If we assume that accretion has been fairly constant throughout the period of 

 examination and the elevation range of the marsh is small, then the loss of marsh to open 

 water should parallel apparent sea-level rise (Figure 5). If present trends continue, the 

 East Cove marsh will complete its transformation to open water in approximately 40 

 years. 



While the inability of the marsh to maintain its elevation with apparent sea-level 

 rise appears to be an important factor that is responsible for wetland loss in the East 

 Cove marsh, why the marshes are not keeping pace is a more difficult question to 

 resolve. Discharge and sediment load data suggest that the Calcasieu Ship Channel has 

 reduced the amount of riverborne sediment dispersed into the Calcasieu Lake system by 

 debouching flows directly into the Gulf of Mexico (DeLaune et al. in review). The ship 

 channel has also facilitated saltwater intrusion to the Calcasieu estuary which may be an 

 additional interacting factor in wetland loss (Gosselink et al. 1979). 



Probable reductions in sediment supply and saltwater intrusion may only be a part 

 of the problem. The 1.2 cm/yr apparent rise in sea level at Cameron is high. One would 

 expect the rate to be considerably less than at Bayou Rigaud due to the inherently lower 

 subsidence potential, but the rates of rise at the two stations are within 0.1 cm/yr of one 

 another. Nearby gauges depict similar rates which seem to belie any argument that the 

 trends are aberrations due to gauge instability. The similarity in the rates of apparent 

 sea-level rise suggests that interregional factors may be an important if not dominant 

 factor during the past several decades. 



CONCLUSIONS AND STRATEGY 



In both case studies reported here, marsh aggradation has not kept pace with 

 apparent sea-level rise. At the Barataria site, which lies within the Mississippi deltaic 

 plain, basinal processes now dominate over riverine processes and it is apparent that 

 basinal processes cannot maintain marsh elevation given the present rate of apparent 

 sea-level rise. This dominance of basinal over riverine processes is characteristic of the 

 deterioration phase of Mississippi River deltaic cycles (Coleman and Gaglino 1964). 



As an initial step towards narrowing possible management options, we need to 

 determine how widespread marsh aggradation deficits are. The two sites reported here 

 were originally chosen partially on the basis that they were experiencing high rates of 

 wetland loss. Thus, in addition to the small number of sample areas, the sampling is 

 biased. 



If it is found that marsh aggradation deficits are indeed a major component of land 

 loss throughout the coastal zone, then it behooves us to examine why the marshes are not 

 keeping pace in order to propose appropriate mitigating procedures. If the marshes are 

 not keeping pace because canals interrupt sedimentary processes, then management 

 solutions may be weighted towards regulatory procedures. If fluid withdrawals have 

 accelerated subsidence rates, then we must look to reinjection where feasible and 

 possible redistribution and control of groundwater wells. If the marshes are being 

 sediment-starved due to levee systems, then reintroduction of sediments may help, but 

 this solution will be geographicaly limited to a relatively narrow corridor paralleling the 

 present Mississippi River. The possibility that all of these factors can be operating 

 simultaneously dictates that any management plan must be flexible to deal with different 

 causes and adaptable to change as new insights are made. But until we commit our 



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