Consumers . The discussion of consumers in the fresh marsh description is 

 applicable to the delta marsh. It should be emphasized that waterfowl and 

 colonial birds rely heavily upon this ecosystem. Terrestrial animals are, of 

 course, restricted to natural levees or artificially constructed high ground. 

 The fauna may be forced to occupy a restricted area during the flooding season; 

 food and cover can be \/ery scarce during this period. 



Summary . The delta marsh is a very dynamic system, which is dependent 

 upon (and almost totally regulated by) the upland drainage. Riverine flows 

 are responsible for transporting the sediment and nutrient loads that support 

 and extend the delta. Subsidence and deposition are concomitant processes which 

 determine water depth, the main regulator of vegetation. Vegetative composition 

 is thus in a constant state of flux, adapting to or failing to adapt to the 

 natural perturbations of the deltaic cycle. The total consumer biomass that 

 can be supported by this vegetation is, in turn, highly variable. Inter- and 

 intraspecific competition become significant when vegetation favorable to wild- 

 life is scarce. 



Levees and Spoil Banks 



An ecosystems diagram for levees and spoil banks is presented in Figure 

 3-9. Ridges, levees, and spoil banks are the result of either artificial or 

 natural changes in the geomorphology of the coastal substrate. Artificial 

 levees and spoil banks are formed as a result of various coastal reclamation, 

 developmental, or operational activities and alterations, and they are becoming 

 increasingly numerous. Physical properties of the levee substrate are dictated 

 in part by the kind of original material dredged, whether sand, silt, mud, or 

 a mixture, and are therefore highly variable (Fisher et al., 1973). Newly formed 

 levees and spoil areas are unvegetated and extremely susceptible to formed ero- 

 sion and reworking. Stabilizing vegetation can modify these processes. 



Natural ridges, commonly referred to as cheniers in Louisiana and parts 

 of Texas, are geologic formations produced by interactions between the deposi- 

 tional processes of riverine systems, primarily the Mississippi River delta, 

 and the erosional mechanisms of coastal waters (Chabreck, 1972; Fisher et al., 

 1973). Chenier ridges are typically narrow, elongate, and composed of sand 

 and silt with minor amounts of shell material (Chabreck, 1972). Relief is 

 typically low, and elevation ranges from one to two m (three to six ft) above 

 mean sea level. Chenier ridges in Texas are restricted in distribution, are 

 largely grass covered, and only locally support scrub oak vegetation. Ridges 

 in Louisiana are more extensive, well defined, and char-acteristically support 

 dense live oak stands (O'Neil, 1949; Fisher et al., 1973). Intervening lowlands 

 or swales between chenier ridges support either brackish or salt marshes. 



Natural levees in the lower Mississippi drainage form through the processes 



of reworking depositional materials. Relief is usually less than 2 m (6 ft), 



and width is normally less than 305 m (1,000 ft). Tree growth may be dense on 

 the higher levees (O'Neil, 1949). 



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