Toxic Substances Hydrology Program
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
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.