increase with overgrazing are blackrush, rattlebox, 

 marsh elder and rattlebush, none of which is valuable 

 to cattle or waterfowl. Snipe are often found in large 

 concentrations on overgrazed marsh range during the 

 winter months (Chabreck 1968a). Grazing in summer 

 and early fall reduces seed production of annual 

 grasses such as millet, bearded sprangletop, nutgrass, 

 and fall panicum, which are favorite duck foods 

 (Chabreck 1968a). Where smartweed occurs, grazing 

 will improve the area for duck usage if the marsh 

 is flooded in the fall and winter (Neely 1968). 



4.7.9 IMPOUNDMENTS 



Many species of wildlife are dependent upon wet- 

 land areas, and each year some of this land is altered 

 by draining, filling, channelization, saltwater intru- 

 sion, and pollution. As a result, conservation interests 

 have turned more and more to active management 

 practices to maintain wildlife habitat at a high level 

 of productivity (Chabreck 1977). 



One technique that is widely used to conserve 

 and improve wildlife habitat conditions is the con- 

 struction of impoundments. In the Chenier Plain 

 impounded marsh differs enough from natural wet- 

 lands that it has been identified as a distinct habitat 

 in this study. Figure 4-25 shows the location and 

 extent of impounded marsh. It comprises large 

 areas of the Chenier, Mermentau, and Sabine basins, 

 and composes 1 7.1% of the inland area of the Chenier 

 Plain. 



Impounded marshes are enclosed with a con- 

 tinuous levee for regulating or manipulating water 

 depths. In the Chenier Plain three types of impound- 

 ments are recognized. The most common type is the 

 fixed impoundment, which provides habitat for water- 

 fowl, especially dabbHng ducks. Some of these areas 

 also provide considerable amounts of freshwater sport 

 fishing. The Sabine and Lacassine National Wildlife 

 refuges and the Rockefeller Wildlife Refuge are good 

 examples of this type of impoundment. A second 

 type of impounded wetland was originally constructed 

 for agriculture. In pioneer days, farmers built levees 

 around their fields to keep the water out. After find- 

 ing that the impoundments were too expensive to 

 maintain, the famiers abandoned them and they 

 became shallow lakes. Management of continuously 

 flooded areas for the purpose of waterfowl hunting 

 began with the utilization of these abandoned agricul- 

 tural areas (Ensminger 1963). The third type of im- 

 pounded wetland includes areas that have been leveed 

 and drained for pasture. This type is discussed in part 

 4.16, pasture habitat. 



Studies indicate that plant species diversity is 

 increased by the impoundment of wetlands (Cha- 

 breck 1960, 1962a). Large, almost pure stands of 

 saltmeadow cordgrass can be drastically reduced or 

 eliminated by continuous flooding with brackish water 

 and fresh water respectively (fig. 4-26). The im- 

 poundment and subsequent reduction of dense cord- 

 grass turf allows growing space for other species. An 

 extensive Ust of plants recorded by Adams (1956) 

 for the impounded marsh areas on Rockefeller Refuge 

 is found in appendix 6.3. 



Chabreck (1962a) reported that plants pre- 

 ferred by ducks make up 50% of the vegetation in 

 the Rockefeller Refuge impoundments and less than 

 5% of the species in adjacent unimpounded areas. 

 The greatest variety of high quaUty duck foods are 

 produced in manipulated freshwater impoundments 

 (fig. 4-26). In these impoundments, the water is 

 drained during the spring or early fall to pennit 

 drying of the soil and germination of seeds from 

 grasses and sedges. The impoundments are reflooded 

 a few weeks after seed germination. As this manage- 

 ment scheme for ducks coincides with crayfish pro- 

 duction techniques, impoundments can be managed 

 for both resources (Perry et al. 1970, Chabreck 1977). 



Studies in southwestern Louisiana have reported 

 that ducks prefer natural and impounded brackish 

 marsh areas to similar fresh marsh areas during the 

 fall season and prefer the reverse during the winter 

 months (Palmisano 1972a, Chabreck et al. 1974b). 

 This difference in habitat preference is thought to 

 be related to the availability of food plants. Although 

 138 plant species occur in the large freshwater im- 

 poundment on Lacassine National Wildhfe Refuge 

 (Fruge 1974 unpublished data), Tamisier (1976) 

 clearly demonstrated that teal and pintail used the 

 impoundment primarily as a resting area and fed 

 elsewhere. 



The white-tailed deer and the American alligator 

 also benefit from impoundments. Deer benefit not 

 only from the permanent supply of freshwater and 

 increased food supply but the levees provide the deer 

 with travel lanes and cover. In Rockefeller Refuge, 

 permanently flooded fresh water impoundments 

 attract alligators. Although still listed as a "threatened 

 species" in southwestern Louisiana, alligator numbers 

 have increased enough so that controlled alligator 

 harvests are conducted. 



A list of representative vertebrate species in- 

 habiting the impounded marsh habitat is found in 

 appendix 6.3. 



Although marsh impoundments have been widely 

 used to improve habitat conditons, there are certain 

 disadvantages to this type of management. Impound- 

 ments are costly to construct and maintain, and they 

 can only be constructed in areas where the soil will 

 support the weight of the levee. Without pumping 

 facilities, unusually wet or dry years result in poor 

 quality food production for wildlife. Impounded 

 areas interact with adjacent wetlands and open 

 water areas very httle (except for waterfowl and 

 other animal species that can actively come and 

 go). Thai is, impounded areas have no appreciable 

 function as nursery areas for aquatic organisms; 

 and since the impounded areas are rarely drained, 

 there is little export of organic production to adjacent 

 systems. Most of the organic material accumulates 

 on the bottom of the impounded marsh. Turner 

 (1966) reported that in the Sabine National Wildlife 

 Refuge the impounded marsh fioor ranged from 

 slightly below MSL to 0.6 m (2 ft) above. The im- 

 pounded marsh bottom in Lacassine National Wild- 

 life Refuge is reported to be 1.5 m (5 ft) above the 

 surrounding marshes (Laurie Shiflett unpubhshed). 



192 



