Mercury distribution in water and biota in diverse southeastern Alaskan watersheds

Information on mercury in southeastern Alaska is scarce, although lake sediment records indicate its accumulation is rising. Local sources of mercury are insignificant, but mercury-laced coal burning emissions upwind of Alaska are increasing. Our project assesses the current scale of mercury contamination in selected southeastern Alaska watersheds and examines the landscape characteristics that explain its distribution. We measured mercury concentrations in salmonids, benthic macroinvertebrates, sediments, and water in 17 watersheds (within National Park units) of various sizes, ages, and landscape cover. Our results show that the concentration of total mercury in water was highly correlated with wetland coverage and the concentration of dissolved organic carbon. Dissolved organic carbon is known to preferentially transport Hg out of wetland-rich environments and is plentiful in many southeastern Alaska streams due to the abundance of peatlands. Methylmercury was below detection in the water of all of the newer, recently deglaciated streams, but was found to be present above detection (up to 20% of the total mercury) in several of the older streams draining relatively developed wetlands. Patterns of methylmercury in fish and aquatic macroinvertebrate tissues showed preferential accumulation in biota from older, wetland-dominated watersheds over those in younger, glacier-influenced streams.