Industrial carbon input to arable soil since 1958. (March 2015) - Lehndorff, Eva
Graphical abstract: Highlights: 14 C analysis of benzene polycarboxylic acids traced fossil black C (BC) deposition. In soil 75% of total BC originated from fossil fuel combustion. Fossil BC accumulated at a rate of 9 g/m 2 yr from 1958–1971. No additional accumulation of fossil BC after 1971 detected. Fossil BC appeared stable in soil. Abstract: Tracing the history of industrial fossil fuel combustion on the carbon stock in soil is challenging, since it is mixed with other soil organic carbon (SOC). Isolation of black carbon (BC) yields a mixture of diagenetic fossil C and pyrogenic BC from biomass and fossil fuel combustion. We investigated the degree to which fossil fuel combustion emissions have contributed to SOC and BC and how deposition dynamics have changed in the last century. As only biomass-derived BC contains 14 C, we determined the content and 14 C signature of the benzene polycarboxylic acid (BPCA) fraction as the product of total BC oxidation. From an isotopic mass balance model, the proportion of fossil BC deposition and its contribution to SOC was calculated. Soil samples were taken from 1958–2002 from a long term agricultural field experiment in Halle, Germany; the area represents one of the most productive lignite mining areas in the world. Between 1958 and 1971, total BC content increased significantly (1.9 ± 0.1–2.30 ± 0.06 g/kg soil), and the BC-specific radiocarbon content decreased from 29.6 ± 0.4 to 26.9 ± 0.2 pMC, corresponding to 1.35 ± 0.07 and 1.8 ± 0.08 g/kg BC from diagenetic C and fossil fuel combustion (denoted here as fossil BC). We infer an increase in fossil BC content of 30% within this timespan, with a net input rate of 9 g/m 2 yr. In the 1970s, after railway electrification, reduction of lignite mining and related heavy industries, fossil BC deposition to soil was no longer significant. Overall, about 120 g/m 2 fossil BC was deposited between 1958–1971, with 390 g/m 2 before 1958. Fossil BC contributed ca. 75% of total BC and 15% SOC to arable soil, without any significant change in the following 30 yr (1971–2002).