Methods of inorganic carbon removal from aridisols: Implications for quantifying organic carbon pools in arid ecosystems

Measuring soil organic carbon (C) is critical for quantifying pools of terrestrial C and modeling C cycling. In order to measure organic C by dry combustion, inorganic C must first be removed from the soil. Several methods for removing inorganic carbon by acid pre-treatment are currently accepted in the literature and are used interchangeably despite documented differences in their impact on organic C, nitrogen (N) and stable isotope composition. Rarely are these methods optimized and are assumed to work equally well on soils with wide ranging amounts of inorganic C. Stable isotopes are a powerful tool for understanding the effectiveness and bias of these different methods. Inorganic C as carbonate has a δ¹³C ranging from -2 to 2‰ while organic soil C usually has a δ¹³C of -15 to -30‰. The δ¹³C of soil is therefore a mixture of these two pools and small changes in the pools of inorganic or organic C can affect δ¹³C. Inaccurate measurements of these pools can affect the interpretation of δ¹³C of organic matter and affect %C measurements. Here, we analyze the removal of inorganic C of aridisols from the Mojave Desert using four methods (0.5 M HCl, 6 M HCl, 1 M H₃PO₄ and HCl fumigation).