The English–Wabigoon River System: V. Mercury and Selenium Bioaccumulation as a Function of Aquatic Primary Productivity

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Abstract
An experiment was carried out in four 100-m3 in situ enclosures to determine the effect of primary production rate on mercury and selenium concentrations of biota and to test the possibility of ameliorating mercury pollution problems by increasing ecosystem primary productivity. Two enclosures were controls. Primary productivity in a third enclosure was increased fourfold by addition of NaNO3 and NaH2PO4. This stimulation was not sufficient to change pH although the growth rate of fish was enhanced. In this enclosure, mercury concentrations in pearl dace (Semotilus margarita) whole body and muscle samples increased two- and five-fold, respectively, exceeding the dilution of mercury by the enhanced growth rates. In the fourth enclosure, at the highest rate of nutrient addition, primary productivity was increased ninefold, pH was elevated from about 7.9 to 9.2, and the growth rate of fish was stimulated. In this case, the elevation of pH retarded the rate of mercury bioaccumulation in comparison with the enclosure of intermediate productivity. Based on these results, stimulation of primary productivity is not recommended as a mercury ameliorating procedure. Stimulation of primary productivity resulted in a general decrease in the concentration of selenium in the aquatic food chain probably resulting from dilution of selenium by enhanced growth rates of fish and other biota.

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