Upper Midwest Environmental Sciences Center
2001 Results in La Grange Pool of the Illinois River
Sampling Efforts
Stratified random sampling (SRS) for La Grange Pool began June 9 and ended August 17, 2001. Of the 430 sites targeted for sampling, 414 sites were sampled (Figure 11). Sixteen sites were not accessible and were not sampled.
Submersed Aquatic Vegetation
The status of submersed aquatic vegetation (SAV) in La Grange Pool again varied highly between contiguous strata of the river proper and nonconnected, isolated floodplain lakes[1] as it did in 2000. River stage near Havana was at or above flood stage through most of June, setting the stage for a bad year for SAV. Contiguous and isolated backwaters, main channel borders, and side channels had 0% coverage of SAV recorded during SRS (Table 7; Figure 12). Several medium-sized beds of coontail were observed while conducting an informal survey, but no sites fell within an SRS area. While small beds of sago and horned pondweeds can be found in a given season along main and side channel borders and contiguous backwaters of the lower third of the reach, SAV was absent in these areas in 2001. Isolated floodplain lake SAV was quite different. Although the mainstem river does not affect isolated floodplain lakes, such as the Banner Marsh complex and Spring Lake, these areas play an important role in the Illinois River system. While at present, the river proper supports little SAV, isolated floodplain lake SAV was present in 77 % of the samples in these two areas. Isolated floodplain lakes provided most, if not all, SAV available to migrating waterfowl within La Grange Pool in 2001.
Isolated floodplain lakes harbored the only SAV recorded in the entire reach. A total of 12 species were recorded in this stratum. Eurasian watermilfoil had the highest frequency found in a total of 61% of the sites with northern watermilfoil having the second highest frequency of occurrence (44%), and coontail being third (35%). All other species of SAV recorded were not significantly more abundant than another, ranging from 2% to 5% frequency of occurrence.
Rooted Floating-Leaf Vegetation
American lotus and white waterlily were the two rooted floating-leaf species recorded in La Grange Pool. American lotus was recorded in both contiguous backwaters and isolated floodplain lakes while white waterlily was found only in isolated floodplain lakes. As would be expected, isolated floodplain lakes had the highest percent cover of rooted floating-leaf vegetation (12%). American lotus only covered 1% of the contiguous backwaters.
[1] Lakes that are not influenced by the Illinois River.
Content manager: Danelle Larson
Page Last Modified: April 17, 2018