Mercury biomagnification and contemporary food web dynamics in lakes Superior and Huron

Trophic structure is an integral part of understanding the flow of contaminants within an aquatic system. Persistent, bioacccumulative, and toxic substances and food web perturbations by invasive species are critical ecological issues with far-reaching consequences for the health of the Laurentian Great Lakes. The historically-different aquatic ecosystems of Lakes Superior and Huron were evaluated for mercury (Hg) biomagnification using stable carbon (δ13C) and nitrogen (δ15N) isotope ratios. The results showed that δ values vary significantly with sampling depth, particularly for the lower food web components, reflecting depth- and diet-specific patterns of δ values. The stable isotope assessment of the Lake Superior food webs was consistent with previous results, underscoring the temporal stability of this ecosystem. However, based on stable isotope data, the Lake Huron lake trout appear to be incorporating the exotic round goby in their diet, possibly compensating for the collapse of alewife populations, historically their principal food. Our results suggest that the well-documented perturbations in the Lake Huron ecosystem have likely contributed to increasing Hg concentrations in the lake trout. Similar Hg biomagnification rates were observed suggesting strong similarities in the contemporary contaminant flow in Lakes Superior and Huron.