Nevertheless, these restrictions have not curtailed the conversion of wetlands to water. The 

 majority of coastal wetland loss in the United States is now taking place in Louisiana, which loses 

 fifty square miles of wetlands per year, mostly to open water. Navigation channels, canals, and 

 flood control levees have impeded the natural mechanisms that once enabled the wetlands of the 

 Mississippi Delta to keep pace with subsidence and rising sea level. The majority of coastal 

 wetland loss in South Carolina results from impoundments that have converted wetlands to open 

 water during part of the year. 2 



In the next century, moreover, conversion of wetlands to open water may overshadow con- 

 version to dry land throughout the coastal zone of the United States. Increasing concentrations 

 of carbon dioxide and other gases are expected to warm our planet a few degrees Celsius (C) by a 

 mechanism commonly known as the "greenhouse effect." Such a warming could raise sea level one 

 meter or so by expanding ocean water, melting mountain glaciers, and causing polar ice sheets to 

 melt or slide into the oceans. Because most of America's coastal wetlands are less than one meter 

 above sea level, a large fraction of our coastal wetlands could be threatened by such a rise. 



Offsetting this potential threat are two compensating factors. A rise in sea level would flood 

 areas that are now dry land, creating new wetlands. Moreover, wetlands can grow upward by 

 accumulating sediment and organic material. The potential of these two factors to prevent a 

 major loss of wetlands in the next century, however, may be limited. People who have developed 

 the land just inland of today's wetlands may be reluctant to abandon their houses, which new 

 wetland creation would require. Although wetlands have been able to keep pace with the rise in 

 sea level of the last few thousand years, no one has demonstrated that they could generally keep 

 pace with an accelerated rise. 



This report examines the vulnerability of U.S. coastal wetlands (excluding Alaska and 

 Hawaii) to a possible rise in sea level of one or two meters through the year 2100. By coastal 

 wetlands, we refer to marshes, swamps, and other plant communities that are flooded part, but 

 not all, of the time, and that are hydraulically connected to the sea. This chapter, written for the 

 general reader, summarizes the other chapters and their implications, as well as the basis for 

 expecting a global warming and rise in sea level; nature's response to a rising sea; the impacts of 

 human interference with the mechanisms by which wetlands adjust to sea level rise; and policies 

 that might limit future loss of coastal wetlands. 



Chapters 2 (Kana, Baca, & Williams) and 3 (Kana, Eiser, Baca & Williams) describe field 

 surveys that were used to estimate the potential impacts of sea level rise on wetlands in the area 

 of Charleston, South Carolina, and Long Beach Island, New Jersey, respectively. In Chapter 4, 

 Armentano, Park, & Cloonan use topographic maps to estimate the potential loss for 52 regions 

 throughout the United States. Finally, in Chapter 5, EPA's Office of Wetland Protection 

 responds to the challenges presented in the preceding chapters. 



This report leaves unanswered many questions that will need to be investigated for society to 

 rationally respond to the implications of a substantial rise in sea level: What portion of our 

 wetlands will be able to keep pace with rising sea level? In how many areas would it be 

 economical for communities to hold back the sea by erecting levees and bulkheads, at the 

 expense of their wetlands? Should wetland protection policies seek to slow an inevitable loss of 

 coastal marshes and swamps, or to ensure that a particular fraction of wetlands are maintained 

 in perpetuity? 



We hope that this report will stimulate the additional research and policy analysis necessary 

 for society to rationally respond to the risk of wetland loss caused by a rise in sea level. 



