(0 



> 

 < 



Q 



cr 

 III 



03 



z 



UJ 



> 



3 

 O 



20 40 60 80 100 



BOTTOM EXPOSURE (%) 



Figure 73. 

 year that 



equal or 

 bottom exposure, 

 of 43 ponds and 



Cumulative number of days per 



ponds in the study area will 



exceed certain percentages of 



Based on depth contours 



20 years of tide data on 



the 

 1979 



central Louisiana coast (Chabreck 



Chabreck (1975) questioned the value of 

 most of this effort. However, he 

 acknowledged that burning can be useful to 

 remove a heavy vegetation thatch to allow 

 annual species to germinate and to give 

 three-cornered grass an earlier start 

 during the growing season. Burning is 

 widely practiced to attract snow geese to 

 an area. Trappers find burned areas inuch 

 easier walking, and animal trails are much 

 more noticeable. However^ nutria and 

 raccoon often move from a burned marsh 

 because of the lack of adequate cover. 



Water Qual i ty 



Water quality is a major issue in 

 Louisiana wetlands as in inany other areas 

 of the country, but it has received 

 relatively little attention, probably 

 because the much more pressing issue of 

 marsh loss has taken the spotlight. The 



source of delta sediments, the Mississippi 

 River itself, is heavily polluted with 

 exotic chenicals which become incorporated 

 in the sediments of any marshes created. 



because of 

 hydrocarbon 

 strength; it 

 reintroduced 

 1975). 



here they can be magnified into 



chain, leading to the kind of 



species that 



pelican. That 



from the del ta 



of chlorinated 



on egg shell 



recently been 



From 

 the food 



effects on individual 

 occurred with the brown 

 s|-iecies was extirpated 



the effect 



pesticides 



has only 



from Florida (Blus et al 



Local runoff from urban and 

 agricultural areas is also a serious 

 problem. Seaton and Day (1979), Seaton and 

 Day (1980), and Kemp (1973) documented the 

 effects of urban runoff from the New 

 Orleans area into the Sarataria basin and 

 Lake Pontchartrai n. Gael and Hopkinson 

 (1979) showed that eutrophi cation of water 

 bodies is accelerated by canals which 

 shunt the water around marshes instead of 

 over them. High coliform counts have 

 resulted in oyster bed closures in much of 

 the estuarine area soutli of New Orleans 

 and east of the Mississippi River. In all 

 these examples the primary concern has 

 been with the quality of water in the 

 coastal lakes and bays. If 'iiore runoff 

 water was allowed to flow across the 

 marshes instead of bypassing it through 

 flood drainage canals, it is likely that 

 water quality would improve significantly. 



With all the oil and gas production 

 activity in wetlands, it is surprising that 

 so little is known about the effect of 

 oilspills on wetlands. In the delta only 

 one group of studies is available. This 

 research showed that chronic, low-level 

 oilspills resulted in fairly high levels 

 of hydrocarbons in marsh sediments (Bishop 

 et al . 1976) in the Leeville oilfield. 



These high concentrations are 

 reflected in the aromatic hydrocarbon 

 concentration in tissues of benthic 

 organisms such as oysters and mussels. 

 The emergent grasses and free-swimming 

 organisms such as the grass shrimp and 

 killifish had high concentrations of 

 unresolved hydrocarbon components (Milan 

 and Whelan 1979). The influence of this 

 pollution on biota could not be separated 



96 



