Historical atmospheric deposition in a Swedish mining area traced by S isotope ratios in soils

Mining activities for almost thousand years have caused large S emissions i n the Falun area, central Sweden. Since the beginning of the 20th century, the S deposition has decreased considerably. The soil S concentrations and S isotope compositions were analyzed for CS and adsorbed SO42- for three so il profiles close to the mining area in order to identify the soil S source s. The delta(34)S values were found to be different for CS and adsorbed SO4 2- and ranged from -3.7 parts per thousand to +2.6 parts per thousand. In t he B-horizon, the observed Sigma S delta(34)S values (and hence calculated delta(34)S values for organic S) were mostly lower than those of the absorb ed SO42-. In the O-horizon, Sigma S showed similar delta(34)S values as the adsorbed SO42- in the mineral soil. The adsorbed SO42- showed nearly const ant delta(34)S values with depth. The delta(34)S values in the soils are in terpreted to reflect a mixture of historical and modem deposition due to so il S circulation with no or negligible fractionation. The lower delta(34)S values of organic S in the B-horizon suggests preservation of acid depositi on originating from mining activities back in time. The adsorbed SO42- in t he mineral soil and the organic S in the O-horizon reflect a response to a new delta(34)S composition in the atmosphere due to fossil fuel burning dur ing the 20th century.