SUBMERSED VEGETATION AND WATER QUALITY IN POOL 8, UPPER MISSISSIPPI RIVER, 
DURING THE DRAWDOWN OF 2001

Heidi A. Langrehr, James R. Fischer, J. Therese Dukerschein
Wisconsin Department of Natural Resources Onalaska Field Station 
575 Lester Avenue Onalaska, WI 54650

To re-establish emergent vegetation in areas where it has been declining, Pool 8 
of the upper Mississippi River was drawn down through a cooperative, multi-
agency effort (USACE, USFWS, USGS, MNDNR, WIDNR) between July 6 and August 14, 
2001. While experimental, small-scale drawdowns had been conducted in other 
areas of the Mississippi River prior to 2001, the effect of a large-scale 
drawdown on non-targeted environmental components was still unknown. It was 
possible that the increased area of shallow water would result in unusually warm 
water, decreased clarity from wind-induced sediment re-suspension, and a 
negative response in the submersed vegetation community. Since 1998, we have 
collected submersed vegetation data from 550-670 randomly selected sites per 
year in Pool 8 following standard procedures of the Long Term Resource 
Monitoring Program (LTRMP). Preliminary analysis of the data suggests little net 
change occurred in the submersed plant community of Pool 8 from 2000 to 2001. 
Likewise, water quality data from three selected LTRMP fixed monitoring sites 
(upper-, mid-, and lower-pool) indicated that water quality conditions during 
the drawdown were consistent with trends during the past 11-14 years. Water 
temperature, dissolved oxygen, turbidity, and suspended solids were not 
unusually different from previous summers with similar weather conditions. Over 
all, the drawdown did not appear to have immediate adverse effects on submersed 
vegetation, water clarity, water temperature, or dissolved oxygen in Pool 8.

Keywords:  Submersed vegetation, water quality, drawdown, Pool 8 upper 
Mississippi River, water clarity