Date of Completion

8-24-2011

Embargo Period

9-6-2011

Open Access

Open Access

Abstract

The accumulation of methyl mercury (MeHg) in lakes during summer stratification has been demonstrated to affect biotic mercury (Hg) accumulation. However, small, shallow polymictic lakes can experience short-term stratification and mixing events that are largely unstudied in their abilities to affect Hg cycling and MeHg accumulation. Short-term stratification events and changing lake characteristics impact lake biogeochemical cycles, and therefore, MeHg production and transport. A field and modeling analysis was performed on a small suburban lake located on the University of Connecticut campus to determine the impact of lake characteristics on the potential for MeHg accumulation. MeHg concentrations ranged from non-detect – 0.095 ng L-1 in daily outlet samples and non-detect – 0.104 ng L-1 for samples collected from the water column during stratified conditions during the summers of 2009 and 2010. Laboratory methylation investigations using lake sediments demonstrated a potential adjusted MeHg accumulation rate in the hypolimnion of 0.00155 ng L-1 hr-1, sufficient to produce accumulation in the lake given appropriate conditions. A modeling analysis was performed to evaluate the impact of lake condition parameters on MeHg accumulation. Stratification length did not impact MeHg accumulation; and while the input rate and demethylation rate affected the long-term steady state concentration, the key parameter for increasing hypolimnetic accumulation was increased submerged aquatic vegetation. This research indicates that small, shallow lakes have the capacity for MeHg accumulation and should be evaluated when determining MeHg transport and export in a watershed.

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