HOW CHANGING WINTERS IMPACT NITRATE EXPORT IN HEADWATER STREAMS OF THE NORTHERN FOREST

For over 50 years, watershed processes have been studied at Sleepers River Research Watershed (SRRW) in northeastern Vermont. Over this time frame, substantial climatological change has occurred in the northeastern U.S., particularly in the winter. Winters have warmed by 1.7 degrees Celsius since 1960 with concurrent increases in winter precipitation and the fraction of that precipitation falling as rain, thus making recent winters more hydrologically active than those of the past. Little is known about how these alterations in northern winter hydrologic dynamics impact biogeochemical cycles and budgets. Our objective is to study winter nitrate dynamics in the W-9 catchment in SRRW to compare dominant pathways and processes during winter thaw events to those of other seasons. We will leverage rich contextual data that has been collected during nonwinter seasons and implement a comprehensive winter monitoring program that includes in-stream nitrate sensor deployment, as well as automated and grab sampling of streamwater, soil water, snowmelt, and precipitation. Those samples will be used to conduct end member mixing analysis (EMMA) to evaluate how the source of stream water changes over the course of the winter, during high-flow events, and when compared to other times of the year, and how nitrate loading is impacted during high-flow events. Early studies have determined that EMMA is an effective tool in this watershed. These data and subsequent analyses will be used to develop a conceptual model of how ongoing changes to winter hydrology are impacting nitrate export from headwater catchments of the northern forest typical of much of New York and New England. These results will be useful for predicting ongoing and future changes to the timing and magnitude of nutrient export facilitated by changes in climate and identifying potential cascading impacts on downstream ecosystems.