title: Isotopic evidence of nitrate sources and denitrification in the Mississippi River, Illinois.
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.
authors.affiliation: Illinois State Geological Survey, Natural Resources Building, 615 E. Peabody Street, Champaign, IL 61820, USA. panno@isgs.uiuc.edu
authors.forename: Samuel V
authors.initials: SV
authors.lastname: Panno
authors.forename: Keith C
authors.initials: KC
authors.lastname: Hackley
authors.forename: Walton R
authors.initials: WR
authors.lastname: Kelly
authors.forename: Hue-Hwa
authors.initials: HH
authors.lastname: Hwang
mesh_terms: D004784:Environmental Monitoring; D007087:Illinois; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D045483:Rivers; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014874:Water Pollutants, Chemical