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Keywords:

  • winter hydrology;
  • rain-on-snow events;
  • nitrate;
  • soil temperature;
  • snowmelt

Abstract:  More than 85% of NO3 losses from watersheds in the northeastern United States are exported during winter months (October 1 to May 30). Interannual variability in NO3 loads to individual streams is closely related to interannual climatic variations, particularly during the winter. The objective of our study was to understand how climatic and hydrogeological factors influence NO3 dynamics in small watersheds during the winter. Physical parameters including snow depth, soil temperature, stream discharge, and water table elevation were monitored during the 2007-2008 winter in two small catchments in the Adirondack Mountains, New York State. Snowpack persisted from mid-December to mid-April, insulating soils such that only two isolated instances of soil frost were observed during the study period. NO3 export during a mid-winter rain-on-snowmelt event comprised between 8 and 16% of the total stream NO3 load for the four-month winter study period. This can be compared with the NO3 exported during the final spring melt, which comprised between 38 and 45% of the total four-month winter NO3 load. Our findings indicate that minor melt events were detectable with changes in soil temperature, streamflow, groundwater level, and snow depth. But, based on loading, these events were relatively minor contributors to winter NO3 loss. A warmer climate and fluctuating snowpack may result in more major mid-winter melt events and greater NO3 export to surface waters.