NUTRIENT AND SEDIMENT LOADING IN THE OWASCO WATERSHED, NEW YORK

Lake and stream monitoring in the Owasco watershed located in rural, central New York has indicate that nonpoint source inputs modulated by precipitation events impact water quality in the lake. Owasco is 18 x 2 km x 52 m deep, with an agriculturally rich (48%) land use and a water retention time of ~2 years. As a municipal water supply for the City of Auburn and the Town of Owasco, its borderline oligotrophic-mesotrophic status and recent onset of cyanobacteria blooms make it a critical resource to preserve and protect.

At least two lake sites and many stream sites were sampled seasonally since 2005. A CTD profile, Secchi disk depth, vertical plankton tow, onsite analyses, and surface and bottom water samples were collected at each lake site for total phosphate, soluble reactive phosphate, nitrate, chlorophyll-a and total suspended solid concentrations. In addition, a YSI/Xylem WQ monitoring buoy collected temperature, salinity, dissolved oxygen, fluorescence (Total and PC-BGA) profiles every 12-hours since 2014. Stream discharge was determined and grab samples analyzed for the same parameters to locate sources in the watershed. An ISCO autosampler and HOBO stage loggers was deployed in the 2^nd largest watershed, collected daily nutrient and sediment samples since 2011. Coupled with the grab sample data from this and other tributaries, estimated annual phosphorus budgets for the watershed.

The results indicate that phosphorus is the limited nutrient in lake. Over 90% of the TSS, TP, SRP and other loads are precipitation driven. Very large rain events preceded numerous HABs vents around the lakeshore. Multiple basins and SWAT modeling indicate that agricultural LULC is the primary nonpoint source, and clearly pinpoints remediation practices. Other notable sources include wastewater facilities, septic systems, and the atmosphere. The loads and its annual variability also impacted lake WQ, as yearly, daily maximum rainfalls are proportional to mean annual lake chlorophyll and total phosphate concentrations. Phosphorus inputs exceeded outputs from 2011 through 2015, degrading WQ in the lake. Subsequently, inputs balanced or were slightly below outputs. In suggests that significantly more remediation is required to return Owasco Lake back to its more pristine past, and reduce the occurrence of HABs events in this lake.