Density, Salinity, and Entry Depths of Municipal Wastewater in an Urban Lake.

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.

Whole-lake nitrate addition for control of methylmercury in mercury-contaminated Onondaga Lake, NY.

Methylmercury (MeHg) strongly bioaccumulates in aquatic food webs resulting in exposure to humans and wildlife through consumption of fish. Production of MeHg is promoted by anaerobic conditions and the supply of inorganic Hg (Hg(2+)), sulfate (SO4(2-)), and labile organic carbon. The anaerobic sediments of stratified lakes are particularly active zones for methylation of Hg(2+) and can be an important source of MeHg to the water column during summer anoxia and fall turnover. Nitrate (NO3(-)) addition has recently been proposed as a novel approach for the control of MeHg accumulation in the hypolimnia of Hg-contaminated lakes. In 2011, a whole-lake NO3(-) addition pilot test was conducted in Hg-contaminated Onondaga Lake, NY with the objective of limiting release of MeHg from the pelagic sediments to the hypolimnion through maintenance of NO3(-)-N concentrations >1mgN/L. A liquid calcium-nitrate solution was added to the hypolimnion as a neutrally buoyant plume approximately three times per week during the summer stratification interval. Maximum hypolimnetic concentrations of MeHg and soluble reactive phosphorus (SRP) decreased 94% and 95% from 2009 levels, suggesting increased sorption to Fe and Mn oxyhydroxides in surficial sediments as the regulating mechanism. Increased MeHg concentrations in the upper waters during fall turnover, which had been a generally recurring pattern, did not occur in 2011, resulting in decreased exposure of aquatic organisms to MeHg. Over the 1992-2011 interval, the hypolimnetic NO3(-) supply explained 85% and 95% of the interannual variations in hypolimnetic accumulations of SRP and MeHg, respectively.

Retrospective analyses of inputs of municipal wastewater effluent and coupled impacts on an urban lake.

A retrospective review and analysis are presented of the evolution of treatment, point of discharge considerations, and constituent loading from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), and the coupled water quality effects on the receiving urban lake (Onondaga Lake, New York) from the early 1970s to 2010. The analysis is based on long-term monitoring of the discharge, Onondaga Lake, and a nearby river system considered as a potential alternate to receive the effluent. The Metro discharge is extraordinarily large relative to the lake's hydrologic budget, representing approximately 25% of the total inflow, greater than for any other lake in the United States. The large loads of nitrogen and phosphorus received from the facility resulted in severe water quality effects in the lake during the early portion of record, including (1) violations of standards to protect against toxic effects of ammonia and nitrite, (2) violations of the water clarity standard for swimming safety, (3) exceedances of a limit for the summer average concentration of total phosphorus in the upper waters, and (4) lakewide violations of the oxygen standard during fall turnover. The effects of Metro were compounded by effects of discharges from soda ash/chlor-alkali and pharmaceutical manufacturing facilities. The sedimentary record of the lake indicates that even greater levels of cultural eutrophication prevailed before the monitoring commenced. Dramatic improvements in the water quality of the lake were achieved in recent years by implementing advanced treatment technologies. Exceedances of receiving water limits in the lake were eliminated, with the exception of the total phosphorus limit. A zebra mussel invasion compromised the oxygen resources and assimilative capacity of the nearby river for more than 15 years. This eliminated an option, previously supported by managers, of full diversion of the Metro effluent to the river.

Factors diminishing the effectiveness of phosphorus loading from municipal effluent: critical information for TMDL analyses.

Factors that diminish the effectiveness of phosphorus inputs from a municipal wastewater treatment facility (Metro) in contributing to phosphorus levels and its availability to support algae growth in a culturally eutrophic urban lake (Onondaga Lake, NY) were characterized and quantified. These factors included the bioavailability and settling characteristics of particulate phosphorus from this effluent, the dominant form (70%) of phosphorus in this input, and the plunging of the discharge to stratified layers in the lake. Supporting studies included: (1) chemical and morphometric characterization of the phosphorus-enriched particles of this effluent, compared to particle populations of the tributaries and lake, with an individual particle analysis technique; (2) conduct of algal bioavailability assays of the particulate phosphorus of the effluent; (3) conduct of multiple size class settling velocity measurements on effluent particles; and (4) determinations of the propensity of the discharge to plunge, and documentation of plunging through three-dimensional monitoring of a tracer adjoining the outfall. All of these diminishing effects were found to be operative for the Metro effluent in Onondaga Lake and will be integrated into a forthcoming phosphorus "total maximum daily load" analysis for the lake, through appropriate representation in a supporting mechanistic water quality model. The particulate phosphorus in the effluent was associated entirely with Fe-rich particles formed in the phosphorus treatment process. These particles did not contribute to concentrations in pelagic portions of the lake, due to local deposition associated with their large size. Moreover, this particulate phosphorus was found to be nearly entirely unavailable to support algae growth. While substantial differences are to be expected for various inputs, the effective loading concept and the approaches adopted here to assess the diminishing factors are broadly applicable.

The effect of municipal wastewater effluent on nitrogen levels in Onondaga Lake, a 36-year record.

This work presents a retrospective analysis of long-term trends in loading of forms of nitrogen (N) from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), N concentrations in the receiving urban lake (Onondaga Lake, New York), and related water quality status for the period from 1972 to 2007. The history of the evolution of treatment and discharge at Metro, as it affected N loading, is reviewed and forms the basis for identification of five regimes during which unifying conditions of loading and in-lake conditions prevailed. Changes in industrial waste inputs have complicated the effects of upgrades in treatment at Metro from primary (until 1978) to advanced (starting in 2004). Current N loading from Metro is approximately 35% lower than the peak levels observed in the late 1980s to late 1990s, but the areal rate to the lake remains extremely high (approximately 97 g/m(2).y), representing approximately 75% of the overall N load. Implementation of year-round nitrification treatment has resulted in transformation of the composition of the N load from Metro from ammonia (T-NH3) to nitrate (NO3(-)) dominance. High N concentrations have prevailed in the upper waters of the lake throughout the study period with averages of total N ranging from 2.6 to 4.3 mg/L for the five regimes. Total N levels and partitioning among the forms in the lake generally have tracked Metro loading conditions for the five regimes. The effects of Metro loading on seasonal in-lake patterns are demonstrated to be modified by both hydrologic inputs from tributaries and in-lake operation of biochemical processes. Resolution of these effects is supported by application of both empirical and dynamic mass balance models. Water quality problems related to high concentrations of forms of N are documented, including (1) augmentation of dissolved oxygen depletion during fall mixing from in-lake nitrification events, enabled by high T-NH3 levels; (2) violations of ammonia toxicity limits; and (3) violations of nitrite toxicity standards. These problems were either greatly ameliorated or eliminated by Metro's most recent treatment upgrades. Prevailing conditions are considered in a management context, including (1) likelihood of exceedances of toxicity limits in the future and (2) potential role of elevated nitrate levels in preventing mobilization of methyl mercury from the lake's sediments.