The depths of entry of municipal wastewater into receiving lakes importantly affects associated impacts on water quality. The plunging behavior of two negatively buoyant inflows that carry municipal waste, an urban tributary and an effluent discharge, in Onondaga Lake, NY, is characterized and quantified based on an integrated program of monitoring, density calculations, and modeling. In-lake signatures of plunging from the two inflows are differentiated according to constituents in which each is enriched. Under common contemporary conditions, the summer averages of the fraction of the urban stream and effluent discharge inflows plunging to stratified depths is predicted, with a calibrated hydrodynamic model, to be approximately 0.7 and 0.35, respectively. Recent short-term increases in salinity levels from construction site dewatering caused greater plunging of the effluent discharge and interfered with normal complete fall turnover in the lake.
We tested paradigms and models that relate deposition of phytoplankton constituents to lake metabolism based on analyses of long-term sediment-trap collections (28 yr of the 1980-2010 period) from a dimictic urban lake, Onondaga Lake, New York. There were major changes in a number of important drivers of deposition, including decreases in the concentration of a divalent cation (Ca 2+ ), nutrient loading and primary production, and variations in food-web effects. The summertime downward fluxes of particulate organic carbon (DF POC ), particulate nitrogen, particulate phosphorus (P), and chlorophyll were greater than values reported in the literature at the start of the program and decreased . 70% in response to decreases in Ca 2+ and P loading. Results include (1) the positive dependence of DF POC on primary production, (2) the positive dependence of the rate of hypolimnetic oxygen depletion on DF POC , (3) the negative effect of Daphnia grazing on DF POC under eutrophic and hypereutrophic conditions, and (4) the dependence of the stoichiometry of depositing material on particle origins and nutrient status of the phytoplankton community. The relationship between the export ratio, the fraction of gross primary production lost to deposition, and primary production reported in the literature was extended based on inclusion of Onondaga Lake data, and described by a nonlinear (polynomial function) relationship.
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