NUTRIENT LOADING IN THE OWASCO LAKE WATERSHED: RESULTS FROM AN AUTONOMOUS SAMPLER, R2D2

Owasco Lake, a Finger Lake of western New York, is a source of drinking water for ~44,000 residents and supports an agricultural and tourism based economy. The lake has a residence time of 1-3 years, suggesting that it may be quickly influenced by runoff from precipitation events (Halfman, 2009).

A Teledyne ISCO 6712 Portable Water Sampler (R2D2) was installed near the terminus of Dutch Hollow Brook to quantify nutrient fluxes to the lake and relative contributions of event and base-flow conditions. Dutch Hollow is the second largest tributary entering the lake (15% watershed) and drains an agriculturally rich landscape (65% land use). The sampler was programmed to automatically and autonomously collect 1-L of water every 8 hours starting in June, anticipating sufficient data to compare seasonal variability, precipitation and other events to base-flow conditions. Two In-Situ Aqua Troll 200 loggers were also installed to record stream stage, water temperature, and salinity every hour starting in March.

Water samples were collected weekly and analyzed for total phosphate (TP), dissolved phosphate (SRP), nitrates, silica, pH, conductivity, alkalinity, and total suspended solids (TSS) following standard limnological procedures. Further, the stream was sampled and measured on-site for stream discharge, pH, dissolved oxygen, conductivity and alkalinity on a bi-monthly basis, and grab samples were brought to the lab for nutrient and TSS analyses.

As expected, TP, SRP, and TSS increased and conductivity decreased from base-flow conditions to and during the largest event as recorded by stream stage data. The trends suggest a link between the stage of the river, TP, SRP, and TSS as long as the precipitation “event” generated enough runoff over the landscape. Daily precipitation data from a nearby weather station showed that pulses in stage correlate to rain events, though in a sub-linear fashion. Rainfall totals at a recording site may not be uniform across the Dutch Hollow watershed.

Continued monitoring of Dutch Hollow through the fall will hopefully provide a robust dataset of additional event and other variations, and enable the calculation of annual nutrient loads to the lake. We anticipate that the results may dictate future mitigation and remediation efforts.