Mercury accumulation in sediment cores from three Washington state lakes: evidence for local deposition from a coal-fired power plant.

Mercury accumulation rates measured in age-dated sediment cores were compared at three Washington state lakes. Offutt Lake and Lake St. Clair are located immediately downwind (18 and 28 km, respectively) of a coal-fired power plant and Lake Sammamish is located outside of the immediate area of the plant (110 km). The sites immediately downwind of the power plant were expected to receive increased mercury deposition from particulate and reactive mercury not deposited at Lake Sammamish. Mercury accumulation in cores was corrected for variable sedimentation, background, and sediment focusing to estimate the anthropogenic contribution (Hg(A,F)). Results indicated lakes immediately downwind of the power plant contained elevated Hg(A,F) levels with respect to the reference lake. Estimated fluxes to Lake Sammamish were compared to measured values from a nearby mercury wet deposition collector to gauge the efficacy of the core deconstruction techniques. Total deposition calculated through the sediment core (20.7 μg/m²/year) fell just outside of the upper estimate (18.9 μg/m²/year) of total deposition approximated from the wet deposition collector.