Source-Pathway Separation of Multiple Contaminants during a Rainfall-Runoff Event in an Artificially Drained Agricultural Watershed

A watershed's water quality is influenced by contaminant-transport pathways unique to each landscape Accurate information on contaminant-pathways could provide a basis for mitigation through well-targeted approaches This study determined dynamics of nitrate-N. total P, Escherichia coli, and sediment during a runoff event in Tipton Creek. Iowa The watershed, under crop and livestock production, has extensive tile drainage discharging through an alluvial valley A September 2006 storm yielded 5 9 mm of discharge during the ensuing 7 d, which was monitored at the outlet (19,850 ha), two tile-drainage outfalls (total 1856 ha), and a runoff flume (11 ha) within the sloped valley Hydrograph separations indicated 13% of tile discharge was from surface intakes Tile and outlet nitrate-N loads were similar, verifying subsurface tiles dominate nitrate delivery On a unit-area basis, tile total P and E cob loads, respectively, were about half and 30% of the outlet's, their rapid, synchronous timing showed surface intakes are an important pathway for both contaminants Flume results indicated field runoff was a significant source of total P and E. colt loads, but not the dominant one At the outlet, sediment. P. and E cob were reasonably synchronous Radionuclide activities of Be-7 and Pb-210 in suspended sediments showed sheet-and-rill erosion sourced only 22% of sediment contributions, therefore, channel sources dominated and were an important source of P and E colt. The contaminants followed unique pathways. necessitating separate mitigation strategies. To comprehensively address water quality, erosion-control and nitrogen-management practices currently encouraged could be complemented by buffering surface intakes and stabilizing stream banks