Effects of variable annual hydrology on a river regulated for navigation


Theiling, C., R. Maher, and R. Sparks.  1996.  Effects of variable annual hydrology on a
river regulated for navigation:  Pool 26, Upper Mississippi River System.  Journal of
Freshwater Ecology 11(1):101-114.  Reprinted by U.S. Geological Survey,
Environmental Management Technical Center, Onalaska, Wisconsin, July 1997. 
LTRMP 97-R010. 14 pp. (NTIS #PB97-189435)


ABSTRACT

We investigated impacts of water level regulation for navigation on water quality, plant
distribution and fish communities in Pool 26 of the upper Mississippi River during an
extreme drought and following a return to typical flows.  We also compared biological
responses in three hydrologically distinct pool reaches.  The third worst drought in 53
years occurred during 1989 and resulted in dam operations that created stable water
surface elevations and low current velocities through the year.  These conditions resulted
in high water clarity that allowed development of submersed and floating-leaved aquatic
plants in channel borders and backwaters; fish communities were dominated by
centrarchids (lentic species).  The drought was followed by two years of moderately high
flow.  Higher discharge resulted in lower water clarity and higher current velocity.  When
combined with drawdowns, such conditions limited submersed aquatic plant production
and promoted mesic plant species.  Centrachid abundance declined, with the lower reach
showing severe declines (from 95% of the catch in 1989 to 155 in 1991).


KEYWORDS

Fish, hydrology, Mississippi River, navigation, plants