An Upwelling Event at Onondaga Lake, NY: Characterization, Impact and Recurrence *

The occurrence, features and impacts on oxygen resources of an upwelling event in culturally eutrophic Onondaga Lake, NY, are documented, and recurrence is investigated, based on data collected as part of long-term, robotic, and event monitoring programs. The upwelling event occurred on September 11, 2002, in response to a wind event of average wind speed of ∼10 m s −1 that extended over an interval of 11 hours along the main axis of the lake. Longitudinal differences in temperature ( T ) and dissolved oxygen (DO) documented for the lake's surface waters during the upwelling event were 5.7 °C and 10 mg l −1 . DO concentrations <1 mg l −1 were observed in surface waters at the windward end of the lake. Oxidation of reduced oxygen-demanding by-products of anaerobic metabolism supplied to the upper waters from stratified layers during the event contributed to a loss of DO from the lake. Review of historic lake stratification, water quality related to oxygen resources, and long-term wind data indicate upwelling events with coupled deleterious impacts on DO resources have not been rare; at least 14 such events are estimated to have occurred over the 1990–2002 interval. The documented event probably represents a worst case for oxygen impacts for this period. An underway rehabilitation program, that will reduce anthropogenic phosphorus loading and implement hypolimnetic oxygenation, may ameliorate the impacts of upwelling events on the DO resources of the lake.