The elevated cheniers, levees, and spoil areas function as important 

 regulators of the hydrologic regimes in adjacent marsh and estuarine systems, 

 provide roosting and resting sites for wildlife, and serve as transportation 

 avenues for the "invasion" of wetlands by terrestrial organisms. Structurally, 

 the system combines wetland and terrestrial vegetation, and it typically sup- 

 ports abundant above-ground biomass (Bahr et al., 1977). As such, then, these 

 elevated systems become transitional zones between the maritime woodland or 

 upland grasslands and the coastal marshes. Depending on the location of a 

 specific levee or ridge system, it may support xeric marsh or hydric forest 

 components. Regardless of its specific location, the successional direction 

 of the biotic elements is toward the upland ecosystem. Several key abiotic 

 factors regulate the rate and extent of this movement; these are soil oxygen 

 (Penfound and Hathaway, 1938; Penfound, 1952; Walker and Collier, 1969), 

 elevation (Penfound and Hathaway, 1938; Wells, 1928), soil mosture (Kerwin and 

 Pedigo, 1971); and soil water salinity (Penfound and Hathaway, 1938). These 

 parameters and other regulating functions are discussed below. 



Like the upland ecosystem, the conceptual model of this system consists 

 of two primary components: the abiotic system and the biotic system. Funda- 

 mental interactions between these components are similar to those of the upland 

 model . 



Abiotic system . The abiotic system receives external inputs (driving 

 forces) in the forms of sunlight, atmospheric water and gases, surface water 

 from upland drainage (Bourn and Cottam, 195C) and occasional tidal inundation 

 (Penfound and Hathaway, 1938), gulf salt spray (E. Odum, 1971; Au, 1974), tran- 

 sported sediments (Fisher et al., 1973), and groundwater flowing through a 

 hydrologic gradient. Additional system inputs, such as nutrients and detritus, 

 are received from the biotic community occupying the site. The abiotic system 

 provides outputs as flows that regulate community development; these outputs 

 include soil gases, soil moisture, soil salts, plant surface salts, nutrients, 

 and soil heat. Finally, certain outputs of the abiotic component are lost from 

 this system, at least temporarily, to become potential inputs to adjacent eco- 

 systems such as the coastal marshes. System losses include evaporated water, 

 leached nutrients and salts, transported detritus, surface-water runoff, and 

 most significantly, eroded soil materials. Transported soil materials re- 

 leased by erosion contribute to increased water turbidity and sedimentation 

 rates in adjacent aquatic systems (Darnell, 1976). 



As in the upland ecosystems, the abiotic component of the levee system is 

 dominated by one important subsystem, the hydrologic cycle. This cycle regu- 

 lates the critical edaphic parameters of aeration, moisture, and salinity, 

 which in turn determine the specific nature of the producer component. It is 

 therefore essential to consider the hydrologic cycle in detail, pointing out 

 the factors which regulate flows within and between systems, describing the 

 function of each output, and relating the hydrology of this system to surround- 

 ing systems. 



The particular hydrologic characteristics of levee, ridge, and spoil 

 systems may vary considerably between types depending on elevation, parent mate- 

 rial and the nature of the surrounding ecosystems. The primary sources of water 



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