TEMPORAL TRENDS IN MERCURY ACCUMULATION IN LAKE SEDIMENTS IN SWEDEN


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Abstract

Lake sediment cores were analyzed to study the history of mercury (Hg) pollution and particularly to determine whether recent sediment concentrations have declined in response to declining atmospheric deposition of Hg. Sediment cores from 6 forest lakes distributed from southern to northern Sweden and 3 northern mountain lakes were analyzed for Hg using CVAAS. A 400 cm sediment profile from Måkevatten in southwest Sweden indicates that the onset of Hg pollution occurred in the 18th century. An indisputable increase in Hg concentrations occurred concurrent with the appearance of spheroidal carbonaceous flyash particles (SCP) derived from fossil-fuel combustion, in the mid-19th century. There is a strong correlation between Hg and SCP concentrations in the sediment cores (r=0.67 to 0.91), which suggests a strong relationship between historical Hg pollution and fossil fuel burning. In contrast to sediment cores taken in 1979, maximum Hg concentrations are now observed below the sediment surface and decline towards the sediment surface. This study confirms that reductions in atmospheric deposition of Hg over Sweden have resulted in a decreased transfer of total Hg to aquatic environments as reflected by lake sediments, and that lake sediment profiles of Hg concentrations reflect relative trends in the atmospheric deposition of Hg rather than post-depositional diagenetic processes.

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