Determinants of mercury accumulation and risk for Pacific blue mussels (Mytilus trossulus) sampled along a gradient of glacial coverage

Climate change is causing rapid glacial retreat, which may affect the concentrations of trace elements in glacial outflow entering marine environments. Mercury is a trace element of interest because it bioaccumulates and poses risks to animal and human health. Although past studies have documented elevated concentrations of mercury in glacial outflow in Alaska and other regions of the world, studies assessing the fate of glacially derived mercury are lacking. We sampled Pacific blue mussels from 10 watersheds spanning a gradient of glacial influence in two regions of coastal Alaska (Kachemak Bay and Lynn Canal). We analyzed total mercury concentrations in mussel samples and investigated the factors driving these concentrations. Our results demonstrate that total mercury concentrations are tightly correlated with glacial watershed coverage in the Kachemak Bay region, but not the Lynn Canal region where some water quality parameters were more important determinants of mussel total mercury. Glacial scouring of bedrock is an important source of particulate-bound mercury in both regions, however the homogenous bedrock geology across the Kachemak Bay study area may have allowed us to better isolate the influence of glacial coverage on mussel total mercury compared to the Lynn Canal study area, where more heterogeneous bedrock likely introduces greater variability in mercury levels among proglacial streams. The proportion of Kachemak Bay mussels with mercury concentrations above the Alaska average increased with glacial coverage, though the mussel mercury concentrations from all sites do not pose risks for human or animal consumers.