| Summary: | Arctic freshwater ecosystems are subject to profound climate-driven changes. Air temperatures are rising, leading to changes that include increased primary production and enhanced permafrost degradation. These and other climate-related effects interact to influence the accumulation of mercury in sediments and food webs of Arctic lakes. Mercury is a neurotoxin that is harmful to human and animal health, and in its methylated form, mercury can be taken up and biomagnified through food webs. The controls on mercury deposition, bioaccumulation, and biomagnification are complex and spatially variable. An area where especially little is known about spatial and temporal variability in mercury accumulation is in the food webs and sediments of lakes on the Arctic Coastal Plain of Alaska (ACP), a lake-rich region in northern Alaska. Sediment cores were collected from three thermokarst lakes on the ACP and analyzed to understand changes in, and drivers of, Hg accumulation over the past ~100 years (Chapter 2). Mercury accumulation in two of the three lakes was variable and high over the past century (mean=37.4 µg/m2/year and mean = 45.8 µg/m2/year), and largely controlled by sedimentation rate. Mercury accumulation in the third lake was lower (mean = 6.5 µg/m2/year), more temporally uniform, and was more strongly related to sediment Hg concentration than sedimentation rate. Sediment mercury concentrations were quantitatively related to measures of sediment composition and VRS-inferred chlorophyll-a, and sedimentation rates were related to various catchment characteristics. These results were compared to data from 37 previously studied Arctic and Alaskan lakes. Results from the meta-analysis indicate that lake thermokarst lakes have significantly higher and more variable Hg accumulation rates than non-thermokarst lakes, suggesting that properties of thermokarst lakes, such as thermal erosion, thaw slumping, and low hydraulic conductivity likely make these lakes prone to high and variable Hg accumulation rates. Following the ...
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