Mercury levels in walleyes from Wisconsin lakes of different water and sediment chemistry characteristics

Abstract

Forty-three lakes throughout Wisconsin were sampled in 1985-86 to determine the water and sediment chemistry characteristics that were associated with elevated concentrations of mercury in walleyes. Mean mercury concentrations for each of three different length classes of walleyes increased as the parameters lake pH, alkalinity, calcium, conductivity, or chlorophyll-a decreased. Low values for these parameters characterized most lakes in northern Wisconsin. Mean mercury concentrations exceeded the Wisconsin health standard of 0.5 micrograms (ug) Hg/g wet weight of fish for all walleye length classes in lakes with pH values or = to 15.0 inches in lakes with pH 6.0-6.9, and for walleyes > or = 20.0 in. in all lake pH categories. Apparently the older, larger walleyes in hard water as well as soft water lakes can accumulate enough mercury to warrant concern. Sediment mercury concentrations were generally or = 7.0. Models were developed and tested to predict mercury concentrations in a 17-in. walleye for each lake. The best model derived from the studymore » and tested on an independent dataset used alkalinity and calcium as independent variables. Clearly, walleyes from soft water, poorly buffered, low pH lakes have the highest concentrations of mercury, but the reasons for these higher concentrations require further study. 67 refs., 5 figs., 27 tabs.« less