PRECIPITATION INDUCED NUTRIENT LOADING VARIABILITY BETWEEN TWO TRIBUTARIES IN THE OWASCO LAKE WATERSHED, CENTRAL NEW YORK

Past research has shown precipitation events deliver the majority of the suspended sediments (TSS) and nutrients from Dutch Hollow Brook, an agriculturally-rich watershed (65% agricultural, 39% forested land), to the phosphorus (P) limited Owasco Lake, one of the eleven Finger Lakes in New York State. In 2013, we expanded our nutrient loading investigation to include the Owasco Inlet. These tributaries drain the majority (71%) of the Owasco watershed. The Owasco Inlet is larger, is lower gradient, and drains less agricultural land than Dutch Hollow Brook, thus may be less prone to event signatures (299 km² vs. 77 km², 47% vs. 52% agricultural land).

Teledyne ISCO 6712 portable water samplers (R₂D₂) were installed near the terminus of both tributaries from 6-11-2013 through 7-9-2013. They were programed to collect 1-L of water every eight hours. The 24-bottle samplers were serviced weekly and each water sample was analyzed for total and dissolved P, TSS, dissolved silica, nitrates, alkalinity, conductivity, and pH by standard limnological methods. Stream stage was measured by a bubble logger at Dutch Hollow Brook and by a USGS stream gauge (04235299) just upstream from the Owasco Inlet site.

Both streams revealed varying amounts of nutrients and event signatures in TSS and P concentrations during the deployment. However, the magnitude and timing of the events were not consistent between the two watersheds. Variations in watershed geomorphology, land use, and rainfall may generate these differences, and precipitation variability is the focal point of this poster.

Daily rainfall data (www.CoCoRaHS.org) from stations within or near each watershed revealed that more rain (~1.7 times) fell over Dutch Hollow Brook than Owasco Inlet during the investigation, and the timing of the rain events differed as well. The rain events were consistent with the observed events in stream stage, TSS and P concentrations in each respective watershed but not between watersheds. It indicates that rainfall variability is large enough within the 523 km² Owasco watershed to influence the timing and magnitude of suspended sediment and phosphorus loading to Owasco Lake. Future watershed/nutrient loading models might elucidate the relative contributions of geomorphology, land use and precipitation.