Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 2002
Publication Date: July 17, 2002
Citation: TOMER, M.D., JAYNES, D.B., HATFIELD, J.L., COLE, K.J., DINNES, D.L., JAQUIS, R.J. CHARACTERIZATION OF WATER AND NITRATE FLUXES FROM A TILE-DRAINED WATERSHED. SOIL AND WATER CONSERVATION SOCIETY. 2002. V. 57(5). P. 325. Technical Abstract: In the Midwest, tile drainage is a prevalent feature that has changed the region's hydrology, and provides a ready pathway for export of leached nitrate. Effects of tile drainage on water quality are best assessed using long-term data on water and nitrate fluxes. Here we summarize tile and streamflow data from Walnut Creek in central Iowa collected between 1992 and 2000. Two tile mains draining 493 and 863 ha of land were monitored, along with the watershed outlet draining 5134 ha. Row crops occupy nearly 90% of the area. Livestock production is minimal. During nine years of monitoring, total tile flow losses were 1560 mm water and 176 kg NO3-N/ha for the smaller tile, 1710 mm water and 229 kg NO3-N/ha for the larger tile, and 1831 mm water and 168 kg NO3-N/ha for the watershed. Average NO3-N concentrations (flow-weighted) were 11.3 mg/L for the smaller tile, 13.4 mg/L for the larger tile, and 9.2 mg/L at the watershed outlet. In-stream processes, and dilution by runoff and denitrified groundwater probably caused smaller concentrations at the outlet, particularly during low-flows. Of the total mass-flux of water, a large proportion had nitrate-N concentrations greater than 10 mg/L; 59% at the smaller tile main, 73% at the larger main, and 39% at the watershed outlet. We estimated denitrification of sub-basin flows in a hypothetical wetland. Timing and large NO3-N concentrations observed for large flows may limit performance. Wetlands may not achieve water quality goals in this region without enhanced management of agricultural nitrogen.