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Journal of Environmental Quality Abstract - Surface Water Quality

Isotopic Evidence of Nitrate Sources and Denitrification in the Mississippi River, Illinois


This article in JEQ

  1. Vol. 35 No. 2, p. 495-504
    Received: Jan 14, 2005

    * Corresponding author(s): panno@isgs.uiuc.edu
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  1. Samuel V. Panno *a,
  2. Keith C. Hackleya,
  3. Walton R. Kellyb and
  4. Hue-Hwa Hwanga
  1. a Illinois State Geological Survey, Natural Resources Building, 615 E. Peabody Street, Champaign, IL 61820
    b Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495


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 δ18O and δ15N 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.

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