TRACKING STABLE ISOTOPES IN GROUNDWATER, STREAM WATER, AND PRECIPITATION SAMPLES IN WESTERN NEW YORK TO UNDERSTAND THE TRANSFER OF HARMFUL NUTRIENTS TO LAKE ERIE

It is crucial for our society to understand how the hydrologic cycle operates. For instance, Western New York communities rely on Lake Erie for drinking water, and harmful algal blooms (HABs) threaten human and environmental health. Groundwater in Western New York can have high nutrient loads and may be a significant source of nutrients to Lake Erie via stream water. Stable isotopes (δ¹⁸O and δ²H) in groundwater, stream water, and precipitation, provide a means to determine if streams flowing into Lake Erie are more influenced by groundwater or surface flow. Coupled with nutrient data, stable isotope data can, in turn, tell us if a majority of nutrients in streams are from groundwater or precipitation. Stream water samples have been collected and analyzed for their δ¹⁸O and δ²H values from Ellicott Creek, a major Western New York stream, and two spring-fed streams that are tributaries of Ellicott Creek. Monthly amount-weighted precipitation δ¹⁸O displays a strong correlation with seasonality; precipitation is ¹⁸O-enriched during summer months and ¹⁸O-depleted during winter months. On the contrary, δ¹⁸O values of groundwater show minimal variation seasonally. Thus, stream water isotopes that display a seasonal trend would reflect greater input from precipitation, and stream water isotopes that show little seasonal variation would reflect greater input from groundwater. I hypothesize that the isotopic composition of streams in the Lake Erie watershed reflects the isotopic composition of groundwater more than precipitation during relatively dry periods, and during dry periods, groundwater could be an important contributor of nutrients that cause HABs in Lake Erie. However, when there is an increased surface flow of water to the streams, caused by either snowmelt or an extreme precipitation event, the isotopic composition of the stream water would reflect the isotopic composition of the inflow. Determining the δ¹⁸O and δ²H composition of groundwater, stream water, and precipitation throughout Western New York will lead to a stronger understanding of the hydrologic cycle in the Lake Erie watershed, which will enable us to better quantify and mitigate future extreme precipitation events, nutrient loading, and HABs.