How does acid treatment to remove carbonates affect the isotopic and elemental composition of soils and sediments?

In the present work, we compared the efficacy of three acid treatments in removing carbonates from soils and sediments for elemental and isotopic analysis. The methods tested were (1) refluxing with H2SO3; (2) in situ treatment with H2SO3 in silver capsules; and (3) treatment with HCl followed by rinsing with water. Refluxing with H2SO3 led to substantial losses of organic carbon and nitrogen, but comparatively small nitrogen isotopic shifts. The in situ treatment was inadequate for carbonate-rich samples (contents >= 30%) as a consequence of the formation of a mineral precipitate. Treatment with HCl led to substantial losses of nitrogen from carbonate-rich samples, and deviations in nitrogen isotopic signatures (delta N-15) of up to 3.7%. delta N-15 values showed no significant difference between acid-treated and untreated samples or between treatments, although variability was high and influenced by sample composition. Carbonate-poor samples showed no statistical difference in delta C-13 values between treatments, whereas carbonate-rich samples tended to be more C-13-depleted when treated with HCl, potentially suggesting the preferential preservation of C-13-depleted compounds (e. g. lipids or lignin).