Source-Pathway Separation of Multiple Contaminants during a Rainfall-Runoff Event in an Artificially Drained Agricultural Watershed
- M. D. Tomer *a,
- C. G. Wilsonb,
- T. B. Moormana,
- K. J. Colea,
- D. Heerc and
- T.M. Isenhartc
- a USDA–ARS, National Lab. for Agriculture and the Environment, 2110 University Blvd., Ames, IA 50011
b Univ. of Iowa, IIHR-Hydroscience and Engineering, Iowa City, IA 52246
c Dep. of Natural Resources Ecology and Management, Iowa State Univ., Ames, IA 50011. Mention of trade names is for information and does not constitute or imply product endorsement. Assigned to Associate Editor Robert Lerch
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. coli 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. coli loads, but not the dominant one. At the outlet, sediment, P, and E. coli were reasonably synchronous. Radionuclide activities of 7Be and 210Pb 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. coli 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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