In this system, the most important water storage is the average water depth, 

 the main regulator of vegetation. Natural subsidence affects this variable 

 via land elevations. Flood protection levees and channel alterations have de- 

 creased or eliminated overbank flow; the result is decreased sediment deposition. 

 Hence, the open ponds become deeper and frequently merge; sometimes only thin 

 strands of levee system remain to partition them (Morgan, 1972). 



The characteristics of saturated soils discussed in the description of 

 fresh marshes are applicable to this system. 



Sediment . In contrast to the highly organic soils of typical fresh marshes, 

 the delta marsh soils are chiefly composed of mineral sediments from upland 

 drainage. Calculations of the average sediment load of the Mississippi River 

 approach three million tons per day (Gaglinao et al., 1971). Before levees 

 and channels were constructed, the accretion of some of this m.aterial counter- 

 acted natural subsidence and actually resulted in the formation of new delta 

 marsh habitat. Presently, however, a significant portion of the sediment load 

 (previously deposited on the delta) flows through the system and is discharged 

 into deeper water in the Gulf of Mexico, where currents carry it in a westerly 

 direction. Notwithstanding this large discharge into the Gulf of Mexico beyond 

 the marsh, regular annual flooding of lower levees deposits a tremendous amount 

 of silt in interdistributary ponds. Delta NWR files indicate that turbidity 

 nd siltation effects are "jery significant factors in controlling vegetation. 



The low organic content of most soils (less than 10 percent) is due to 

 the relatively small amount of peat accumulation which occurs in ponds and other 

 areas of quiet waters (Brupbacher et al., 1973). 



Nutrients . Although the sources of nutrients are the same as discussed 

 in the description of fresh marshes, concentrations of nutrients are greater. 

 The large volunie of water moving through the delta marsh ensures an opulent 

 supply of dissolved and complexed organic and inorganic nutrients. Reactions 

 and mechanisms occurring in saturated soils have been previously discussed and 

 are applicable to this system. 



Primary producers. All of the vegetation types of the fresh marshes may 

 be found within the delta marsh. The largest difference between the two systems 

 is the extreme fluctuation in species composition and abundance in the delta 

 marsh. The vegetative types (floating, submergent, emergent, meadow) and species 

 compositions are controlled primarily by the river discharge and by hurricanes. 

 Thus, dominance by one or more species is ephemeral, and drastic changes in 

 composition may occur within a one-yr period (Valentine, 1970). 



Onsite management practices are minimal in this ecosystem due to the over- 

 whelming forces of the Mississippi River. Past techniques of vegetation manage- 

 ment (grazing, planting, burning) have been aimed at providing food and cover 

 for waterfowl, but they have been largely inconsequential. The vegetation is 

 destined to reflect the constant natural changes within the delta plain that 

 are brought about by the water fluxes. 



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