FOOD WEB DYNAMICS OF LARGE FLOODPLAIN RIVERS: ASSESSMENT THROUGH STABLE ISOTOPE 
ANALYSIS
 
Kelly Slattery and Michael D. Delong
Winona State University, Large River Studies Center, Biology Department, Winona, 
MN 55987

Food web ecology has become increasingly important for addressing ecological 
questions because trophic dynamics emphasize functional aspects that may be more 
sensitive to fluctuations than structural measures.  The objective of this study 
was to use stable isotope ratios of carbon and nitrogen to build food web models 
for a quantitative comparison of trophic dynamics of the Upper Mississippi, Ohio 
and Missouri Rivers. This comparative approach may make it possible to establish 
common threads in the functioning of river-floodplain ecosystems and to assess 
the impact of human alterations to structural and functional attributes. Samples 
were collected for the following components: organic matter within the water 
column, benthic algae, terrestrial vegetation within the riparian zone, and 
invertebrate and fish consumers from representative functional feeding groups. A 
combination of trophic position models and a dual-isotope, multiple-source 
mixing model were used to establish linkages from basal sources through higher 
consumers.   Energy driving the food web of the Missouri River is dissolved 
organic matter (DOM) and terrestrial organic matter.  Ultrafine transported 
organic matter and DOM were the major food sources in the Ohio River, whereas 
DOM, fine transported organic matter, and benthic algae were the primary food 
web drivers in the Upper Mississippi.  While DOM is important in all three 
rivers, there is a clear partition in the importance of transported organic 
matter in the Ohio and Upper Mississippi, compared to the significant role of 
terrestrial organic matter in the food web of the Missouri River.  Flow of 
organic matter to higher trophic levels supports the conclusion that there are 
clear differences in the functional dynamics of the Missouri River when compared 
to the other two rivers.  While natural structural differences could be 
responsible, obvious differences in the basin characteristics of the Ohio and 
Upper Mississippi should lead to greater differences here.  We propose that 
extensive anthropogenic changes in the Missouri River are the primary causal 
mechanism for differences observed in trophic dynamics.


Keywords: stable isotopes, food webs, large floodplain river ecosystems, human 
impacts, ecosystem processes