Patterns of Total Mercury Concentrations in Onondaga Lake, New York

Onondaga Lake, located in central New York, received elevated inputs of mercury from a chloralkali facility over the period 1946–1970. Despite marked reductions in mercury loading since that time, concentrations of total mercury in Onondaga Lake remain among the highest values reported in the literature, comparable to other lakes with point sources of mercury. Concentrations of mercury varied markedly in the upper waters of Onondaga Lake during the ice-free period. A large accumulation of mercury was observed in the hypolimnion during the summer stratification. This accumulation coincided with increases in dissolved sulfide concentrations produced during the period of hypolimnetic anoxia. Chemical equilibrium calculations indicate that hypolimnetic waters of Onondaga Lake were oversaturated with respect to the solubility of mercuric sulfide, and mercury sulfide complexes dominate the speciation of aqueous mercury. The formation of strong aqueous complexes with dissolved sulfide may be an important mechanism facilitating the mobilization of mercury from pelagic sediments to the water column.