Science Inventory

Using Carbon, Nitrogen, and Mercury Isotope Values to Distinguish Mercury Sources to Alaskan Lake Trout

Citation:

Lepak, R., J. Ogorek, K. Bartz, S. Janssen, M. Tate, Y. Runsheng, J. Hurley, D. Young, C. Eagles-Smith, AND D. Krabbenhoft. Using Carbon, Nitrogen, and Mercury Isotope Values to Distinguish Mercury Sources to Alaskan Lake Trout. Environmental Science & Technology Letters. American Chemical Society, Washington, DC, 9(4):312-319, (2022). https://doi.org/10.1021/acs.estlett.2c00096

Impact/Purpose:

Here we evaluated the importance of oceanic salmon, atmospheric deposition and volcanism to the overall mercury burden in resident lake trout of northwest Alaska. We found that mercury delivered to these lakes was closely associated with atmospheric deposition and then volcanism. The degree of volcanic influence positively associated with the proximity of lakes to the nearby volcanoes, presumably from fumarole mercury. This is important because never has volcanic mercury been identified in biota and this caused an enhanced burden in those proximate fish. Ultimately this sets new precedent toconsider volcano proximity when thinking about sources of mercury to aquatic ecosystems.

Description:

Lake trout (Salvelinus namaycush), collected from 13 remote lakes located in southwestern Alaska, were analyzed for carbon, nitrogen, and mercury (Hg) stable isotope values to assess the importance of migrating oceanic salmon, volcanic activity, and atmospheric deposition to fish Hg burden. Methylmercury (MeHg) bioaccumulation in phytoplankton (5.0–6.9 kg L–1) was also measured to quantify the basal uptake of MeHg to these aquatic food webs. Hg isotope values in lake trout revealed that while the extent of precipitation-delivered Hg was similar across the entire study area, volcanic Hg is likely an important additional source to lake trout in proximate lakes. In contrast, migratory salmon (Oncorhynchus nerka) deliver little MeHg to lake trout directly, although indirect delivery processes via decay could exist. A high level of variability in carbon, nitrogen, and Hg isotope values indicates niche partitioning in lake trout populations within each lake and that a complex suite of ecological interactions is occurring, complicating the conceptually linear assessment of the contaminant source to the receiving organism. Without connecting energy and contaminant isotope axes, we would not have understood why lake trout from these pristine lakes have highly variable Hg burdens despite consistently low water Hg and comparable age-length dynamics.