ESTIMATION OF TILE DRAINAGE CONTRIBUTION TO STREAMFLOW AND NUTRIENT LOADS AT THE WATERSHED SCALE BASED ON CONTINOUSLY MONITORED DATA

摘要

High temporal resolution water quality and streamflow data were studied using hydrograph analysis techniques together with an end-member mixing analysis (EMMA). The study area was Otter Creek a 122 km2 watershed located in northeast Iowa, USA. Attention was placed on estimating the contribution of three end-members: groundwater, tile drainage, and quick flow to both streamflow and nitrogen loads at the watershed scale. Several combinations of possible nitrate concentrations for the end-members were tested. Results show that subsurface tile drainage is responsible for at least 50% of the watershed nitrogen load between April 15 and Nov 1, 2015.