Mercury is a widespread element and persistent pollutant that enters aquatic food webs through various sources and pathways. Airborne emissions can travel long distances across the globe, depositing mercury far from human sources. Other sources occur naturally within the landscape. But how is it that remote, otherwise pristine lakes in Alaska parks contain fish with elevated levels of mercury? We study lake trout to find out.
Lake trout are a long-lived, slow-growing, top predator fish common in many southwest Alaska lakes. Because mercury bioaccumulates in long-lived species and biomagnifies up the food chain, lake trout are a good indicator of the amount of mercury present. Previously, we found that lake trout in southwest Alaska have variable and, in some cases, very elevated mercury concentrations. In this study, we analyzed lake trout tissue from two parks for stable isotopes of mercury to assess the importance of mercury from different inputs, including: from the atmosphere (via wet deposition), ocean (via salmon migration), and land (via volcanic activity). Our results suggest that:
1.
Atmospheric deposition delivers uniform levels of mercury across the study area, so deposition cannot explain the variation in lake trout mercury concentrations among lakes.
2.
Migrating salmon deliver little mercury to lake trout directly, although salmon might provide an indirect source.
3.
Active volcanoes deliver additional mercury to nearby lakes, forming a novel route of mercury exposure to aquatic food webs.
These results could help answer lingering questions about which mercury sources are bioavailable and how important volcanic emissions are to regional mercury budgets. This study is relevant and timely, as recent efforts to ban mercury use globally highlight the need for biological monitoring programs to understand the relative importance of mercury inputs.
Source: U.S. Department of the Interior, National Park Service