Impoundments used to improve wildlife habitat in Louisiana are mainly managed to produce 

 duck foods, provide water depths that make food readily available, and provide appropriate cover 

 that will attract ducks to the impoundment (Chabreck 1960; Yancey 1964; Joanen and Glasgow 

 1965; Baldwin 1968; Wicker et al. 1983). Such management is less expensive and more effective 

 where water can be exchanged as needed by using free energy such as the tides. Improvement of 

 duck habitats by using impoundments may mitigate the effects of duck habitat loss elsewhere in the 

 region. 



Types of Impoundments 



Impoundments used to improve wildlife habitat can be categorized by water depth and salinity 

 regimes into four types: permanently flooded with freshwater, manipulated freshwater, permanently 

 flooded brackish water, and manipulated brackish water (Chabreck 1960). In permanently flooded 

 freshwater impoundments, fluctuation of water depth results from natural causes. Water depth is 

 usually greatest during winter and lowest during the summer because transpiration and evaporation 

 are greatest in the summer (Chabreck 1960). Lacassine Pool, on Lacassine National Wildlife 

 Refuge in southwestern Louisiana, is a premiere example of a permanently flooded freshwater 

 impoundment (Fruge 1974). 



A manipulated freshwater impoundment has the potential for water level control and for the 

 drainage of the area. A partial drawdown stimulates growth of perennial plants, and a complete 

 drawdown promotes seed germination of annual plants. Manipulated freshwater impoundments 

 in Louisiana usually require pumping to alter the water level; in years with excessive rainfall or 

 drought, even pumping may not be efficient (Chabreck 1960). The potential to drain an area 

 allows for additional management practices such as burning, mowing, disking, or herbicide 

 application. 



The water depths in permanently flooded brackish impoundments vary considerably and are at 

 their highest level and lowest salinity during the late winter and early spring. As a result of 

 evaporation and transpiration, water depths are lowest in late summer and early fall. Water depths 

 are usually inversely proportional to salinity (Chabreck 1960). Although this impoundment type 

 is described as permanently flooded, drainage at 2- to 3-year intervals is necessary for the best 

 widgeongrass (Ruppia maritima) growth (Chabreck 1960; Morgan et al. 1975). Rainwater, tides, 

 and pumps can be used to change the water level in manipulated brackish impoundments. Salinity 

 increases can be accomplished by increasing the flow of saltwater into the impoundment during high 

 tides. Salinity is decreased in Louisiana usually by dilution with rainwater. Active water 

 management, which involves pumping, is used as a last resort if passive management, tides, and 

 rainfall are ineffective. 



Permanently Flooded Freshwater Impoundments 



Plants. Freshwater impoundments promote the growth of desirable submerged and floating- 

 leaved aquatics (Baldwin 1968). Duckweed (Lemna minor) was the dominant species in 

 permanently flooded freshwater impoundments at Rockefeller Refuge in southwest Louisiana. In 

 Lacassine Pool, the most abundant floating-leaved species were watershield (Brasenia schreberi), 

 big floatingheart (Nymphoides aquatica), and white waterlily (Nymphoides odorata), while the most 

 abundant submergents were nitella {Nitella gracilis) and bladderworts (Utricularia sp.) (Table 1). 



The establishment of watershield in flooded freshwater impoundments improves their value to 

 certain species of ducks (Chabreck 1960). The permanently flooded freshwater impoundments on 



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