Nitrate in Tile Drainage of the Semiarid Palouse Basin

J Environ Qual. 2008 Feb 11;37(2):353-61. doi: 10.2134/jeq2006.0515. Print Mar-Apr 2008.

Abstract

Topographically heterogeneous agricultural landscapes can complicate and accelerate agrochemical contamination of streams due to rapid transport of water and chemicals to poorly drained lower-landscape positions and shallow ground water. In the semiarid Palouse region, large parts of these landscapes have been tile drained to enhance crop yield. From 2000-2004 we monitored the discharge of a tile drain (TD) and a nearby profile of soil water for nitrate concentration ([NO(3)]), electrical conductivity level (EC), and water content to develop a conceptual framework describing soil nitrate occurrence and loss via subsurface pathways. Tile-drain baseflow [NO(3)] was consistently 4 mg N L(-1) and baseflow EC was 200 to 300 microS cm(-1). Each year sudden synoptic increases in TD discharge and [NO(3)] occurred in early winter following approximately 150 mm of fall precipitation, which saturated the soil and mobilized high-[NO(3)] soil water throughout the profile. The greatest TD [NO(3)] (20-30 mg N L(-1)) occurred approximately contemporaneous with greatest TD discharges. The EC decrease each year (to approximately 100 microS cm(-1)) during high discharge, a dilution effect, lagged approximately 1 mo behind the first appearance of high [NO(3)] and was consistent with advective transport of low-EC water from the shallow profile under saturated conditions. Water-budget considerations and temporal [NO(3)] patterns suggest that these processes deliver water to the TD from both lower- and upper-slope positions, the latter via lateral flow during the high-flow season. Management practices that reduce the fall reservoir of soil nitrate might be effective in reducing N loading to streams and shallow ground water in this region.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Agriculture
  • Climate
  • Drainage, Sanitary
  • Electric Conductivity
  • Environmental Monitoring
  • Fertilizers*
  • Fresh Water / analysis
  • Nitrates / analysis*
  • Soil Pollutants / analysis*
  • Washington
  • Water Movements
  • Water Pollutants, Chemical / analysis*

Substances

  • Fertilizers
  • Nitrates
  • Soil Pollutants
  • Water Pollutants, Chemical