![]() ![]() ![]() Sediment accumulation rates were determined from three sediment cores using measured differences of 137Cs activity. Sediment Hg concentrations ranged from pre-mining background conditions of approximately 0.1 μg/g to a post-mining maximum of 5 μg/g. Eighteen sediment cores, 1 to 2 meters deep, collected from the 1.2 km 2 delta provide an estimate of a total mercury (Hg) inventory of 2500 ± 500 kg. Spatial trends in resident biota reflect enhanced MMHg uptake at the delta compared to other bay locations. Algal mats common to the delta’s sediment surface had MMHg concentrations ranging from 7.5 to 31.5 ng/g, and the top 1 cm of sediment directly under the mats had two times greater MMHg concentrations compared to adjacent locations without algal covering. Eleven short sediment cores (10 cm length) collected from the delta found monomethylmercury (MMHg) concentrations ranging from 0.3 to 11.4 ng/g (dry wt.), with lower concentrations occurring at the vegetated marsh and upstream channel locations. The Walker Creek intertidal delta of Tomales Bay, California is impacted by a former mercury mine within the watershed. ![]()
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