Fresh Marsh 



An ecosystems diagram for the fresh marsh is presented in Figure 3-7. 

 Fresh marshes are generally characterized by deeper water, fewer salts, and 

 more numerous species than are brackish or salt marshes. The water flow 

 regime (hydroperiod) controls the phenomena of plant zonation and succession 

 of the classic open-pond/meadow system. Coontail ( Ceratophyllum demersum ), 

 pondweed ( Potamogeton spp. ), and southern naiad ( Najas guadalupensis ) are common 

 submergent species; dense growths of alliqatorweed ( AHernanthera philoxeroides ), 

 water hyacinth ( Eichornia crassipes ), or duckweed ( Lemna minor , Spirodella 

 polyrhiza ) may dominate the zone of floating vegetation. The species composition 

 of the emergent zone is quite variable and may be composed of canes, rushes, 

 and/or sedges, depending upon edaphic conditions. Cattail ( Typha lati folia 

 and X- angustifolia ), roseau cane ( Phragmites communis ), sedges, bulltongue 

 ( Sagittaria falcata ), water hyssop ( Bacopa monnieri ) are common dominants. 

 The meadow marsh zone is typically dominated by grass species such as maiden 

 cane ( Panicum hemitomon ), sprangletop ( Leptochloa fascicularis ), wild millet 

 ( Echinochloa walteri ) or wild rice ( Zizania aquatica ) (Allarri~1950; Penfound, 

 1952; Palmisano, 1970). 



Fresh marshes are frequently more nutrient-limited than are brackish or 

 salt marshes. This is presumably due to the lack of input from saline environ- 

 ments and to alterations of natural drainage patterns (Palmisano, 1970; Bayley 

 and Odum, 1976). However, if adequate phosporous is available, the measurements 

 of primary productivity in fresh marshes may approach those for brackish or 

 salt marsh systems (Keefe, 1972). 



The main components of the fresh marsh ecosystem are storage of water 

 (macropore, micropore, and standing), sediment, nutrients, peat, salt; standing 

 crops of flora (phytoplankton, grasses, emergents, floating mats, and submer- 

 gents); and fauna (primary and secondary consumers). Flows of salt, nutrients, 

 sediments, and gases are moved to and from adajcent systems by flowing water. 

 Forcing functions from outside the system include management practices (ditching, 

 channeling, diking, fire, drawdowns) and pollution. 



Water fluxes . Upland drainage and rain are the sources of water in fresh 

 marsh systems; in addition, they are the primary sources of nutrients (Bayley 

 and Odum, 1976). The inland locations of these marshes prevent inputs from 

 saline environments; however, river delta marshes and marshes subjected to 

 channelization may sporadically be affected by saltwater intrusion, especially 

 during hurricanes. The water inputs into the system must follow one of three 

 pathways: (1) they may percolate into the macropore and micropore spaces of 

 the soil; (2) if the soil is saturated, they may add to the storage of standing 

 water; or (3) they may flow out of the system as runoff. 



Standing water is the crucial storage site In this system; the depth of 

 water and duration of submergence determine the vegetative zonation and succes- 

 sion in a given area. This effect is realized via regulation of the soil 

 moisture, soil aeration, and soil chemistry (O'Neil, 1949; Penfound, 1952; 



42 



