HR: 0800h
AN: H31D-1334    [Abstracts]
TI: Seasonal Variations in the Flux and Isotopic Composition of Nitrate in the Upper Illinois River
AU: * Huang, S
EM: shuang14@uic.edu
AF: University of Illinois at Chicago, Dept. of Earth & Environmental Sciences 845 West Taylor St., MC-186, Chicago, IL 60607-7059 United States
AU: Sturchio, N C
EM: sturchio@uic.edu
AF: University of Illinois at Chicago, Dept. of Earth & Environmental Sciences 845 West Taylor St., MC-186, Chicago, IL 60607-7059 United States
AU: Gonzales-Meler, M
EM: mmeler@uic.edu
AF: University of Illinois at Chicago, Dept. of Biological Sciences 845 West Taylor St., MC-066, Chicago, IL 60607-7059 United States
AU: Bohlke, J F
EM: jkbohlke@usgs.gov
AF: United States Geological Survey, Water Resources Division 431 National Center 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: Sopcak, M
EM: Michael.Sopcak@mwrdgc.dst.il.us
AF: Metropolitan Water Reclamation District of Greater Chicago, Aquatic Ecology & Water Quality Section 6001 West 39th St., Cicero, IL 60804-4112 United States
AB: The Upper Illinois River is a primary channel for transportation and receives effluent of municipal and industrial wastewater treatment facilities as well as runoff from urbanized and agricultural land within its watershed. Archived data on river discharge and nitrate concentrations are available from long-term monitoring programs of the USGS and the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC). These data show that water discharge and nitrate concentration in the Upper Illinois River vary seasonally. The isotopic composition of N and O in dissolved nitrate was measured during October 2004 and May 2005, in conjunction with the seasonal water quality monitoring program of the MWRDGC, at 49 mid-channel sampling points along a 133-mile segment of the Illinois River from Lockport to Peoria. The purpose of this study is to determine the extent to which isotopic data can be used to identify and quantify the sources and fate of nitrate in the Illinois River. In October 2004, the nitrate flux decreased from approx. 3 kg/sec at Lockport to approx. 1 kg/sec at Peoria, while the N and O isotopic compositions changed from delta-15N = +7.8, delta-18O = +0.10 at Lockport to delta-15N = +13.5, delta-18O = +5.4 at Peoria. The decrease in nitrate flux and the positively correlated increases in delta-15N and delta-18O are consistent with the interpretation that the major input of nitrate to the Upper Illinois River occurred upstream of Lockport and substantial denitrification or assimilation may have occurred downstream from Lockport. In contrast, during May 2005, the nitrate flux increased from approx. 2 kg/sec at Lockport to approx. 10 kg/sec at Peoria, while the N and O isotopic compositions changed from delta-15N = +9.7, delta-18O = +2.3 at Lockport to delta-15N = +8.9, delta-18O = +6.5 at Peoria. The increase in nitrate flux and the inverse relation between delta-15N and delta-18O are consistent with the interpretation that the major input of nitrate during May 2005 occurred downstream of Lockport and exceeded the river's capacity for denitrification.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005