hydrologic gradient moves groundwater into adjacent coastal marshes where it 

 contributes to the standing-water storage. 



Levees, ridges, and spoil areas have effects on other, more profound, 

 hydrologic aspects of the coastal marshes. Drainage patterns (Chabreck, 1972), 

 water table heights (Chapman, 1960), salinity regimes (Odum, 1967), sedimentation 

 rates (Fisher et al., 1973), and nutrient flows (Darnell, 1976) are regulated 

 by these topographic features. The coastal marsh is a semiaquatic system in 

 equilibrium with the prevailing climatic, hydrographic, geological, and bio- 

 logical forces of the coast, Abrupt changes or even slight modifications in 

 the hydrologic character by alterations of the local topographic relief through 

 dredging and spoiling activities upset the equilibrium and greatly modify the 

 biological characteristics of the system (Fisher et al., 1973; Darnell, 1976). 



The remaining abiotic aspects of the levee, ridge, and spoil bank system 

 involve the same linkages and relative relationships as the abiotic components 

 of the upland ecosystem. These system regulators include soil heat, plant sur- 

 face salts, and nutrient-microbe cycle, leaching of salts and nutrients to the 

 subsoil, fire, and additional aspects of detrital decomposition and incorporation 

 into the soil. The reader is referred to the appropriate sections of the upland 

 model for further information. 



Biotic system . The plant communities of the levees, ridges, and other 

 elevated marsh sites can differ markedly from the surrounding marsh biota. 

 Soil saturation (macropore water), soil oxygen, and soil water salinity are 

 the three primary regulators determining specific plant communities. Plants 

 exhibit an inverse tolerance to soil moisture and soil aeration; soil water 

 salinity can moderate these levels substantially (Penfound and Hathaway, 1938). 



Aggregation of the substrate produces a lowering of the water table and a 

 corresponding increase in soil aeration. Marsh species favored by water- 

 saturated soils are replaced by more efficient species favoring drier, well 

 aerated soils. Under certain circumstances, typical marsh species ( Spartina 

 patens , for example) may invade or occupy high sites if the soil water concen- 

 tration is relatively large and highly saline. Species with less salt tolerance 

 will then be restricted to higher, drier elevations. As salinity levels 

 decrease, the same species will occupy progressively lower elevations where 

 soil moisture levels are greater and soil oxygen levels are lower (Penfound, 

 1952). 



Groundsel ( Baccharis halimifolia ) and marsh elder (Iva frutescens ) are 

 characteristic wood composites which rapidly invade new levees and spoil areas. 

 Under soil conditions of low moisture and moderate to high salinity, such as 

 exist in brackish or salt marshes, these two species may dominate and constitute 

 the climax community. In other instances where the soil's zone of aeration is 

 sufficiently developed and the soil water is virtually fresh, such as in fresh 

 marshes, bottomland sites, deltas, and older cheniers, these early invaders 

 will be replaced by forest seres: for example, live oak scrub, m.aritime forest, 

 or bottomland hardwoods (Wells, 1928; Monte, 1975). 



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