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Using Hg stable isotope ratios to trace the bioaccumulation of Hg in the lower food web of Lake Erie
Citation:
Lepak, R., S. Janssen, D. Krabbenhoft, J. Ogorek, J. DeWild, M. Tate, AND J. Hurley. Using Hg stable isotope ratios to trace the bioaccumulation of Hg in the lower food web of Lake Erie. International Conference of Great Lakes Research, Brockport, NY, June 10 - 14, 2019.
Impact/Purpose:
Mercury is a neurotoxic metal capable of bioaccumulation in aquatic ecosystems and the Great Lakes are susceptible to contamination. Scientists currently do not adequately understand the process that leads to bioaccumulation of Hg into the lower food web and which sources of Hg hold the greatest propensity for bioaccumulation. Therefore, we participated on the first ever mercury tracer study on the lower food web in the Great Lakes by measuring particulate matter, seston and water in open Lake Erie and major tributaries to the lake.
Description:
In aquatic ecosystems, the use of mercury (Hg) stable isotopes to identify Hg sources has typically focus on identification of point and non-point sources in sediments, with the assumption that sediments were primary sources of bioaccumulative methylmercury (MeHg). We measure Hg stable isotopes in the suspended particulate matter (SPM), water, planktonic material of Lake Erie, and from surrounding watershed inputs to better understand the relative availability of contrasting Hg sources for bioaccumulation. Tracers for mass dependent and independent isotopic fractionation suggest contrasting Hg source portfolios for SPM and filtered water in both inflowing rivers and open water. Riverine SPM resembled terrestrial soils, and western Lake Erie sediments, while open lake SPM, primarily comprised of planktonic material resembled atmospheric Hg with isotopic signatures linked to the fraction of MeHg in planktonic material. This allowed calculation of ä202Hg and Ä199Hg for the source inorganic Hg and epilimnetic MeHg, useful for determining dynamics associated with recently deposited Hg. Large Ä200Hg in planktonic material highlights the importance of recently deposited Hg from atmospheric precipitation. These results decouple Hg sources to the lower trophic epilimnetic food web from Hg to the sediments, highlighting the relative importance of atmospheric and watershed-sourced Hg to biota.