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Isotopic Evidence of Nitrate Sources and Denitrification in the Mississippi River, Illinois
Author(s) -
Panno Samuel V.,
Hackley Keith C.,
Kelly Walton R.,
Hwang HueHwa
Publication year - 2006
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2005.0012
Subject(s) - denitrification , environmental science , nitrate , hydrology (agriculture) , tile drainage , drainage basin , discharge , nitrogen , soil water , geology , ecology , geography , soil science , chemistry , geotechnical engineering , cartography , organic chemistry , biology
Anthropogenic nitrate (NO 3 − ) within the Mississippi–Atchafalaya River basin and discharge to the Gulf of Mexico has been linked to serious environmental problems. The sources of this NO 3 − 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 NO 3 − has undergone. The isotopic composition of NO 3 − 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 NO 3 − and assess the degree of denitrification in the samples. The isotopic evidence suggests that most of the NO 3 − 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 δ 18 O and δ 15 N also indicate that, depending on sample location and season, NO 3 − 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.