A retrospective analysis of suspended solids deposition in Onondaga Lake, New York: Composition, temporal patterns, and drivers

Abstract

Long-term and seasonal temporal patterns in the deposition of total (TSS), fixed (FSS) and volatile suspended solids (VSS) were documented for eutrophic Ca2+-rich Onondaga Lake, New York, for the 1980-2008 interval. Weekly collections were made from sediment traps deployed below the thermocline from April to October in the deepest area of the lake (19.5 m). Downward fluxes of TSS (DFTSS), FSS (DFFSS) and VSS (DFVSS) decreased 42, 38, and 41%, respectively, following closure of a soda ash facility in 1986 that discharged ionic waste to the lake. The DFTSS decreased 47% from 2007 to 2008, driven mostly by lower CaCO3 deposition. Sediment accumulation rates derived from dry weight deposition were estimated to decrease from 0.8 cm/yr during 1980-1986 to 0.4 cm/yr during 1987-2007 to 0.2 cm/yr in 2008. On average, DF CaCO3 accounted for 83% of DF FSS and 69% of DFTSS. The event-like character observed for DFFSS was attributed to variations in CaCO3 precipitation, probably driven by variations in temperature, pH and the availability of nucleation sites. The DFVSS decreased 56% from 2.5 g/m2 d to 1.1 g/m2 d over the 1989 to 2008 interval. Decreased phosphorus loading from a municipal wastewater treatment facility explained 67% of the interannual variations in DFVSS. Weekly variations in the DF VSS were generally correlated with chlorophyll levels in the upper waters, and maximum values were observed during major phytoplankton blooms. Seasonal minima of DFVSS and DFFSS occurred during clear water phases, associated with Daphnia grazing, which were observed annually from 1987 to 2002, and again in 2008. Changes in primary production and lake chemistry could have significant effects on the burial of contaminants and microbial metabolism in the sediments. © 2010 Copyright by the North American Lake Management Society.