Phosphorus transport pathways to streams in tile-drained agricultural watersheds

J Environ Qual. 2007 Jan 25;36(2):408-15. doi: 10.2134/jeq2006.0098. Print Mar-Apr 2007.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agriculture / methods*
  • Phosphorus / analysis*
  • Rain
  • Rivers / chemistry
  • Snow
  • Water Movements*
  • Water Pollutants, Chemical / analysis*
  • Water Supply

Substances

  • Water Pollutants, Chemical
  • Phosphorus