Evaluation of effectiveness of various remediation options for Onondaga Lake

Onondaga Lake, New York, is a slightly alkaline, hypereutrophic urban lake that was subjected to industrial discharges of mercury between 1947 and 1988. Since 1991, it has been the object of an extensive study to address mercury bioaccumulation issues among other things. An extensive field data collection program was conducted in 1992 to document the temporal and spatial variability of mercury species, as well as the dynamics of mercury cycling and bioaccumulation in the lake. Mercury concentrations were measured in tributaries, surficial sediments, sediment pore water, lake water, phytoplankton, zooplankton, benthic macroinvertebrates, and fishes. A numerical model was developed based on the field data for two purposes: (1) to provide a framework for understanding the behavior of mercury in Onondaga Lake, including a mass balance analysis of sources and sinks, and (2) to permit an evaluation of remedial alternatives. The model has identified tributaries as the major source of total mercury to the lake. Sediments generally act as a sink for mercury. The most effective remedial alternative is to reduce continuing sources of mercury to the lake. Since imposition of discharge limits in 1970, fish mercury levels have decreased dramatically. Remedial options that include treatment of sediment will have littlemore » effect on the concentration of mercury in fishes. The primary site for methylmercury production is the anoxic hypolimnion. Elimination of anoxia through aeration would result in reduced methylmercury production in the water column, reduced flux of dissolved mercury from sediment, and an increased importance on the methylmercury input from a sewage treatment plant that discharges to the lake.« less