EXPERIMENTAL EVALUATION OF MERCURY RELEASE FROM FLOODED VEGETATION AND SOILS

Significant increases in Hg concentrations have been noted in fish caught in newly-created hydroelectric reservoirs in various parts of northern Canada. It has been hypothesized that a significant contributing factor to these increased levels may be the release to the water column of Hg from flooded vegetation and soils and subsequent methylation by bacteria whose growth has been stimulated by the simulatneous release of organic matter and nutrients. A series of experiments have been carried out on a micro-scale to quantify the release over time of Hg and nutrients by various types of vegetation and soil, and to quantify methylation of the released Hg. Soil, vegetation, and water samples were collected in an undisturbed area adjacent to one of the reservoirs in northern Quebec. The vegetation and soil samples were immersed in the water in closed containers, and water samples were withdrawn periodically to permit measurements of total and methyl Hg as well as various nutrients. Dissolved O2 and pH were also routinely monitored. Additional experiments were made to examine effects of pH, temperature, and anoxia on rates of release and methylation. The results are being incorporated into an existing computer model of decomposition of flooded vegetation and soil to have better estimates of coefficients in the model to permit environmental impact predictions.