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Factors affecting mercury stable isotopic distribution in piscivorous fish of the Laurentian Great Lakes

February 15, 2018

Identifying the sources of methylmercury (MeHg) and tracing the transformations of mercury (Hg) in the aquatic food web are important components of effective strategies for managing current and legacy Hg sources. In our previous work, we measured stable isotopes of Hg (δ202Hg, Δ199Hg, and Δ200Hg) in the Laurentian Great Lakes and estimated source contributions of Hg to bottom sediment. Here, we identify isotopically distinct Hg signatures for Great Lakes trout (Salvelinus namaycush) and walleye (Sander vitreus), driven by both food-web and water-quality characteristics. Fish contain high values for odd-isotope mass independent fractionation (MIF) with averages ranging from 2.50 (western Lake Erie) to 6.18‰ (Lake Superior) in Δ199Hg. The large range in odd-MIF reflects variability in the depth of the euphotic zone, where Hg is most likely incorporated into the food web. Even-isotope MIF (Δ200Hg), a potential tracer for Hg from precipitation, appears both disconnected from lake sedimentary sources and comparable in fish among the five lakes. We suggest that similar to the open ocean, water-column methylation also occurs in the Great Lakes, possibly transforming recently deposited atmospheric Hg deposition. We conclude that the degree of photochemical processing of Hg is controlled by phytoplankton uptake rather than by dissolved organic carbon quantity among lakes.

Publication Year 2018
Title Factors affecting mercury stable isotopic distribution in piscivorous fish of the Laurentian Great Lakes
DOI 10.1021/acs.est.7b06120
Authors Ryan F. Lepak, Sarah E. Janssen, Runsheng Yin, Jacob M. Ogorek, David P. Krabbenhoft, John F. DeWild, Michael T. Tate, Thomas M. Holsen, James P. Hurley
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Science & Technology
Index ID 70201147
Record Source USGS Publications Warehouse
USGS Organization Upper Midwest Water Science Center