IMPACT OF ZEBRA MUSSELS ON DISSOLVED OXYGEN RESOURCES: IMPLICATIONS FOR ONONDAGA LAKE AND SENECA RIVER, NY WATER QUALITY MANAGEMENT

The Seneca River, NY is on New York State's 303(d) list of impaired water bodies for non-attainment of dissolved oxygen criteria. The 26-kilometer segment of the Seneca River from Cross Lake to the Onondaga Lake outlet is one of the State's highest priorities for total maximum daily load (TMDL) development, and a TMDL for oxygen demanding substances is scheduled for 2007. In addition to TMDL development, engineering evaluations are being performed to assess the feasibility of diverting the 85 MGD Syracuse Metropolitan Treatment Plant (Metro) effluent from Onondaga Lake, NY to the Seneca River. Both the Metro diversion decision and the TMDL have been complicated by the presence of zebra mussels (Dreissena polymorpha), an invasive species introduced to the Great Lakes system in the late 1980s that first appeared in the Seneca River sometime between 1991 and 1993, whose filtration, respiration, and excretion activities have had a profound impact on dissolved oxygen resources of the river.To capture the complexity of the system, and to guide decisions regarding the possible relocation of the Metro discharge and the TMDL, a time-variable water quality model of dissolved oxygen dynamics was developed. The model framework includes mechanistic descriptions of nutrient and phytoplankton dynamics, sediment oxygen demand, and zebra mussel growth dynamics; including respiration and filtering activity. The model has been calibrated to an extensive database, which includes ambient water quality monitoring, in-situ photosynthesis and respiration experiments, and a number of site-specific water column process studies. A diagnostic application of the calibrated model was used evaluate dissolved oxygen resources within the system. This analysis indicated that zebra mussels, both directly through metabolic activity and indirectly through depositing unconsumed particulate organic matter to the sediments, represent the dominant oxygen sink within the river.