increase along the coast is several times faster than eustatic sea level change for the Gulf of 

 Mexico, which has been estimated to be 0.23 cm/yr (Barnett 1984). Salinity increases occur 

 simultaneously in the coastal marshes. 



Marsh surfaces developing in rapidly subsiding, sediment-deficient environments, such as those 

 in coastal Louisiana, are maintained in the intertidal zone through plant growth, organic detritus 

 accumulation, and limited mineral sediment deposition (DeLaune et al. 1983). The depth of 

 organic layer is determined by the amount of real and local subsidence, eustatic sea level change, 

 organic matter oxidation, and vegetative growth. As plant growth tends to keep pace with the 

 relative rise of sea level, both organic detritus and mineral sediments are entrapped, resulting in 

 the gradual aggradation of the surface (DeLaune et al. 1978). The two processes can be viewed 

 as working in a synergistic manner. Any salinity increase can reduce plant growth and then 

 indirectly affect marsh formation. 



Marsh deterioration along the Louisiana coast is a complex problem and is seemingly the result 

 of numerous factors including salinity. In addition to geological factors, human activities such as 

 canal construction and leveeing are also cited as having an indirect effect on land loss (Craig et 

 al. 1979) by accelerating rates of water-level and salinity increase and storage. 



In addition to salinity increase resulting from subsidence, brine or produced water being 

 discharged into coastal Louisiana can also potentially affect vegetation, marsh stability, and wetland 

 deterioration in regions of discharge. It is estimated that more than 75 million gallons of brine 

 water produced as by-products of petroleum recovery operations is discharged in coastal Louisiana 

 marshes per day. This method is a practice widely used in oil and gas fields in south Louisiana. 

 The produced waters are highly saline, sometimes in the range of 100 to 200 ppt salt concentration, 

 i.e., as much as 5 times greater salt concentrations than the salinity of sea water. Such 

 concentration is likely to be toxic to plants including the most salt-tolerant coastal vegetation. In 

 freshwater areas, brine discharge with salinity levels of less than 5 ppt may be detrimental to 

 vegetation and water quality of the marsh. 



RESPONSE OF LOUISIANA WETLAND PLANT SPECIES TO SALINITY 



Saltwater intrusion and brine discharge along the Louisiana coast can impact survival and growth 

 of wetland species within various habitats. In salt marsh species such as Spartina altemiflora, 

 indirect evidence suggests an adverse effect of high salinity on photosynthesis and growth of this 

 species (Gosselink et al. 1977; Drake and Gallager 1984). In a study of response of S. patens, a 

 dominant brackish marsh species, to salinity, it was found that salt concentrations in the range of 

 22 ppt caused up to 60% reduction in net carbon assimilation rates (Pezeshki et al. 1987b). 

 Results of this study indicated that elevated salinity could potentially reduce productivity of brackish 

 marshes. 



The impact of saltwater intrusion in Louisiana freshwater marshes is expected to be greater than 

 in brackish marshes, assuming comparable salt concentrations since freshwater marshes are 

 composed of highly salt-sensitive species. For example, in Panicum hemitomon, a dominant 

 freshwater marsh species, exposure to saltwater containing 5 ppt salt reduced net carbon 

 assimilation rates 74% and 76% (Pezeshki et al. 1987c). Salt concentration of 12 ppt caused tissue 

 death within 4 days of salt exposure. In Sagittaria lancifolia, another important gulf coast 

 freshwater marsh species, saltwater treatment caused substantial decrease in net carbon assimilation 

 (Table 1). The stomatal limitation of photosynthesis, however, was relatively small, ranging between 



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