HISTORICAL ANALYSIS OF CHANGES OF RIVERINE PROCESSES IN THE ILLINOIS RIVER 
THROUGH USE OF STABLE ISTOTOPE RATIOS	

Katelyn M. Delahanty1, Michael D. Delong1, James H. Thorp2, Jeffrey R. 
Anderson3
1Large River Studies Center, Biology Dept., Winona State University, Winona, 
MN 55987.2Kansas Biological Survey, Dept. Ecology and Evolutionary Biology, 
University of Kansas, Lawrence, KS 66407. 3Large River Studies Center, 
College of Science and Engineering, Winona State University, Winona, MN 55987

	Over the past century, large river ecosystems have gone through great 
changes in their hydrology and morphology as a result of human development 
and exploitation of resources.  The objective of this study was to observe 
changes through time in food web structure throughout the Illinois River and 
to what extent human activity has caused such changes. Stable isotope ratios 
of fish were used to examine potential changes in trophic relationships as a 
result of human disturbance over a 140-yr period.  Tissue samples were 
collected and removed from museum specimens and returned to the Large River 
Studies Center to be prepared for shipment to the North Carolina State 
University Isotopic Laboratory for determination of carbon (???C) and 
nitrogen (?15N) stable isotope ratios.  Preliminary data exhibit a 
progressive increase in both ?13C and ?15N from the late 19th century to the 
middle of the 20th century followed by a decrease in both isotopic levels 
from the 1960s to 1980s. This rise may suggest the increase in organic 
pollution, causing changes in trophic levels toward benthic algae as a result 
of human activity.  Furthermore, the decrease seen in the 1980s for both ?13C 
and ?15N may serve as an indicator of the potential to rehabilitate the 
Illinois River ecosystem since the timing of this change coincides with water 
quality and improved sanitation efforts resulting from the Clean Water Act of 
1972. 

Keywords: stable isotopes, trophic relationships, organic pollution, Illinois 
River, human development


1.) Presenting author: 	Katelyn M. Delahanty
			Large River Studies Center, Biology Dept., Winona State 
			University, Winona, MN 55987
			(507)-457-2458
			Kmdelaha0634@winona.edu
			
2.) Poster presentation format only

3.) Student