Wetland Vegetation 



Wetland vegetation provides important food resources and habitat for 

 both fish and wildlife. Therefore any change in the wetland vegetation will 

 profoundly affect the entier riverine ecosystem. Aquatic, marsh, and moist soil 

 vegetation in the Mississippi and Illinois River valleys has been affected by 

 (1) fluctuating water levels and (2) sedimentation and turbidity. Although 

 most of our quantitative data are from the Mark Twain National Wildlife 

 Refuge at Calhoun and Batchtown, it is felt that these areas are indicative 

 of the changes that occurred throughout Pools 24, 25, and 26. 



The implementation of the nine-foot channel increased low water levels 

 upstream from the dams. Low water levels have generally been stabilized. 

 However, fall drawdowns, a result of pool operations, adversely affected wet- 

 land vegetation during the 1950's and 1960's. These drawdowns have been 

 curtailed since 1970. 



Effects of Fluctuating Water Levels . Most aquatic plant communities 

 are adapted to specific parameters of moisture and water levels. Fluctuating 

 water levels affect aquatic plant communities on a short-term basis. The 

 fluctuating of water levels determines, to an extent, which plant communities 

 will become dominant for a given year. However, when water levels are 

 permanently raised, such as by the nine-foot channel project, a transition 

 takes place replacing former dominant plant communities with new ones. Such 

 a situation was documented at Calhoun Point by Yeager (1949: 54-57). He 

 reported that former bottomland timber areas were converted to marsh, and ex- 

 tensive growths of submerged aquatics grew in the expanded backwater areas. 



Maximum production of submerged aquatic plants depends upon stable water 

 levels (Bellrose et al. , 1977: C-34) . Gauge readings at Grafton, Illinois 

 for 1942 indicate a substantial June flood. Extreme flood conditions severely 

 decreased submerged aquatic production in 1943, 1944, and 1945 (Yeager, 1949: 

 55). These major water level fluctuations adversely affected submerged 

 plant production at Flat and Gilbert Lakes in Pool 26, Illinois River (Tables 

 38 and 39). Refuge narrative reports for the Batchtown and Calhoun units 

 indicated that during the years when stable water levels occurred, submerged 

 aquatic plants flourished. Water levels on Pool 26 were relatively stable 

 during the growing season for most of the years between 1948 and 1968, 

 except for 1951, 1960, and 1967 when water levels fluctuated during the 



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