TEMPORAL SHIFTS IN UPPER MISSISSIPPI RIVER FOOD WEB DYNAMICS IN RELATION TO 
HUMAN DISTURBANCES

Leah M. McIntosh1, Michael D. Delong1, James H. Thorp2, and 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


Humans rely heavily on river systems, yet the biological processes of river 
ecosystems are poorly understood. The Upper Mississippi River has been 
adversely affected by human disturbances since early settlements. The river 
serves as an important transportation route for commerce, and numerous locks 
and dams have been built to maintain navigation channels. The introduction of 
non-native species also has the potential to have altered ecosystem function. 
This study attempts to address the extent to which human activities have 
changed the food web structure of the Upper Mississippi River. Stable 
isotopes provide a way of looking at temporal changes in the trophic dynamics 
of the river. Fish muscle tissue and mollusc shell samples were collected 
from preserved museum specimens. Stable isotope ratios of carbon (?13C) and 
nitrogen (?15N) were obtained to determine food web characteristics of the 
river. Shifts in ?13C ratios suggest a change in the basal resources of the 
food chain.  There is a slight increase in ?13C ratios indicating a shift 
from pelagic to benthic food sources. Between 1900 and 1960 rates of ?15N 
increased dramatically for all samples, suggesting that the trophic positions 
may have shifted higher in the food web. These shifts correlate with the 
construction of the navigation dams and land use changes over the last 100 
yr. Stable isotope ratios of ?13C and ?15N have increased over time, and the 
changes in food web dynamics appear to correlate with anthropogenic 
disturbances to the river ecosystem.

Keywords: Upper Mississippi River, Food Web, Stable Isotopes, Historical 
Perspectives, Human Disturbances



Leah McIntosh
Large Rivers Study Center, Biology Department, Winona State University, 
Winona, MN 55987
Telephone: (507) 457-2458
Fax: (507)-457-5681
Email: LMMcinto5278@winona.edu

Poster Presentation only

Student Paper