Twain National Wildlife Refuge Batchtown unit, 1948-1951, 1954, 1958, 

 1961, 1967) (personal communication, George Payton, 1977) which adversely 

 affected the growth of wetland plants. Bellrose (unpublished) also 

 reported that much fluctuation of the pool levels occurred during the 

 growing season. It is recognized that there can be little control 

 over pool stages when levels rise above normal, but at other times, pool 

 level manipulation should take into account multiple-use decisions 

 including the effect on vegetation and animal populations (Klein et al. , 

 1975: 95). 



The Effects of Sedimentation and Turbidity . Since 1939 yearly 

 changes occurred in the production of wetland plant communities on 

 Fools 26 and 25 of the Illinois and Mississippi Rivers. These short- 

 term changes were a result of water fluctuations attributed to either 

 manipulation of pool levels by the Corps of Engineers or natural flood 

 and drought conditions (see previous section). During the late 1960's 

 the long-term effects of sedimentation and turbidity drastically af- 

 fected marsh, submerged aquatic, and floating aquatic plants. Sedi- 

 mentation and turbidity have always occurred in the Mississippi and 

 Illinois River valleys, but in recent decades sedimentation has greatly 

 increased for three major reasons: (1) a dramatic increase in row 

 crops since the 1940' s has resulted in greater rates of erosion, 

 (2) navigation dams reduced the velocity of the current, reducing 

 the river's ability to carry suspended sediment, and (3) the navigation 

 channel permitted more barge traffic which increased turbidity- by 

 disturbing bottom sediments and coupled with increased recreational 

 traffic greater bank erosion. 



Turbidity affects wetland plant communities in several ways. The 

 turbidity of water is attributable to suspended and colloidal matter, 

 the effect of which is to reduce clearness and diminish the penetration 

 of light (McKee and Wolf, 1963: 290). The greatest effect of turbidity 

 is to reduce the amount of sunlight reaching photosynthesizing plants. 

 This effect is most severe during the early growing season for both 

 submerged and emergent plants (Low and Bellrose, 1944: 17). Similar 



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