Isotopic evidence of nitrate sources and denitrification in the Mississippi River, Illinois

J Environ Qual. 2006 Feb 2;35(2):495-504. doi: 10.2134/jeq2005.0012. Print 2006 Mar-Apr.

Abstract

Anthropogenic nitrate (NO3-) within the Mississippi-Atchafalaya River basin and discharge to the Gulf of Mexico has been linked to serious environmental problems. The sources of this NO3- have been estimated by others using mass balance methods; however, there is considerable uncertainty in these estimates. Part of the uncertainty is the degree of denitrification that the NO3- has undergone. The isotopic composition of NO3- in the Mississippi River adjacent to Illinois and tile drain (subsurface drain) discharge in agricultural areas of east-central Illinois was examined using N and O isotopes to help identify the major sources of NO3- and assess the degree of denitrification in the samples. The isotopic evidence suggests that most of the NO3- in the river is primarily derived from synthetic fertilizers and soil organic N, which is consistent with published estimates of N inputs to the Mississippi River. The 1:2 relationship between delta18O and delta15N also indicate that, depending on sample location and season, NO3- in the river and tile drains has undergone significant denitrification, ranging from about 0 to 55%. The majority of the denitrification appears to have occurred before discharge into the Mississippi River.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Environmental Monitoring
  • Illinois
  • Nitrates / analysis*
  • Nitrogen Isotopes
  • Oxygen Isotopes
  • Rivers*
  • Water Pollutants, Chemical / analysis*

Substances

  • Nitrates
  • Nitrogen Isotopes
  • Oxygen Isotopes
  • Water Pollutants, Chemical