The total bior.ass of floating, emergent, and meadow type vegetation 

 regulates the level of standing water in the system via evaporation and 

 transpiration effects. 



Floating vegetation not only eliminates subrergents and phytoplankton by 

 shading (Penfound, 1952), but it may become so dense as to significantly inter- 

 fere with oxygen diffusion across the air-water interface (Niitsch, 197G). 



The total vegetation in an area, regardless of its species composition, 

 will contribute to the accumulation of peat and the concomitant decrease of 

 available nutrients. However, the greater the amount of flammable peat and 

 vegetative cover, the greater the effect of a fire in converting unavailable 

 nutrients to available nutrients. 



In addition to providing food for consumers, the plant species may also 

 provide cover. Many of the animals use vegetation for nest construction (birds, 

 alligator, nutria) and/or concealment. 



Consumers . The prir.ary consumers of a fresh marsh may be categorized as 

 terrestrial or aquatic. When one considers the flow of materials and energy, 

 the most important component of the former category is waterfowl. Resident 

 and migrant members alike rely heavily on the floating, subm.ergent, er-ergent, 

 and meadow type vegetation. Chabreck (1971b^) reported that the waterfowl 

 value of fresh rrarshes is greater than that of brackish marshes, which is greater 

 than that of salt riarshes." He believed that this is due to the larger number 

 of species and greater plant coverage in fresh marsh systers. Insects, fur- 

 bearers (nutria, muskrat), and other small mamn'als ingest vegetation, and they 

 are in turn eaten by secondary consumers. Srall fisti, turtles, and invertebrates 

 (crayfish and other crustaceans) comprise the majority of important aquatic 

 primary consumers; they feed on submergents, phytoplankton, and decor posing 

 peat. The survival of such aquatic fauna is directly dependent upon a volume 

 of standing water; toxic substances and low oxygen titers in the water may have 

 detrimental physiological effects. Suspended substances, salinity, and heat 

 may modify the magnitude of these physiological effects. All of these primary 

 consumers use one or more vegetative types for cover and/or nest construction. 



The list of secondary consumers that prey upon prinary consumers includes 

 large fish, wading birds and shorebirds (egret, crane, heron, sandpiper, etc.), 

 alligators, large niammals (raccoon, oppossum, armadillo, etc.), marsh hawks, 

 and insectivorous birds. These animals also use frest, marsh vegetation for 

 cover and/or nest construction. All the marsh consumers return materials and 

 energy to the ecosystem via decomposition of carcasses and feces. 



Summary . Several attributes of the fresh marsh differentiate it from other 

 marsh ecosystems - a large number of plant species, deep water, and low nutrient 

 concentrations. Soils of the fresh marshes are high in organic content due to 

 the accumulation of peat and the lack of marine inputs. Usually the only source 

 of mineral sediment (and its accompanying nutrient load) is upland drainage. 

 Phosphorus is probably a limiting nutrient in many fresh marshes. 



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