Determination of the Concentration and Isotopic Composition of Soil Carbon in Arid Soils

Abstract

Core Ideas Measurement of inorganic and organic C in arid soils can be challenging. Acid dissolution does not affect amount and isotopic composition of organic C. Loss on ignition is unreliable when measuring isotopic composition of inorganic C upon heating. Accurate quantification of organic C (OC) and inorganic C (IC) in arid soils is critical given that arid lands make up a substantial part of the terrestrial surface and IC is often the dominant C pool. Two methods were tested to quantify the percent OC and IC and the 13C isotopic composition on soils prepared by mixing a carbonate‐free surface soil with a ground marble tile achieving varying ratios of OC versus. IC. The loss on ignition percent C and δ13C data showed that at 400°C not all organic C was volatilized making this method unreliable at higher OC fractions. Additions of 1M HCl did not alter the amount and isotopic composition of the OC regardless of the relative amounts of OC versus IC present. Overall, the best method for measuring soil C concentration and δ13C depends on the relative concentrations of OC versus IC that are present in the soil.