10.2190/Q5PY-UDCY-65RY-U4L1 Q5PYUDCY65RYU4L1 3 Nonpoint Water Quality Contributions from Land Use 127 136 20020509 20020509 20020509 20020509 Q5PYUDCY65RYU4L1.pdf http://baywood.metapress.com/link.asp?target=contribution&id=Q5PYUDCY65RYU4L1 2 Donovan C. Wilkin Randall W. Jackson College of Agriculture, University of Arizona, Tucson, Tucson, Arizona 85721 Department of Geography, University of Illinois, Urbana Stream loads of total phosphorus and nitrate-nitrogen were studied as a function of land use in a midwestern watershed of 5,853 square kilometers by means of ordinary least squares (OLS) regression analysis. The purpose was to test the general hypothesis that the variance in chemical water quality from undefined sources is a function of land use within the watershed, and to begin to study the hypothesis that land use near the stream is more important than land use far from the stream in affecting water quality from nonpoint sources. Results support both hypotheses. Further, these results suggest the importance of considering the means by which chemicals are delivered to the stream. Nitrate-nitrogen and phosphorus can apparently both be purposely intercepted, but by different means because of their different delivery systems. Nitrate-nitrogen can be intercepted by removal of fast-growing floodplain crops, and phosphorus by sediment barriers outside the floodplain. Evidence also suggests trap efficiency in reservoirs is important in improving downstream water quality. D. C. Wilkin and R. C. Flemal, Feasibility of Water Quality Improvement in Three Illinois Rivers, <i>J. Water Poll. Cont. Fed., 52</i>:2, pp. 293-298, 1980. R. A. Freeze, Role of Subsurface Flow in Generating Surface Runoff, <i>2</i>, Upstream Source Areas, <i>Water Resour. Res., 8</i>:5, pp. 1272-1283, 1972. J. D. Hewlett and W. L. Nutter, The Varying Source Area of Streamflow from Upland Basins, paper presented at Symposium on Interdisciplinary Aspects of Watershed Management, Mont. State Univ., Bozeman, Aug. 1970. S. J. Hebel, <i>The Use of Fallout Cesium-137 to Determine Patterns of Soil Movement and their Implications for Land Management and Water Quality Planning</i>, Master's Thesis, Department of Landscape Architecture, University of Illinois, 91, 1981. Wilkin, D. C. and S. J. Hebel, Erosion, Redeposition and Delivery of Sediment to Midwestern Streams, abstract published in <i>EOS, 63</i>:22, p. 527, June 1, 1982. F. E. Rhoton, N. E. Smeck, and L. P. Wilding, Preferential Clay Mineral Erosion from Watersheds in the Maumee River Basin, <i>J. Env. Qual., 8</i>:4, pp. 547-550, 1979. J. Johnston, <i>Econometric Methods</i>, McGraw-Hill, New York, 1963. J. D. Schreiber, and D. L. Rausch, Suspended Sediment-Phosphorus Relationships for the Inflow and Outflow of a Flood Detention Reservoir, <i>J. Env. Qual., 8</i>:4, pp. 510-514, 1979.