Table 3. Percentage of vegetative composition in permanently flooded brackish impoundments 

 and adjacent brackish marsh on Rockefeller Refuge in 1959 (data from Chabreck 1960). 



saturated but dewatered condition. In late spring or early summer, the marsh is completely drawn 

 down for 1 to 2 weeks, then reflooded to a depth of 15 to 20 cm. Throughout the remainder of 

 the growing season, water levels are gradually raised to depths of 46 to 76 cm, and water 

 circulation is maintained (Prevost 1987). This management regime provides optimum conditions 

 for production of important brackish water duck-food plants. A spring drawdown with moist soil 

 conditions allows saltmarsh bulrush (Scirpus maritima) to sprout on areas of higher elevations. 

 Moist soil minimizes acid conditions associated with prolonged drainage of brackish marshes 

 (Edelman and Van Staveren 1958; Neely 1958). Complete drawdown prior to reflooding in early 

 summer stabilizes soils and minimizes turbidity, thereby enhancing widgeongrass germination and 

 growth and helping prevent wave action from uprooting widgeongrass seedlings (Joanen and 

 Glasgow 1965). Late summer die-offs of widgeongrass (Percival et al. 1970) and destruction of 

 widgeongrass stands by filamentous algae {Cladophora sp.) (Prevost et al. 1978) generally can be 

 avoided by early summer flooding followed by vigorous water circulation and gradual elevation of 

 water levels. 



Wildlife. Manipulated brackish impoundments provide excellent dabbling duck habitat and are 

 also used by diving ducks, snow geese {Chen caerulescens), and coots. The cycle of flooding and 

 draining attracts wading birds. This habitat type is ideal for fur animals. Abundant cover, food, 

 and feeding conditions are available for both herbivores and carnivores (Chabreck 1960). 



Advantages and Disadvantages of Impoundments 



Impoundments enhance waterfowl wintering habitat. At Rockefeller Refuge, the impoundments 

 produced an abundance of food as well as provided an ideal resting area for ducks. Of the total 

 number of ducks on the refuge, about 80% used the impoundments. Aerial inventories by the 

 Louisiana Wildlife and Fisheries Commission revealed that Rockefeller Refuge wintered fewer than 

 75,000 ducks in 1951 and 1952 prior to the construction of the impoundments. In 1958-59, the 

 inventory indicated that 443,000 ducks wintered on Rockefeller Refuge (Chabreck 1960). 

 Improvement of duck habitat by impoundments may mitigate the effects of duck habitat loss 

 elsewhere in the region. Impoundments may simply redistribute ducks, causing crowding and 

 promoting disease transmission (Whitman 1976), but this has not been identified as a problem in 

 Louisiana. 



More nongame species than game species use impoundments (Epstein and Joyner 1986). 

 Strange (1987) stated that it is impossible to manage an impoundment for a certain species without 

 benefiting many other species. 



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