INFLUENCES OF LOCK AND DAM OPERATION ON PATTERNS OF FLOODPLAIN
FOREST SPECIES COMPOSITION AND GROWTH ALONG THE UPPER MISSISSIPPI
RIVER, POOL 12. 

Michelle M. Cripps.   Environmental Sciences Program, University
of Dubuque, 2000 University Avenue, Dubuque, IA 52001.  

A great deal of attention has been focused on the influence of
the navigation lock and dam system on the Upper Mississippi River
Ecosystem.  Most of the attention has been directed at the
aquatic system, primarily the role of the hydrosystem in
increasing sedimentation in the back waters.  Relatively little
attention has been paid to effects on the adjacent floodplain
forest.  The historic and evolutionary processes are those of a
flood-pulse system.  The area is inundated for a relatively short
time period in early spring, and plant species are adapted to
this wet period, generally through some form of tolerance or
dormancy.  The modifications to the hydrosystem caused by
navigation lock and dam operation are potentially severe.  The
impoundment of water behind the dams to operate the lock system
causes alterations in the flooding regime of the forests near the
locks and dam.  As an example, the operations of the Columbia
Lock and Dam on the Ouachita River has been implicated in the
die-off of one species of oak and its replacement by another
water-tolerant form in D'Arbonne National Wildlife Refuge in
northeastern Louisiana.  This study analyzes the effects of Lock
and Dam 12 near Dubuque, Iowa, on the adjacent floodplain forest
community.  Study and control sites were established at two
sites, one behind Lock and Dam 11 and the other approximately one
mile downstream (judged to be out of the influence of the lock
and dam).  Data collection consisted of line transects, quadrats,
tree identification, core samples, soil samples, air temperature,
depth to water table, and nearest neighbor analysis.    1) Short-
term effects of lock and dam operation   a)  Changes in water
table height and soil moisture were measured and compared at the
study site just upstream of the lock and dam and the control site
below the lock (midway down pool 12) and further correlated with
pool heights obtained from the U.S. Army Corps of Engineers.   b) 
Forest age information - the relative abundance of tree ages was
compared at each site to determine the intensity of disturbance
encountered at each site.  Core samples were taken from mature
trees and growth information calculated.  Growth rates from each
site were also compared to determine long-term, sublethal effects
of altered hydrosystem characteristics.  

Keywords:  Lock and Dam operation, floodplain, composition and
growth, Mississippi River, Pool 12