural processes that remove atmospheric CO2 in ways that begin to compensate for artificial emissions Work of this type provides a basis for decisions to be made that enable sustainable carbon dioxide removal systems to be trialled, and possibly implemented. Restoration of organic carbon concentrations in modified soils (agriculture and urban environments) has the potential to be an important tool for mitigating anthropogenic climate change (Lal, 2003), as long as organic inputs are maintained to compensate for turnover. The work presented in this paper augments reports of carbonation of synthetic calcium silicate minerals (Renforth and Manning, 2011), and is significant because the carbonation of natural calcium silicate minerals through ‘enhanced weathering’ within soils could, by virtue of their widespread natural occurrence, be much more significant (Schuiling and Krijgsman, 2006; Hartmann and Kempe, 2008; Hartmann et al, 2013; Köhler et al, 2010; Renforth, 2012)
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