CONCLUSIONS 



1. Along undeveloped coasts, a rise in sea level drowns the seaward wetlands and allows 

 new wetlands to be created inland as formerly dry land is flooded. However, for the rise in sea 

 level expected in the next century, the area just above sea level available for wetland creation is 

 generally far smaller than the area of wetlands that would be lost. Along developed coasts, there 

 may not be any land available for wetland creation. 



2. Sea level rise could become a major cause of wetland loss throughout the coastal zone of 

 the United States. Assuming that current rates of vertical wetland growth continue and that 

 economic development does not prevent the formation of new wetlands, a five-foot rise would 

 result in 80 percent losses of wetlands in both the South Carolina and New Jersey case studies. In 

 the preliminary nationwide analysis, a five- to seven-foot rise would result in a 30 to 80 percent 

 loss of coastal wetlands. 



3. The coastal wetlands of Louisiana appear to be the most vulnerable to a rise in sea level. 

 The coastal wetlands of the Mississippi River delta are already converting to open water at a rate 

 of 50 square miles per year because of the interaction between human activities, such as 

 construction of levees and navigation channels, and current relative sea level trends caused by 

 land subsidence. Future sea level rise could substantially accelerate the rate of wetland loss and 

 alter the relative advantages of various options to solve the problem. 



4. The impact of sea level rise on coastal wetlands will depend in large measure on whether 

 developed areas immediately inland of the marsh are protected from rising sea level by levees 

 and bulkheads. In the Charleston case study, protecting developed areas would increase the 80 

 percent wetland loss to 90 percent for a five-foot rise. In the nationwide analysis, structural 

 protection would increase the 30-80 percent loss to 50-90 percent. 



5. Factors not considered in this report could increase or decrease the vulnerability of wet- 

 lands to a rise in sea level. This report does not attempt to estimate the change in rates of 

 vertical marsh growth that might accompany a global warming and rise in sea level. 



6. Federal and state agencies responsible for wetland protection should now begin to deter- 

 mine how to mitigate the loss of wetlands from sea level rise. Outside of Louisiana, the most 

 substantial losses are at least 50 years away. However, today's coastal development may largely 

 determine the success with which wetlands adjust to rising sea level in the future. 



7. The prospect of accelerated sea level rise does not decrease the need to implement 

 existing wetland protection policies. Numerous federal, state, and local programs are being 

 implemented to curtail the destruction of the nation's dwindling coastal wetlands. Some people 

 have suggested that because these policies protect wetlands that will eventually be inundated, the 

 prospect of sea level rise is a justification for relaxing wetland protection requirements. However, 

 even from the narrow perspective of a particular parcel of land, this justification ignores the 

 biological productivity that these wetlands can provide until they are inundated, as well as the 

 value of submerged aquatic vegetation that could develop after they are inundated. Moreover, 

 from the broader perspective, even if particular parcels are flooded, society has options for 

 ensuring the continued survival of wetland communities as sea level rises, such as allowing them 

 to migrate inland or promoting their vertical accretion. By protecting today's wetlands, existing 

 programs are helping to keep those options open. 



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