Planktonic food-web development in large rivers: Lessons from EMAP-GRE

We used survey data from the Upper Mississippi, Missouri, and Ohio rivers collected in 2004 – 2006 through the U.S. Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP) to examine the development of planktonic food-webs in these large rivers.  Conceptual constructs for large rivers generally suggest limited development of planktonic food-webs in the main channels of these ecosystems.  For example, the River Continuum Concept describes large rivers (i.e. > 8^th order) as “semi lentic,” whereas the Flood-Pulse Concept suggested there would be little autochthonous production in the main channel of floodplain-river systems.  In contrast, our data revealed Chlorophyll-a levels in all three rivers that were comparable to eutrophic lakes.  Additionally, both the Ohio and Upper Mississippi rivers had abundant zooplankton communities dominated by rotifers.  Zooplankton abundance in the Missouri River was substantially less than the Ohio or Upper Mississippi River.  A multivariate analysis combining EMAP data with GIS land-use data for the Upper Mississippi River suggests that inshore retention zones may be critical for the development of zooplankton communities.  Our data suggests that planktonic food-webs in large rivers can be substantially more developed than previously thought.  Conceptual frameworks for large rivers should be revised to include this potential.   Further work is needed to determine the physical and biotic factors associated with the development of planktonic food-webs in these systems.