INVESTIGATIONS OF MERCURY DISTRIBUTION AND CYCLING IN WATERSHEDS OF SOUTHEAST ALASKA

Mercury, a widespread, naturally occurring heavy metal, is emitted by coal burning and other industrial activities and is a potent neurotoxin in its methylated form. Alaska, like many high latitude areas, is exposed to long range, atmospherically derived contaminants such as mercury, but information on this contaminant in southeast Alaska is scarce. While Hg emissions in most of the USA have decreased in recent decades due to pollution control measures, deposition to Alaska appears to be rising, possibly due to sourcing from growing releases in Asia. This presentation will provide an overview of several discrete studies conducted in southeast Alaska over the past few years to assess the scale and distribution of inorganic and methylmercury in multiple regional watersheds with a variety of landcover types that include glaciers, forests, and wetlands. Explorations of both the spatial distribution and temporal variations in inorganic and methyl mercury concentrations in freshwater media such as water, suspended particulates, bed sediments, and resident biota will be provided. Overall, our findings show that watershed landcover in this region plays a critical role in controlling methylation and the biological uptake of mercury as well as its transport to downstream nearshore ecosystems. Results to date strongly suggest that peatlands, which are a ubiquitous feature of the landscape in southeast Alaska, are particularly important for facilitating methylmercury production but that fluxes of inorganic mercury are greater in glacial streams. Temporal studies show increased mobilization and transport of mercury during high-flow events. Finally, streams with relatively high returns of spawning salmon indicate additional loading of marine-derived mercury to their watersheds.