Upper Midwest Environmental Sciences Center
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Vegetation
- Stratified Random Sampling 2000
2000 Results in La Grange Pool of the Illinois River
Sampling Efforts
Stratified random sampling (SRS) for La Grange Pool began on June 15, 2000, and ended August 1, 2000. Of the 430 sites targeted for sampling, 425 sites were sampled (Figure 9). Five sites were not accessible and were not sampled.
Submersed Aquatic Vegetation
The status of submersed aquatic vegetation (SAV) in La Grange Pool varied highly between contiguous strata of the river proper and nonconnected, isolated floodplain lakes.* Water levels at Havana were at or above flood stage from the latter part of June through most of July. Growing conditions for SAV are less than favorable when this occurs. Contiguous and isolated backwaters, main channel borders, and secondary channels had 0% coverage of SAV recorded during SRS (Table 6; Figure 10). Several medium-sized beds of coontail were observed while conducting an informal survey, but no sites fell within an SRS area. Areas along main and secondary channel borders and contiguous backwaters of the lower third of the reach that housed SAV in previous years were void of SAV in 2000. Isolated floodplain lakes, however, housed sizable populations of SAV. The Banner Marsh complex and Spring Lake areas play an important role in the Illinois River system as they are a good seed source to the river proper and provide most of the SAV available to migrating waterfowl in the Lower Illinois River Valley. While at present, the river proper supports little SAV, isolated floodplain lake SAV was present in 80.7% of the samples in these two areas.
Isolated floodplain lakes harbored the only SAV recorded in the entire pool. A total of six species were recorded in this stratum. Eurasian and northern watermilfoil had the highest percent frequencies of occurrence among the species recorded (63.2% and 45.6%, respectively). Coontail had the third highest frequency of occurrence (28.1%).
Rooted Floating-Leaf Vegetation
American lotus, white waterlily, and floating primrose-willow were the
three rooted floating-leaf species recorded in La Grange Pool. American
lotus is the only species that was recorded in both mainstem strata and
isolated floodplain lakes. As would be expected, isolated floodplain lakes
had the highest percent cover of American lotus (8.9%), while all mainstem
strata combined was 0.7% percent cover. White waterlily and floating primrose-willow
percent cover in isolated floodplain lake stratum was 6% and 0.5%, respectively.
*Lakes that are not influenced by the Illinois River.
Content manager: Danelle Larson
Page Last Modified: April 17, 2018