Lake acidity and mercury content of fish in Darwin National Reserve, Russia.

Darwin National Reserve is a protected natural area on the north-west shore of the Rybinsk Reservoir, 350 km north of Moscow. In June 1989, six lakes in the Reserve and the reservoir were surveyed to assess lake acidity and the mercury content of perch, Perca fluviatilis. Five were seepage lakes with no permanent inlets or outlets and one was a drainage lake with both an inlet and an outlet. The seepage lakes were acidic (mean pH 4.6-4.8) and varied in colour from 20 to 200 Hazen units. The drainage lake and reservoir were alkaline (mean pH 8.0-8.1) and colour spanned a similar range. The mean mercury content of perch dorsal epaxial muscle ranged from 0.5 to 1.1 microg g(-1) wet weight in the five acidic lakes and from 0.1 to 0.2 microg g(-1) in the alkaline lakes. Fish mercury content was negatively correlated with lake pH (r=-0.93, P=0.002) if all waters were considered together, and positively correlated with apparent colour (r=0.91, P=0.03) in the seepage lakes.