Mercury Accumulation And Biological Transfer In Onondaga Lake: Ecosystem Response To Decreases In Mercury Load And Water Quality Improvements

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering


Charles Driscoll


bioaccumulation;lake;mercury;nitrate addition

Subject Categories

Civil and Environmental Engineering | Engineering | Environmental Engineering


Onondaga Lake has been adversely impacted by large inputs of mercury (Hg) from a chlor-alkali industry, which previously operated on the west shores of the lake. This dissertation represents an analysis of long-term trends in Hg concentrations in water, zooplankton, and fish of Onondaga Lake in relation to changes in Hg load to the lake and changes in water quality associated with improvements of a local wastewater treatment plant. Onondaga Lake is a saline, eutrophic urban lake in Central New York. Historically, conditions in the lake were highly conductive for production of methyl Hg, the form of Hg that bioaccumulates in aquatic food chains and controls exposure to humans and wildlife. The lake has been characterized by high Hg concentrations in water and fish. A four year (2006-2009) monitoring program was undertaken at Onondaga Lake to obtain integrated measurements of total Hg and methyl Hg in the water column, zooplankton, and fish as well as auxiliary water column parameters. In addition, historical samples for zooplankton and fish were analyzed and compiled to obtain a 30+ year record. In this dissertation I evaluate the mechanisms driving the long-term recovery of Onondaga Lake ecosystem from the Hg contamination. Elevated spring nitrate concentrations in the water column of Onondaga Lake decreased the period for methyl Hg accumulation in the hypolimnion between six and twelve weeks. This decreased the period of methyl Hg accumulation and the mass of methyl Hg in the hypolimnion. There was a 50 and 93% decrease in the hypolimnetic accumulation of methyl Hg between 2006 and 2009. Internal physical processes in Onondaga Lake were found to supply methyl Hg to the epilimnion by transporting methyl Hg from the hypolimnion, including: (1) diffusive-based mixing; (2) wind-driven entrainment of hypolimnetic layers; and (3) lake-wide mixing in the fall. Lake-wide mixing and diffusive-based transport were the main internal sources of methyl Hg to the epilimnion. The wind-driven entrainment represented an additional, stochastic supply, which contributed approximately 9% of the total internal supply of methyl Hg in 2006. The relative contribution of the internal sources decreased in recent years and shifted the importance to the external inputs. Long-term and seasonal analysis demonstrated early summer and fall enrichments of methyl Hg in zooplankton. The early summer peak was primarily due to reproduction success, while fall increases were associated with lake-wide mixing of the water column during fall turnover. Long-term trends demonstrated that zooplankton responded to the recent decreases in methyl Hg accumulation in the hypolimnion and epilimnion. Mercury concentrations in pelagic fish of Onondaga Lake were found to vary with changes within the food chain. Introduction of a macrozooplankton species in early 1990s likely resulted in biodilution of Hg into the pelagic fish. Recent increases in Hg concentrations in fish were likely associated with the introduction of new fish species and improved fish body condition. Pelagic fish in Onondaga Lake did not respond readily to decreases in Hg load to the lake. However, Hg concentrations in fish appeared to decrease in response to recent (after 2005) water quality improvements.


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