RESUMO
We conducted field studies of lakes in Darwin National Reserve in 1989, and in Karelia in 1991. Darwin National Reserve is 300km north of Moscow at the west end of Rybinsk Reservoir. The terrain is generally fiat and consists of thick sandy till covered with hardwood forest. Karelia is noth of St. Petersburg and consists of hilly terrain underlain with Precambrian bedrock. In each case, remote lakes were visited and sampled for water and fish, primarily perch Perca fluviatilis. Water samples were analyzed for pH, color, specific conductance, and major cations and anions. Fish were weigbed and measuzed, and dorsal muscle tissue was collected and analyzed for mercury. In both locations acidic lakes (acidneutralizing capacity <0) were common. Acidic Iakes were both clear and colored and the dominant anion in both types was sulfate, indicating that the Iakes were acidic because of atmospheric deposition of strong acids and not because of organic acids. Mercury content of fish ranged from 0.06 to 3.04 ug/g wet weight and was highest in acidic and in colored lakes. Fish from high-pH lakes were low in mercury regardless of lake color. Mercury content in fish from low-pH Iakes varied widely and was highest in fish from coloted, seepage lakes. Regressions including lake pH and color, separated by drainage type, explained about 70% of the variance in fish mercury seems to enter the lakes by atmospheric deposition , as there are no local sources.Organic acids are believed to increse mercury bioavailability in lakes by transporting mercury from terrestrial regions and pos sibly contributing to methylation. Also, mercuy methylation is probably enhanced in acidic lakes, incivasing bioavailability.