Summary . In summary, the salt marsh system is characterized by relatively 

 few species maintaining a high annual primary productivity. This production 

 level is accomplished by seasonal shifts in the major producing components of 

 the system. Grasses dominate in spring and summer, phytoplankton production 

 is greatest during warm months, and production by benthic plants and epiphytes 

 is highest in the winter. The result is a constant supply of detritus, the 

 material which supports the food web of the system. 



Producers, consumers, and flows of material and energy are regulated by 

 tidal phenomena, which also undergo regular temporal changes in magnitude. 



Brackish Marsh 



An ecosystems diagram for the brackish marsh is presented in Figure 3-6. 

 In a long-range time scale of general marsh succession, brackish marshes are 

 expected to precede coastal prairie and more upland-type systems and follow 

 salt marshes (Allan, 1950; Cottam and Bourn, 1952). Several stages of succes- 

 sion may be seen within the brackish marsh system. The number of stages, the 

 duration of each, and the species compositions are geographically variable and 

 highly dependent on local climate and edaphic conditions. Marshhay cordgrass 

 is the characteristic dominant and is frequently codominant with marsh salt- 

 grass. These species are variously associated with sedges, rushes, canes, 

 shrubs, and woody vegetation, depending primarily upon the elevation of the 

 surface. It is the elevation which indirectly regulates several important 

 components of the hydroperiod of a given marsh (Wells, 1928; O'Neil, 1949; 

 Daiber, 1974). The measured productivity of a brackish marsh is less than 

 that of a salt marsh; this may be an artifact of sampling and due to the 

 tendency of smooth cordgrass to form pure stands, where marshhay cordgrass 

 often exists in mixed stands (Keefe, 1972; Henderson and Harcombe, 1976). The 

 brackish marsh is subject to irregular saltwater inundation ranging in frequency 

 from semi-monthly to semi-annually; the extent of inundation is dependent upon 

 wind direction, intensity, and duration (Fisher et al., 1972, 1973). The fresh- 

 water inputs are relatively more important than in the salt marsh system (Cottam 

 and Bourn, 1952). 



The major components of the brackish marsh ecosystem include storage of 

 water (macropore, micropore, and standing), sediment, nutrients, heat, salt, 

 detritus; standing crops of flora (grasses and sedges); and fauna (primary, 

 secondary, and tertiary consumers). Forcing functions from outside the system 

 include water flow (fresh and saline), management practices (impoundments, draw- 

 downs, ditching, fire), and pollution. Sediment, salt, and nutrients are 

 imported from adjacent systems via moving water. 



Water fluxes . Water is of primary importance in the dynamics of the 

 brackish marsh. It is responsible for the transport of materials and energy 

 (nutrients, sediment, heat, salt). Each type of water input (fresh and saline) 

 may be simpl istical ly imagined as coming from opposite directions and counter- 

 acting the magnitude of the other. Thus, relative increases in freshwater 

 effects (via rainfall, storms, or impounding) will be accompanied by decreases 



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