Table 1. Percentage of occurrence of floating-leaved species in Lacassine Pool, 1974 (data from 

 Fruge 1974). 



Species Percentage of occurrence 



Watershield 78.57 



American lotus 2.38 



White waterlily 45.24 



Big floatingheart 76.19 



Rockefeller Refuge were dependable duck food producers, although the food produced (other than 

 duckweed) was of low quality (Chabreck 1960). 



Wildlife. Permanently flooded freshwater impoundments receive high use by waterfowl. Gadwall 

 (Anas strepera) and American wigeon (Anas americana) feed heavily on the leafy plant materials. 

 Diving ducks such as ring necked ducks (Aythya collaris) prefer this habitat type and concentrate 

 there in large numbers. Water depths are often too deep for bottom feeding dabblers. 

 Permanently flooded impoundments are particularly valuable to ducks during prolonged droughts, 

 when most marshes are dry. Rails and gallinules use this impoundment type year round, and 

 wading birds often use this impoundment type if shallow water is available. Nutria (Myocaster 

 coypus) do very well in this habitat type; however, muskrats (Ondatra zibethicus) are limited by the 

 absence of preferred food plants. Excellent feeding conditions and abundant prey species for the 

 alligator occur in habitat provided by permanently flooded impoundments (Chabreck 1960). In 

 Lacassine Pool, 94.6% of the alligator nests were located in the impoundment, as compared to 

 5.4% on an area of equal size outside the impoundment (Carbonneau 1987). 



Manipulated Freshwater Impoundments 



Plants. The most common method of manipulating freshwater marshes includes partial or 

 complete drawdown during the growing season to promote the growth of moist soil annuals 

 (Baldwin 1956; Conrad 1966; Morgan et al. 1975). Wild millet (Echinochloa walteri) is an 

 important food of ducks in Louisiana (Chamberlain 1959; Kimble and Ensminger 1959) and was 

 the dominant species in manipulated freshwater impoundments at Rockefeller Refuge (Table 2). 



Important duck-food plants constitute 87.5% of the impoundment vegetation and 50.7% of the 

 plants in the control area. In a floating freshwater marsh impoundment in southcentral Louisiana, 

 the major species were pennywort (Hydrocotyla sp.), spikerush (Eleocharis sp.), and paspalum 

 (Paspalum sp.), while water hyacinth (Eichhomia crassipes) and spikerush were the major species 

 within the control area (Carney and Chabreck 1977). The impounded area contained 24.4% more 

 duck-food plants than the control area. Water hyacinth was drastically curtailed within the 

 impoundment and constituted only 0.5% of the vegetation in the impoundment but made up 18.8% 

 within the control area. The reduction of water hyacinth was probably related to the drier 

 conditions within the impoundment during drawdown (Carney and Chabreck 1977). The 

 manipulated freshwater impoundments on Rockefeller produced an abundance of high quality 

 food, but without absolute water level control, lean years were inevitable (Chabreck 1960). 



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