THE IMPACT OF LARGE PRECIPITATION EVENTS ON NUTRIENT RUNOFF TO SENECA LAKE, NY

Seneca Lake, central New York State, is an ideal natural laboratory in which to study the potential causes and sources of nutrient runoff due to human activities because it is fed by 19+ subwatersheds that drain a variety of surface areas, land use practices and bedrock characteristics. It serves over 85,000 people with Class AA drinking water, thus it is vital to the local economy and well being of the population. The research objective was to assess the affect of high precipitation events (> 100mm/48hr) on the concentration and flux of nutrients (nitrates, phosphates, silica), ions (e.g., calcium), and total suspended solids (TSS) to Seneca Lake from an agriculturally intense sub-watershed. Water samples were collected from Wilson Creek, a subwatershed of 47 km² of which almost 80% is agricultural, over the spring and summer months of 1999-2003, and discharge was measured on site using a Marsh-McBirney Flow meter. Water samples were analyzed by a spectrophotometer for nutrient concentrations, an ion chromatograph for major ions and filtration through a 0.45um filter for TSS. Special attention was paid to a large precipitation event of 274mm which occurred from May 31 to June 2 of 2003, during which samples were collected every 2 hours facilitated by an ISCO 6712 Portable Sampler. Total dissolved solids, phosphates and silica concentrations increased during this precipitation event, while calcium and nitrates do not change. However, when flux was calculated, the flux of all parameters increased during the event. Historical weather records were then used to deduce the impact of other large precipitation events on the nutrient loading within the Seneca Lake watershed. Correlations were once again found between heavy precipitation events (> 100mm/48hr) and increased concentrations and fluxes. Such correlations suggest that isolated precipitation events such as the one of May 31-June 2, in which surface runoff is exponentially increased, are directly responsible for much of the nutrient runoff to Seneca Lake. Such findings are significant, for they reveal a connection between nutrients and their surface runoff character; thus the origin of such nutrients must be ascertained and tracked so as to ensure that nutrient loading in Seneca Lake does not become an increased hazard to the local environment.