The importance of snowmelt and spring rainfall to water and nutrient exports from macro-scale watersheds (>1000 km²) is not well established. Data collected from the Androscoggin River watershed (Maine and New Hampshire) between February 1999 and March 2002 show that the 90-day spring melt period accounted for 39-57% of total annual discharge and is likely driven both by snowpack melting and spring rainfall. While large loads of dissolved inorganic nitrogen (DIN) are delivered to the watershed from snowmelt and rain (from 1.16x 10⁶ to 1.61x 10⁶ kg N over the study years), only one third of this N load is exported from the basin during the snowmelt period (0.40x 10⁶-0.48 x 10⁶ kg N). Despite reduced residence time and temperature limitations on biological N retention, there is a poor mass balance between DIN input to the watershed and the nitrogen exported from mouth of the river. Inferences from a geochemical hydrograph separation suggests that approximately 51-63% of the water leaving the mouth of the Androscoggin river is from these 'new' water sources (rain and snowmelt) while 37-49% is from DIN depleted soil and groundwater. Mixing of water from different sources, as well as nutrient retention by dams in the upper watershed, may account for the large discrepancy between DIN inputs and exports from this watershed.
