TOWARD A BETTER UNDERSTANDING OF TROPHIC DYNAMICS OF RIVER ECOSYSTEMS

Michael D. Delong

Large River Studies Center, Biology Department, Winona State University, 
Winona, MN 55987

Members of the Mississippi River Research Consortium have been considering 
the nature of trophic dynamics.  Direct studies of riverine food webs are 
relatively new to both river science and the MRRC, but the history of the 
MRRC includes numerous studies that touch on the function of river 
ecosystems.  The study of trophic dynamics dates to the second meeting of the 
MRRC, where Pahl and Varchman described the diet of three species of game 
fish.  Studies linked to trophic processes appeared sporadically in the 
intervening years, including biomass and abundance of primary producers, 
bacterial production, and secondary production of benthic invertebrates.  The 
late 1980s and early 1990s marked an effort to test the prevailing theory of 
riverine function of the time, the flood pulse concept.  This is exemplified 
by examination of the FPC during and following the 1993 flood.  Experimental 
studies added to our understanding of food webs and the interaction of a non-
native species and temporal conditions.  The development and application of 
other methodologies, such as stable isotopes, have expanded our understanding 
or riverine food webs further still.  Application of stable isotopes of 
potential food sources and consumers brought the realization that the food 
web of the Upper Mississippi, like so many other large rivers world-wide, is 
supported by autochthonous production.  Other techniques, such as fatty 
acids, have found their way into presentations at MRRC and the annual meeting 
will continue to see our understanding of riverine food webs expand as river 
scientists expand their study of the temporal and spatial dynamics of trophic 
processes.

Keywords:  history, food web, trophic, experiment, isotope, fatty acid, 
ecosystem theory