Water levels in these marshes are greatly affected by rainfall, tides, and local 

 drainage patterns. Water levels are typically within 30 cm of the marsh surface with 

 exceptions occurring with storm tides or during periods of excessive rainfall or prolonged 

 drought. The effects of tides are greater in areas nearer the Gulf of Mexico, however, 

 tide levels in the gulf also affect water drainage from interior marshes. In addition to its 

 effect on marsh water levels, tidal action in the gulf also provides a source of highly 

 saline water to the marshes. The daily fluctuating action causes highly saline waters to 

 move inland and mix with advancing fresh water to form a vast estuarine basin. The 

 mixing of salt water from the gulf and fresh water from inland sources provides a 

 horizontal stratifiction of water salinities. Water salinities range from highly saline (20 

 to 25 ppt) near the coastline and gradually decline inland until a zone of fresh water is 

 reached along the northern perimeter of the marsh region. 



Penfound and Hathaway (1939) studied the coastal marsh in southeastern Louisiana 

 and noted that water salinity and water depth were major factors governing plant species 

 distribution. They subdivided the marsh into types on a basis of salt concentration of 

 free soil water, designated these types as saline, brackish, slightly brackish 

 (intermediate), and fresh, and described the plant associations within each type. The 

 marsh types along the entire Louisiana coast were mapped by Chabreck et al. (1968) and 

 Chabreck and Linscombe (1978) on a basis of the plant associations described by 

 Penfound and Hathaway (1939). Chabreck (1972) described the plant species composition 

 and soil and water characteristics of each marsh type. 



DESCRIPTION OF MARSH TYPES 



Marsh vegetative types along the Louisiana coast generally occur in bands 

 paralleling the coastline. The vegetative types are comprised of characteristic 

 associations of plant species with similar salinity tolerances (Table I). 



Saline Vegetative Type 



The saline vegetative type borders the shoreline of the Gulf of Mexico and is 

 subject to daily tidal fluctuations. This type forms a narrow band in the chenier plain of 

 southwestern Louisiana, but is very extensive in the deltaic plain of southeastern 

 Louisiana. The two regions combine to form a total salt marsh area of 270,000 ha 

 (Chabreck 1970). The saline type of the deltaic plain is dissected by numerous 

 embayments and tidal inlets and as a result is exposed to rapid and drastic tidal action. 

 The shoreline of the chenier plain is fringed by an almost continous beach deposit. The 

 beach restricts intrusion of gulf waters, and delays runoff of fresh water. 



Water salinities average 18.0 ppt (range: 8.1 to 29.4 ppt), and soils have a lower 

 organic content (mean: 17.5%) than fresher types located further inland. Vegetation 

 within this type consists of few species. The species are salt-tolerant and dominated by 

 Spartina alterniflora , Distichlis spicata , and Juncus roemerianus (Table I). 



Brackish Vegetative Type 



The brackish vegetative type is further removed from the influence of highly saline 

 gulf waters than the saline type, but is still subject to daily tidal action. The brackish 

 type is a major vegetative type of coastal Louisiana and comprises 520,000 ha. Normal 

 water depths exceed that of saline marsh and soils contain higher organic content (mean: 



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