COMPARING FISH TROPHIC DYNAMICS IN THREE FLOODPLAIN RIVERS: THE MISSISSIPPI, 
OHIO, AND MISSOURI.
 
Tiffany Schriever and Michael Delong, Large River Studies Center, Biology 
Department Winona State University, Winona MN 55987

Individual river systems offer commonalities and differences among other rivers 
with respect to geomorphology, natural and anthropogenic impacts, and food web 
dynamics. The Upper Mississippi, lower Ohio, and lower Missouri Rivers indicate 
similarities within regional constraints; however, the addition of dams, levees, 
and navigational pathways has impacted these rivers on different levels. This 
study was undertaken to define and compare the nature of higher trophic levels 
of river-floodplain ecosystems. Trophic position, which defines the location of 
higher consumers in a food web, was calculated for a range of fish species using 
stable isotope ratios of carbon and nitrogen. Fish representing piscivores, 
invertivores, omnivores, and planktivores were examined in this study.  Trophic 
position models revealed seasonal shifts as well as differences in complexity 
among the three rivers.  Trophic positions of fish in the Mississippi and Ohio 
Rivers correlated well with expected trophic level-specific locations.  Trophic 
positions of fish from the Missouri River, however, differed considerably and 
often diverged markedly from expected trophic status.  We suggest that 
similarities in trophic position of fishes in the Upper Mississippi and Ohio 
Rivers indicate that functional dynamics of these two rivers are comparable, 
despite obvious differences in overall basin morphology.  Marked differences in 
system dynamics of the Missouri, relative to the other rivers, may be attributed 
to the pronounced alteration and degradation of this formerly braided and 
hydrologically dynamic river-floodplain ecosystem.
 
Keywords: stable isotope, trophic level, food web, trophic position, fish