Tracing sources of nitrate in snowmelt runoff using a high-resolution multi-isotope technique

Abstract

To trace sources of nitrate in snowmelt runoff, stream water NO₃^- concentrations and isotopes were studied during the spring snowmelt at the Sleepers River Research Watershed, USA. We employed the denitrifier method for dual isotopic measurements for NO₃^- that requires a small water volume. During the earliest phase of lowest runoff and highest NO₃^- concentration, d18O of NO₃^- indicated higher contribution of the atmospherically derived NO₃^-. The nitrate source shifted toward deeper groundwater at the end of melt. The dual-isotope NO₃^- approach and high temporal resolution data permit the detailed evaluation of NO₃^- source changes through important hydrologic events such as snowmelt.