these results for an area with a different tide range but similar species occurrence, such as Sapelo 

 Island (Georgia), the flooding frequency for 5. virginica could be used to estimate its modal 

 elevation at the locality. With a mean tide range of 8.5 ft at Sapelo, S. virginica is likely to occur 

 around +5.3 ft MSL (based on substitution of the tide range in Figure 2-7B). This procedure can 

 be applied for other southeastern U.S. marshes as a preliminary estimate of local modal 

 elevations. 



We do not consider elevation results for the transects to be definitive because of the 

 relatively small sample size. However, the results are sufficiently indicative of actual trends to 

 allow scenario modeling. With the tide-probability curves presented, it should be possible to 

 check these results against other areas with similar climatic patterns, but different tide ranges. 



CONCLUSIONS 



Our results appear to confirm the hypothesis that there would be less land for wetlands to 

 migrate onto if sea level rises, than the current acreage of wetlands in the Charleston area. 



Wetlands in the Charleston area have been able to keep pace with the recent historical rise 

 in sea level of one foot per century. However, a three- to five-foot rise in the next century resulting 

 from the greenhouse effect would almost certainly exceed their ability to keep pace, and thus 

 result in a net loss of wetland acreage 



The success with which coastal wetlands adjust to rising sea level in the future will depend 

 upon whether human activities prevent new marsh from forming as inland areas are flooded. If 

 human activities do not interfere, a three-foot rise in sea level would result in a net loss of about 

 50 percent of the marsh in the Charleston area. A five-foot rise would result in an 80 percent loss. 



To the extent that levees, seawalls, and bulkheads are built to prevent areas from being 

 flooded as the sea rises, the formation of new marsh will be prevented. We estimate that 90 

 percent of the marsh in Charleston— including all of the high marsh— would be destroyed if sea 

 level rises five feet and walls are built to protect existing development. 



This study represents only a preliminary investigation into an area that requires substantial 

 additional research. The methods developed here can be applied to estimate marsh loss in 

 similar areas with different tidal ranges without major additional field work. Nevertheless, more 

 field surveys and analysis will be necessary to estimate probable impacts of future sea level rise on 

 other types of wetiands. 



The assumptions used to predict future sea level rise and the resulting impacts on wetland 

 loss must be refined considerably so that one can have more confidence in any policy responses 

 that are based on these predictions. The substantial environmental and economic resources that 

 can be saved if better predictions become available soon will easily justify the cost (though 

 substantial) of developing them (Titus et al. 1984). However, deferring policy planning until all 

 remaining uncertainties are resolved is unwise. 



The knowledge that has accumulated in the last twenty-five years has provided a solid 

 foundation for expecting sea level to rise in the future. Nevertheless, most environmental policies 

 assume that wetland ecosystems are static. Incorporating into environmental research the notion 

 that ecosystems are dynamic need not wait until the day when we can accurately predict the 

 magnitude of the future changes. 



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