Susan M. O'Donnell

Limnological and Loading Information and a Phosphorus Total Maximum Daily Load (TMDL) Analysis for Onondaga Lake

ABSTRACT The phosphorus (P) total maximum daily load (TMDL) analysis and associated management plan for culturally eutrophic Onondaga Lake, NY, are critically evaluated based on available input/discharge and limnological information for the system. The evaluation is based on: (1) results from a long-term monitoring program conducted on the lake, its tributaries, and the adjoining river that receives the lakes outflow, (2) algal bioassay experiments of the bioavailability of particulate P (PP) in inputs to the lake, (3) loading rate calculations for forms of P in these inputs, (4) calculations of water densities in inflows and the lake, (5) model analyses of plunging interflows and responses to seasonal material loading, and (6) mass balance calculations for a tracer conducted around the lake outlet and the receiving river to estimate inflow to the lake from the river. Several important system-specific characteristics were found not to be accommodated in the current TMDL analysis, including: (1) a P load from the river back into the lake, (2)seasonal plunging of tributaries to depths below the productive layers of the lake, (3) incomplete and different bioavailabilities of PP in the various inputs, (4) the different settling velocities of PP from these sources, (5) false high estimates of TP loading from tributaries associated with turbidity interferences in P analyses, and(6)the implications of the high flushing rate of the lake for strong seasonality in the relative impacts of externals loads. The TMDL analysis is demonstrated to understate the present role of the dominant point source and overstate the importance of non-point sources. Recommendations are made to upgrade the TMDL analysis through an integrated program of model development, testing and application, supporting process studies and monitoring, and re-evaluation of management options.

A long-term record of epilimnetic phosphorus patterns in recovering Onondaga Lake, New York

A retrospective analysis for a 23 year (1987-2009) record of spectrophotometically determined forms of phosphorus (P) is presented for the epilimnion of Onondaga Lake, New York, a period over which it was transformed from severely culturally eutrophic to mesotrophic through reductions in point source inputs. Patterns of five forms of P were evaluated, total P (TP e ), total dissolved P (TDP e ), soluble reactive P (SRP e ), particulate P (PP e = TP e -TDP e ) and dissolved organic P (DOP e = TDP e - SRP e ) based on weekly observations from multiple epilimnetic depths for the April (spring turnover) - October (fall turnover) interval of each year. A 10-fold reduction in the effluent concentration of the dominant source (TP Metro ), made in several steps, caused dramatic decreases in summer average epilimnetic P concentrations, 6.8-fold for TP e , 4.8-fold for PP e , 14.9-fold for TDP e , 8.4-fold for DOP e and 70-fold for SRP e , as well as improvements in common metrics of trophic state. Long-term patterns of summer average concentrations of each of these forms tracked the progression of TP Metro at an annual time step. Both short- and long-term patterns of in-lake concentrations, particularly for SRP e support the position that the lake remained often nutrient-saturated through much of the record, but shifted to distinctly P limited in response to the most recent (2005) reduction in TP Metro· The diagnostic value of monitoring the dynamics of these forms of P at multiple time steps to track lake metabolism and features of the P cycle is demonstrated, including uptake of dissolved forms, effects of Daphnia metabolism, dynamics of phytoplankton uptake, and long-term responses to reductions in external loading. Evidence is presented that a noteworthy fraction of the PP e pool is associated with non-phytoplankton particulates.

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 Metros 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 lakes sediments.

Insights for the structure of a reservoir turbidity model from monitoring and process studies

