| Recent advancements in utilizing high precision isotope analysis allows us to trace sources of mercury (Hg) and processes it undergoes without the need of enriched isotope amendment. Here, we use total mercury (HgT) stable isotope ratios in fish, the lower food web, particulate matter, and water to unravel the linkages between bioaccumulation of MeHg and sources of Hg to fish from the Great Lakes and remote Alaska. Through the combination of multiple traditional Hg measurements and Hg stable isotopes, we identify sources of Hg to biota, but also quantify the impact of variables (such as dissolved MeHg concentrations, distribution coefficients, fish age) often absent in Hg isotope studies. This knowledge is critical to interpreting challenging fractionation patterns in fish. In choosing ecosystems absent of point source contamination, we are able to explore background conditions and infer novel processes (e.g. water column methylation) previously unrecognized by applying sensitive isotopic tracers (e.g. Delta200Hg).;We studied ecosystems absent of significant sedimentary MeHg fluxes, and find evidence contrary to the assumption that sediments accurately predict Hg sources to fish. To do so, we use carefully chosen ecosystems and employ the use of intensive water column profiling. With the first use of a biological archive, using Hg stable isotope analysis we probed the impact of Hg mitigation strategies on both sediments and fish, and find that fish respond to Hg mitigation much more rapidly than previously recognized. This, paired with the first lower food web exploration using Hg stable isotopes, supports the notion that sediment Hg and fish Hg concentrations are decoupled. Recently deposited atmospherically-sourced Hg is shown to be highly bioavailable, and fish respond rapidly to perturbations to atmospherically-sourced Hg. Finally, energy pathways (source C, N and diets) are important for accurately interpret Hg source pathways and provides corroborating results to go along with the Hg isotope results. These tracers allow us to expand our understanding of bioaccumulative Hg pathways to biota. Together, multi-isotope tracing allows us for differentiation between changing Hg-source portfolios in biota and shifting diets in fish, information highly important to resource managers. |
