Arsenic in lake sediments: Resolving historical deposition from biogeochemical transformation

GEOC 27

Philippe Van Cappellen, pvc@eas.gatech.edu1, Babak Shafei1, Raoult-Marie Couture2, Charles Gobeil2, and André Tessier2. (1) School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0340, (2) INRS-ETE, Université du Québec, 490 Rue de la Couronne, Québec, QC G1K 9A9, Canada
The fate and transport of arsenic in the environment is strongly influenced by microbially mediated transformations of iron minerals. In this study, a reactive transport model is used to simulate the early diagenesis of arsenic in sediments of a Canadian lake. The model accounts for the biogeochemical reactions that control the coupled redox cycles of carbon, oxygen, nitrogen, sulfur, iron, and arsenic. The results indicate that the depth profile of sediment-bound arsenic reflects not only past changes in arsenic supply to the sediments, but also the redistribution of arsenic between iron(III) oxyhydroxide and iron(II) sulfide phases. Ignoring the latter leads to an erroneous interpretation of the historical deposition of arsenic to the lake.