CHANGES IN AQUATIC VEGETATION BETWEEN 1975, 1991, AND 2002 NEAR STODDARD, WI, 
POOL 8, UPPER MISSISSIPPI RIVER SYSTEM.

Heidi A. Langrehr.
Wisconsin Department of Natural Resources, Onalaska Field Station, Onalaska, WI 
54650.

Aquatic vegetation surveys were conducted near Stoddard, WI in Pool 8, Upper 
Mississippi River System (UMRS), in 1975, 1991, and 1998 through 2002.  Percent 
frequency of aquatic vegetation detected along fixed transects decreased 
dramatically from 1975 to 1991.  By the 1998-2002 period, data from stratified 
random samples taken in the same areas as the transects suggested aquatic 
vegetation had rebounded to near 1975 levels.  In his study in 1991, Fischer 
hypothesized that increased exposure to wind fetch due to loss of small islands 
in the area, along with other factors, may have contributed to the decline in 
aquatic vegetation between 1975 and 1991.  In 1997, a habitat rehabilitation and 
enhancement project was begun in the Stoddard area of Pool 8.  This project 
provided a sheltered area that likely helped promote aquatic vegetation growth 
after 1998.

Eleven species were recorded in 1975, four species in 1991, and 14 species in 
1998-2002.  All 11 species recorded in 1975 were found in the 1998-2002 sampling 
period.  Vallisneria americana Michx. was the dominant species in 1975 and was 
co-dominant with Heteranthera dubia (Jacq.) MacM. in the 1998-2002 sampling 
period.  Myriophyllum spicatum L., an exotic species not recorded in 1975, was 
the fifth most dominant species in 1998-2002.  Overall, community structure and 
species dominance was very similar between 1975 and 1998-2002.  Between 1975 and 
2002, aquatic vegetation in the area near Stoddard, WI, Pool 8, UMRS declined 
drastically and then rebounded.

Keywords:  aquatic vegetation, Mississippi River, Pool 8, trends