Abstract An array of in situ and laboratory measurements were made and in situ settling velocity experiments were conducted to support identification of model structure features necessary to simulate transient turbidity impacts in Schoharie Reservoir, NY, from runoff events. The program included: (1) extended deployments of recording instruments measuring temperature (T) and specific conductivity (SC) in the primary tributary and the reservoir surface waters; (2) automatic sampling of the tributary during runoff events for laboratory turbidity (Tn) measurements; (3) collection of vertically detailed profiles of T, SC, and the beam attenuation coefficient at 660 nm (c660; a surrogate of Tn) at multiple sites along the longitudinal and lateral axes of the reservoir with rapid profiling instrumentation; (4) chemical and morphometric characterizations of individual particles from the tributary and reservoir during dry weather conditions and for a runoff event with scanning electron microscopy coupled with automated image analysis and X-ray microanalysis (SAX); and (5) in situ measurements of settling velocity (SV) as a function of particle size with a LISST-ST®. A strong positive relationship between Tn, associated primarily with clay minerals, and tributary flow (Q), and a negative relationship between SC and Q, were reported. The entry of the primary tributary as a plunging turbid density current because of its lower T, and associated spatial and temporal patterns in c660 and SC imparted in the reservoir, were documented for two runoff events. SC was identified as a viable tracer of the movement of density currents in the reservoir, and the internal contribution of resuspension to c660 levels was depicted. The results of SAX analyses demonstrated a substantial fraction (i.e., 30–40%) of the Tn that enters the reservoir from the primary tributary was associated with particles >9.1 μm in diameter that do not contribute to Tn levels in the lacustrine portions of the reservoir. Higher SV values were observed for larger particles, but were much lower than Stokes Law conditions, suggesting that they existed as aggregates. The monitoring and SV experiment results were considered within the context of the structural needs of turbidity models, for two levels of complexity, to simulate the transient impacts of runoff events on the reservoir. A two- or three-dimensional transport submodel will be necessary to represent spatial patterns, and a kinetics submodel will need to represent (either implicitly or explicitly) size dependent settling, particle coagulation, and sediment resus-pension.

Changes in the long-term supply of mercury species to the upper mixed waters of a recovering lake.

We quantified internal processes that supply methylmercury from hypolimnetic reducing zones to the upper waters of a Hg-contaminated lake, Onondaga Lake, NY, USA. Diffusive transport continuously supplied methylmercury to the epilimnion under summer stratification, while fall mixing resulted in a pulsed release of methylmercury to the upper mixed waters. These processes were the main internal sources of methylmercury to the epilimnion, and together almost equaled the total external supply. The wind-driven entrainment represented an additional stochastic internal supply of methylmercury of approximately 9% in 2006. Considering more than 15 years of data, we estimate 1.8 wind-driven events occur per year. The mass of methylmercury inputs to the epilimnion exceeded the measured increase, suggesting that loss processes are important in regulating methylmercury accumulation. The relative contribution of internal sources of methylmercury to the epilimnion has decreased in recent years, shifting the importance to the external inputs.

Management Options Supporting a Dual Discharge Strategy for a Major Municipal Wastewater Effluent

The Metropolitan Syracuse Wastewater Treatment Plant (METRO) discharges ~80 MGD of treated effluent to the waters of Onondaga Lake, the outflow of which is received by the Seneca River. Trophic conditions in the lake are severely degraded by this input. A dual discharge strategy has been proposed under which the effluent would be diverted to the river. This, together with companion management actions, would serve to restore water quality conditions in the lake. Periodically (i.e. under certain low flow conditions), it would be necessary to return some of the diverted effluent to the lake in order to avoid violation of the river dissolved oxygen standard. Return of the effluent to the lake has the potential to increase phosphorus concentrations above the guidance value established to protect water quality there. A modeling analysis of the dual discharge strategy will be conducted, over a range of river flow conditions, to establish the frequency and magnitude of violations of the lake phosphorus guidance value. This requires specification of a suite of companion management options which would contribute assimilative capacity. These include actions focusing on the lake (e.g. P removal at METRO, reducing sediment P release through hypolimnetic oxygenation, reductions in nonpoint P contributions, and discharge of the METRO effluent to the lake’s hypolimnion) as well as on the river (e.g. elimination of density stratification in the river, oxygenation of the METRO effluent, and attention to levels of CBOD/NBOD removal at METRO). Here we describe those companion options, examine their potential for contributing assimilative capacity, and establish a base management scenario to support further analysis.

Density, Salinity, and Entry Depths of Municipal.

  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.