Nutrients. Significant nutrient sources in the brackish marsh include 

 exogenous dissolved organic and inorganic materials (from fresh and saline 

 water), detritus, and bottom sediment. The relative contributions of each 

 differ with the location and climate of a given area. Because these marshes 

 are infrequently inundated by tides, the nutrient contribution from saline 

 sources is less in brackish marshes than in salt marshes. The significance of 

 this contribution depends on (1) the volume of freshwater input and (2) the 

 concentrations of nutrients in the fresh water. 



Nutrient transformations between unavailable and available forms are similar 

 to those described for a salt marsh. It must be emphasized, however, that the 

 brackish marsh is not inundated daily by tides. Areas may be flooded or exposed 

 for short or long periods, depending primarily upon elevation, rainfall/evapora- 

 tion rates, and management practices. Nutrient regeneration is accomplished 

 by bacteria acting on detritus and other particulate organic material. Nitrates 

 and phosphates are released for plant utilization in aerated soils. Submergence, 

 however, changes the oxidation-reduction systems and the microbial populations 

 which are active. The result is biological production of ammonia rather than 

 of nitrate. Also, the reduced forms of inorganics (magnesium, manganese, iron, 

 potassium, calcium) predominate; these forms are generally more available to 

 plants than the oxidized forms (Redman and Patrick, 1965; Brupbacher et al., 

 1973; De Laune et al., 1976). 



Primary producers . The vegetation of brackish marshes is typically domi- 

 nated by marshhay cordgrass. Saltgrass is the most commonly found associate 

 and may codominate in more saline soils (Allan, 1950). 



The rough mat formed by the dead culms of these species is an effective 

 self-preservation mechanism (Blum, 1968). Competition from other species is 

 insignificant unless this mat is removed by fire, storms, or mechanical means 

 (Lynch et al., 1947; McNease and Glasgow, 1970; Smith, 1970; Hess et al., 1975). 

 Pure stands of rushes and sedges ( Scirpus spp.) may be locally abundant in lower 

 wet areas. These subdominants have a narrower salinity range than marshhay 

 cordgrass or saltgrass and their competitive advantage is dependent upon the 

 levels of standing water and temporal variation (Babcock, 1967; Palmisano and 

 Newsom, 1968; Rossa and Chabreck, 1972). Furthermore, when stands of sedges 

 do manage to thrive, they are selectively consumed by waterfowl, muskrat, nutria, 

 and cattle (Lynch et al., 1947; O'Neil, 1949; Chabreck, 1968). Hence, the 

 natural fluctuation of various environmental factors favors marshhay cordgrass 

 as the climax species. 



Although the primary productivity of mashhay cordgras/sal tgrass is generally 

 less than that of smooth cordgrass, it is still very impressive. Henderson 

 and Harcombe (1976) report values between 1,300 and 1,900 g/m2/yr for the gulf 

 coast. By comparison, the production of phytoplankton is insignificant. However, 

 the phytoplankton comprise an important food source for aquatic invertebrates 

 and small fish. 



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