METAALICUS Part II: The Fate of Mercury in Watersheds and the Recovery of Lake 658 from Elevated Mercury Deposition

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This project builds on ongoing, large-scale experiments where for six years mercury has been added to whole watersheds including upland forests, wetlands and their associated lakes. The goal is to understand trace metals cycling and to assess how newly deposited substances move through the watershed into wetlands and lakes. In this experiment, additions were originally made to the uplands, wetlands and lakes using different enriched stable isotopes, so that now the pathways of biogeochemical cycling within and among these ecosystems can be determined. Methylmercury levels in fish responded rapidly to the mercury added directly to the lake. But almost all of the mercury applied to the watershed has thus far remained there, through biogeochemical mechanisms of internal ecosystem recycling and retention that remain unknown. Researchers have a unique opportunity to determine the biogeochemical mechanisms responsible for the high degree of retention. Controls over the uptake, storage, transformation and movement of mercury among the vegetation, mineral soil, and soil and sediment organic components will be determined. The results will reveal the time scales at which trace metals are cycled in different types of ecosystems, a major unknown variable critical to modeling future dynamics. Knowing the time scale at which lakes respond to increases in deposition is especially important for the formulation of environmental policy. This interdisciplinary project will have educational impacts through support of graduate students and post-doctoral associates.