The diverse vegetation may be composed of one or more of several plant 

 categories: submergent, floating, emergent, or meadow grasses. The primary 

 productivity of fresh marshes ranges from moderate to high and depends on (1) 

 nutrient availability, and (2) species composition. The latter is controlled 

 by the hydroperiod (depth of water, duration of submergence, and frequency of 

 submergence/emergence). Management practices are designed to regulate water 

 regimes in order to control the biota of an area. These marshes support many 

 animal species which man finds desirable: waterfowl, fish, furbearers, birds, 

 and alligator. 



Delta Marsh 



An ecosystems diagram for the delta marsh is presented in Figure 3-8. 

 The delta marsh ecosystem originates as a series of deltaic islands, dissected 

 by numerous channels or passes. Formation processes have been completely des- 

 cribed (O'Neil, 1949; Morgan, 1972); the phenomena can be simplistical ly viewed 

 as concomitant forces of deposition and subsidence. The marsh that exists 

 depends on the relative magnitude of these two forces. Construction of flood 

 control levees has allowed subsidence to supersede deposition. This allows 

 lakes and bays to merge; water bodies are frequently separated only by the 

 higher portions of levees (Morgan, 1972). Nevertheless, large amounts of sedi- 

 ont may be deposited during floods and effect a change in the dominant vegeta- 

 tion type. Floating, submergent, emergent, and meadow species may be present 

 at any given time; the abundance of each reflects the natural changes in the 

 deltaic processes. 



Unlike the typical fresh marsh, this ecosystem is not nutrient-limited. 

 When the volumninous unidirectional flow of water decreases to a low level in 

 the fall (September-November) of dry years, tidal inundation usually supplies 

 ample materials and energy to the ecosystem. 



The main components of the delta marsh system are the same as those of 

 the fresh marsh. However, the storage of peat and salt in the delta marsh are 

 less important than in the typical fresh marsh. Materials and heat are moved 

 into and through the system via the dendritic branches of the river system. 

 Amounts of materials and heat transported by tidal flows are relatively unimpor- 

 tant. Principal forcing functions from outside the system include drainage 

 alterations (ditching, diking, and canal construction) and pollution. 



Water fluxes . The mean annual discharge of the Mississippi River is approxi- 

 mately 12,750 m3 (450,000 ft3) per second. This flow regime generally follows 

 an annual cycle: a low-water season from late August through November, followed 

 by a relatively long flood period with a peak usually occurring in late April 

 (Gagliano et al., 1971). This flowing water is the main transporter of materials 

 into and out of the system. Indeed, the entire ecosystem depends on and is 

 regulated by this discharge of water with its accompanying sediment and nutrients. 

 The water storage in this system is the same as that discussed for the fresh 

 marsh. 



47 



