See more from this Division: Joint Sessions
See more from this Session: A Celebration of Soil Science, Solute Transport, and National-Scale Water-Quality Research: In Honor of Jacob Rubin
Abstract:
For each watershed, excess nitrogen was determined by subtracting estimates of crop uptake and volatilization from estimates of nitrogen input from atmospheric deposition, plant fixation, and fertilizer and manure applications. Surface-water discharge and concentration data were used to estimate watershed nitrogen export. End-member-mixing analysis was used to estimate the amount of nitrogen removed by streambed/in-stream reactions. Denitrification in the vadose/ground-water zones was assumed to equal excess nitrogen minus surface-water export minus streambed/in-stream removal. Nitrogen inputs ranged from a low of 124 kg N/ha (WA) to a high of 163 kg N/ha (NE). Excess nitrogen ranged from about 10% (IN) to 30% (MD) of nitrogen input. The fraction of excess exported in surface water was almost 100% in the heavily tile-drained IN watershed, and ranged from 30-50% in the other watersheds. For these watersheds, streambed/stream removal of excess nitrogen ranged from 12% (WA) to 48% (MD) and was dependent on ground-water inflow and streambed characteristics. Vadose/ground-water denitrification of excess nitrogen ranged from 12% (MD) to 44% (NE) and related to ground-water redox conditions and residence time. NAWQA/ACT results show that watershed-scale nitrogen fate is controlled by the interplay of hydrologic and geochemical conditions.
See more from this Division: Joint Sessions
See more from this Session: A Celebration of Soil Science, Solute Transport, and National-Scale Water-Quality Research: In Honor of Jacob Rubin