Table 3.54. The area of Chenier Plain habiuts 

 in 1974. 



Inland area excludes the Nearshore Gulf Habitat. 



Fresh, intermediate, and brackish marsh habitats 

 show similar distribution patterns. These marshes tend 

 to run parallel with the main avenue of water exchange, 

 almost perpendicular to the coast in zones of decreas- 

 ing salinity (fig. 3-15). As one moves along the coast 

 away from tlie tidal passes, the marsh zones tend to 

 form bands which are parallel with the shoreline. Col- 

 lectively, these marsh types represent nearly one-third 

 of the total area landward of the nearshore Gulf habi- 

 tat. 



In terms of area, impounded marsh represents 

 the third largest habitat. It includes aO leveed and 

 flooded wetlands, regardless of salinity, within which 

 water level is controlled to some extent. Impounded 

 marsh tends to become increasingly fresh, since rain- 

 fall exceeds evapotranspiration. It comprises one-third 



of all marsh area and, as such, is indicative of the ef- 

 fort to manage marsh for one purpose or another. Im- 

 pounded marsh is found within all the other marsh 

 types except salt marsh. The average size of an im- 

 pounded area is rather large, almost 800 ha (1^77 a). 

 Some impoundments, however, are only a few hect- 

 ares in size but one on the Sabine National WildUfe 

 Refuge is weU over 10,000 ha (24,71 1 a). 



The inland open water habitat is the largest in 

 area other than nearshore Gulf. Typically, each basin 

 contains at least one large open lake or bay. The two 

 flanking basins, Vermilion and East Bay, contain an 

 open bay system, whereas the remaining basins contain 

 large lakes. These large water bodies, which account 

 for most of this habitat type, are relatively stable in 

 comparison to the numerous small, shallow ponds 

 scattered throughout the Chenier Plain. Many of the 

 latter are rapidly increasing in size. 



All basins except Mermentau contain beach and 

 nearshore Gulf habitats. For area statistical analyses, 

 the nearshore Gulf habitat is reported by basin al- 

 though it is truly a regional habitat and has no real 

 boundaries except for the coastline. The VermiUon 

 Basin contains a large proportion of this habitat. The 

 wide, shallow shelf in this area represents the western 

 margin of Recent Mississippi River deltas (plate 2). 



The beach habitat is typically bounded on its sea- 

 ward side by the nearshore Gulf habitat and by either 

 salt or brackish marsh on its landward side. It is a 

 highly dynamic habitat. Morphological changes usually 

 occur with seasonal frequency. Sediments comprising 

 the beach are variable throughout the Chenier Plain. 

 Beach morphodynamics was discussed in part 2 (see 

 also part 4.11). 



3.4.4 HISTORICAL CHANGES IN HABITAT 

 COMPOSITION AND DISTRIBUTION 



From the perspective of tens or even hundreds of 

 years, drainage basins in the Chenier Plain are constant 

 in area. However, habitats within these basins have 

 gained or lost area in response to natural processes or 

 to man-induced disturbances. This study focuses on 

 the changes over the last 25 years, but natural processes 

 have been at work for millennia and many culturally 

 induced changes occurred before 1952. 



Habitat changes can result from normal environ- 

 mental processes. The beach habitat, for example, can 

 be displaced seaward or landward depending on sedi- 

 ment supply and other factors. Beach displacement 

 involves the loss and gain of other habitats. For in- 

 stance, shoreline advance involves the gain of habitat 

 landward of the beach (usually marsh) at the expense 

 of the seaward habitat (nearshore Gulf). 



Many recent changes have resulted directly from 

 cultural activities. These are easily documented if the 

 change is direct and intentional. The dredging of a 

 canal through a marsh Ulustrates the direct conversion 

 of marsh to inland open water habitat and to spoil 

 (ridge habitat). However, the indirect and cumulative 

 impacts of such activities are not easily determined. 



77 



