31.2%). Water salinities average 8.2 ppt (range: 1.0 to 18.4 ppt). This marsh type 

 characteristically contains numerous small bayous and lakes. 



The brackish type contains greater plant diversity than the saline type but is 

 dominated by two perennial grasses, Spartina patens and Distichlis spicata (Table I). An 

 important wildlife food plant of brackish marsh, Scirpus oineyi , grows best in tidal marsh 

 free from excessive flooding, prolonged drought, and drastic salinity changes. The 

 species is, however, often crowded out by the domiant grasses, [xirticularly S. patens . 



Intermediate Vegetative Type 



The intermediate vegetative type lies inland from the brackish type and occupies 

 an area of 280,000 ha. This type receives some influence from tides and water salinities 

 average 3.3 ppt (range: 0.5 to 8.3 ppt). Water levels are slightly higher than in the 

 brackish type, and soil organic content averages 33.9%. Plant species diversity is high 

 and the area contains both halophytes and freshwater species used as food by a wide 

 variety of herbivores. Sporting patens dominates the intermediate type as it does the 

 brackish type, but to a lesser degree. Other common plants are Phragmites communis , 

 Sagittaria falcata , and Bacopa monnieri (Table I). 



Fresh Vegetative Type 



The fresh vegetative type occupies the zone inland from the intermediate type and 

 south of the Prairie formation and Mississippi River alluvial plain. In many areas the 

 fresh type is adjacent to or intermixed with forested wetlands (swamp). The fresh 

 vegetative type encompasses an area of 530,000 ha and is equal to the brackish type in 

 size. The type is normally free from tidal influence and water salinities average only 1.0 

 ppt (range: 0.1 to 3.4 ppt). Because of slow drainage, water depth and soil organic 

 content (mean: 52.0%) are greatest in the fresh type. In some fresh marshes, soil organic 

 matter content exceeds 80% and the substrate for plant growth is floating organic 

 matter referred to as flotant by Russell (1942). The type also supports the greatest 

 diversity of plants and contains many species which are preferred foods of wildlife. 

 Dominant plants include Panicum hemitomon , Eleocharis spp., Sagittaria falcata , and 

 Alternanthera philoxeroides . ~~~ ~~" 



COASTAL ALTERATIONS 



Stratification of the Louisiana coastal marshes into distinct vegetative types has 

 historically been maintained naturally by surface features and hydrological processes. 

 The advance inland of saline gulf waters was usually restricted by natural barriers, such 

 as beaches, cheniers, low marsh ridges, and natural levees along streams and lakes. The 

 meandering and shallowing of coastal streams as they moved inland reduced their 

 capacity to carry large volumes of salt water. The discharge of fresh water from inland 

 sources through coastal streams also served to dilute and prevent the inland advancement 

 of saline tide waters. 



Activities of man including leveeing, canal dredging, and stream channelization 

 coupled with natural processes, such as subsidence and erosion, have reduced the 

 effectiveness of saltwater barriers and altered hydrological processes. Canals and 

 channelized streams which connect tidal saltwater sources to inland marshes of lower 

 salinity function in two ways to alter vegetative types. During low tides in the Gulf of 



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