Factors that influence mercury concentrations in lake trout

Jake Ogorek, USGS biologist, collects water for mercury analysis in Kijik Lake, one of eight lakes in Lake Clark National Park and Preserve that was sampled for this study.

Mercury (Hg) is a persistent pollutant, harmful to fish, wildlife, and humans in its organic methylated form — methylmercury (MeHg). The risk of contamination is driven by factors that control Hg sources, cycles, and movements in food webs. At remote locations, with infrequent access and limited data, understanding the relative importance of these factors can be tricky.

This study assessed Hg concentrations in a top predator fish species, lake trout (Salvelinus namaycush), collected from 14 lakes in 2 parks in southwest Alaska. Our study also examined factors associated with the variation in fish Hg concentrations, both within and among lakes, using statistical models.

We found that total Hg concentrations in lake trout spanned a thirty-fold range (101–3,046 ng/g dry weight), with median values at 7 lakes exceeding Alaska's human consumption threshold. Model results showed that fish age and, to a lesser extent, body condition best explained variation in Hg concentration among fish within a lake, with Hg elevated in older, thinner lake trout. Other factors, including plankton MeHg content, fish species richness, proximity to volcanoes, and glacier loss best explained variation in fish Hg concentration among lakes. MeHg concentrations in plankton were higher in lakes with a greater density of nearby volcanoes, and lower in lakes with a greater loss of basin glacier cover. Plankton MeHg concentrations were strongly related to lake trout Hg concentrations, reinforcing the importance of bottom-up transfer of Hg through the food webs in these lakes.

Highlights

• Hg concentrations in lake trout vary widely within and across 14 remote Alaska lakes.
• In half of the lakes, median concentrations exceed state health criteria.
• Age and body condition control variation in Hg among fish within a lake.
• Plankton methyl Hg and volcano proximity control variation in fish Hg among lakes.

Graphical abstract, Environmental Pollution

Understanding drivers of mercury in lake trout (Salvelinus namaycush), a top-predator fish in southwest Alaska's parklands

Abstract

Mercury (Hg) is a widespread element and persistent pollutant, harmful to fish, wildlife, and humans in its organic, methylated form. The risk of Hg contamination is driven by factors that regulate Hg loading, methylation, bioaccumulation, and biomagnification. In remote locations, with infrequent access and limited data, understanding the relative importance of these factors can pose a challenge. Here, we assessed Hg concentrations in an apex predator fish species, lake trout (Salvelinus namaycush), collected from 14 lakes spanning two National Parks in southwest Alaska, U.S.A. We then examined factors associated with the variation in fish Hg concentrations using a Bayesian hierarchical model. We found that total Hg concentrations in water were consistently low among lakes (0.11–0.50 ng L⁻¹). Conversely, total Hg concentrations in lake trout spanned a thirty-fold range (101–3046 ng g⁻¹ dry weight), with median values at 7 lakes exceeding Alaska's human consumption threshold. Model results showed that fish age and, to a lesser extent, body condition best explained variation in Hg concentration among fish within a lake, with Hg elevated in older, thinner lake trout. Other factors, including plankton methyl Hg content, fish species richness, volcano proximity, and glacier loss, best explained variation in lake trout Hg concentration among lakes. Collectively, these results provide evidence that multiple, hierarchically nested factors control fish Hg levels in these lakes.

Bartz, K. K., M. P. Hannam, T. L. Wilson, R. F. Lepak, J. M. Ogorek, D. B. Young, C. A. Eagles-Smith, and D. P. Krabbenhoft. 2023. Understanding drivers of mercury inlake trout (Salvelinus namaycush), a top-predator fish in southwest Alaska's parklands. Environmental Pollution 330: 121678.