U.S. Geological Survey
Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B
Isotopic Tracing of Nitrogen Sources and Cycling in the Mississippi
River Basin
By Carol Kendall, William A. Battaglin, Gilbert Cabana, Cecily
C. Chang, Steven R. Silva, Stephen D. Porter, Donald A. Goolsby,
Donald H. Campbell, Richard P. Hooper, and Christopher J. Schmitt
ABSTRACT
As part of five pilot studies, several different isotopic approaches
for tracing nutrient sources, land uses, and nitrogen cycling
processes that are contributing nitrogen to the Gulf of Mexico are
being evaluated. Analysis of nitrate for both 15N and
18O enhances our ability to distinguish between
variations in 15N due to mixing of sources and
variations due to denitrification. Analysis of organic matter for
13C, 15N, and 34S provides
information on the terrestrial versus aquatic origin of the
material. The 15N of fish collected at large-river are
evaluated as integrators of local variability in nitrogen
sources. Preliminary data from these fish suggest that source
signatures are being substantially overprinted by other processes
at these sites.
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