Death of the Saw Grass Marsh in the Chenier Plain
Very little biological documentation exists of Chenier Plain habitats prior to the
1930s. However, abundant evidence indicates that the area was substantially fresher thenthan now. Both O’Neil (1949) and a 1951 Soil Conservation Service vegetative type map of Cameron Parish show broad expanses of unbroken saw grass (Cladium jamaicense) marsh (USDA 1951; Figure 30). Saw grass is found in fresh and intermediate marshes and tolerates salinities between 0 and 2 ppt (Penfound and Hathaway 1938). At the time of the 1951survey, saw grass marsh covered approximately 475 mi of Cameron Parish and was the dominant vegetative community. Additional evidence that the Chenier Plain was historically much fresher than it is now includes the following:
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• Cypress trees (Taxodium distichum), with a salinity tolerance of 2 ppt (Chabreck 1972), lined Black Bayou as recently as the 1930s. This is significant because vegetative type maps of 1949, 1968, 1978, and 1988 indicate that much of Black Bayou meandered through brackish marsh, which, due to elevated salinities, could no longer support cypress tree growth (O’Neil 1949; Chabreck et al. 1968; Chabreck and Linscombe 1978, 1988).
• Water from Calcasieu Lake was fresh enough to be used in the irrigation of rice fields in Cameron Parish around 1875-1910 (David Richard, Stream Companies, Inc., personal communication). Water from Calcasieu Lake must have been essentially fresh during this period, because rice is adversely affected by water salinities that exceed 0.6 ppt (Hill 2001).
• In the early 1900s, lower Calcasieu Lake was considered marginal habitat for oysters (Crassostrea virginica) because of the frequency of freshwater and low-salinity events there. Oysters, which inhabit waters within the salinity range of 5-30 ppt (Galtsoff 1964), are now found throughout much of the Calcasieu Lake bottom (USDA 1994).
In contrast to these formerly fresh conditions in Calcasieu Lake, average salinities at fiveCameron Prairie Refuge monitoring stations within Calcasieu Lake ranged from 8.01 to 11.66 ppt during 1994-95. The CSC is undoubtedly the major cause of increased salinity in the Calcasieu Basin.
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