CURRENT STATUS OF THE BENTHIC COMMUNITY OF POOL 19,
MISSISSIPPI RIVER.

Robert Kennedy, Richard V. Anderson, Melissa Morgan,
Dept. of Biological Sciences, Western Illinois
University, Macomb, IL  61455.

Benthic samples have been collected at standard sites
in Pool 19, Mississippi River for over 25 years. 
During this period benthic density and diversity has
fluctuated substantially.  During this period
sedimentation, extreme droughts and floods have also
occurred.  When evaluating the benthic data in terms of
habitat changes brought about by these extreme events
some specific relationships are apparent.  Burrowing
forms of benthic organisms occur in the channel border
habitat of most of the lower reach of Pool 19.  Dense
populations (1-10 X 104/m2) of some of these burrowing
benthic organisms, particularly fingernail clams
(Musculium) and burrowing mayflies (Hexagenia), occur
in soft sediments in association with vegetation but
not directly in vegetated habitats.  When areas of soft
substrate develop vegetation, such as during droughts
or when sedimentation decreases water depths,
populations of these benthic organisms are greatly
reduced (>100/m2).  However, if flooding  removes the
vegetation the Musculium, Hexagenia dominated benthic
community is quickly reestablished an appears to
persist until dense stands of aquatic macrophytes again
develop.  The aquatic macrophytes produce unsuitable
conditions in the substrate below the plants but
provide a good food source in adjacent benthic habitat. 
Once sedimentation rates stabilize in an impounded
reach of a navigation pool, density of fingernail clams
and burrowing mayflies may fluctuate in relation to
flooding or drought events of sufficient magnitude to
alter patterns of aquatic macrophyte development.



Robert Kennedy
Dept. Biological Sciences
1 University Circle
Western Illinois University
Macomb, IL  61455

Phone:  309-298-155
FAX: 309-298-2270
email: randerso@ccmail.wiu.edu

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