Phosphorus Transport Pathways to Streams in Tile-Drained Agricultural Watersheds

• Published in: Journal of environmental quality Vol. 36; no. 2; pp. 408 - 415
• Main Authors: Gentry, L.E, David, M.B, Royer, T.V, Mitchell, C.A, Starks, K.M
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.03.2007; American Society of Agronomy
• Subjects: agricultural runoff; agricultural watersheds; Agriculture - methods; Clean Water Act-US; Corn; Discharge; fertilizer application; Freshwater; frozen soils; Load; overland flow; particulates; phosphorus; Phosphorus - analysis; phosphorus fertilizers; pollution load; Precipitation; Rain; Rivers - chemistry; Snow; soil erosion; Soils; streams; Studies; tile drainage; Water Movements; Water Pollutants, Chemical - analysis; water pollution; Water quality; Water Supply; Water treatment plants; Watersheds; Illinois; USA, Colorado, Fork L; USA, Illinois
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2006.0098

Agriculture is a major nonpoint source of phosphorus (P) in the Midwest, but how surface runoff and tile drainage interact to affect temporal concentrations and fluxes of both dissolved and particulate P remains unclear. Our objective was to determine the dominant form of P in streams (dissolved or particulate) and identify the mode of transport of this P from fields to streams in tile-drained agricultural watersheds. We measured dissolved reactive P (DRP) and total P (TP) concentrations and loads in stream and tile water in the upper reaches of three watersheds in east-central Illinois (Embarras River, Lake Fork of the Kaskaskia River, and Big Ditch of the Sangamon River). For all 16 water year by watershed combinations examined, annual flow-weighted mean TP concentrations were >0.1 mg L-1, and seven water year by watershed combinations exceeded 0.2 mg L-1. Concentrations of DRP and particulate P (PP) increased with stream discharge; however, particulate P was the dominant form during overland runoff events, which greatly affected annual TP loads. Concentrations of DRP and PP in tiles increased with discharge, indicating tiles were a source of P to streams. Across watersheds, the greatest DRP concentrations (as high as 1.25 mg L-1) were associated with a precipitation event that followed widespread application of P fertilizer on frozen soils. Although eliminating this practice would reduce the potential for overland runoff of P, soil erosion and tile drainage would continue to be important transport pathways of P to streams in east-central Illinois.