The Mississippi Delta and Texas Chenier Plain wetlands appear to be the most vulnerable. 

 As Table 1-5 shows, 36 percent of the latter would be lost in the low scenario, and all could be lost 

 in the high scenario. Abandonment would increase the portion of wetlands surviving the next 

 century by about 15 percent of today's acreage. Armentano et al. estimate that 80 and 97 percent 

 of Louisiana's wetlands would be lost for the low and high scenarios, respectively. However, we 

 caution the reader that their model did not consider the potential positive impacts of a diversion 

 of the Mississippi River, which could enable a fraction of the wetlands to survive a more rapidly 

 rising sea level. 



Although the Pacific Coast wetlands examined appear to be as vulnerable to sea level rise as 

 Atlantic and Gulf coast wetlands, Armentano et al. found that the former have greater potential 

 for wetland creation with sea level rise. In the Califomian study areas, 35 to 100 percent of the 

 existing wetlands could be lost; however, the net loss would be 1 to 18 percent if developed areas 

 were abandoned. 



The Pacific Northwest study site could experience a tenfold increase in wetland area for 

 either scenario, if uplands are abandoned. However, we suggest that the reader not attribute 

 undue significance to the Columbia River results. This study site accounted for less than 5 per- 

 cent of the Pacific Coast marshes considered. The result is a useful reminder of the fact that 

 some areas could gain substantial amounts of wetland acreage. We do not recommend, however, 

 that any of the regional results be taken too seriously until they can be verified by additional 

 study sites and a more detailed examination of wetland and upland transects, such as those in 

 Chapters 2 and 3. 



Nationwide Estimate 



The results of Armentano et al. can be used to derive a rough estimate of the potential 

 nationwide loss of coastal wetlands. However, the reader should note that Armentano et al. did 

 not use a completely random method for picking study areas, and that their elevation estimates 

 were rounded to the nearest quarter meter. Thus, they warn the reader that estimates based on 

 their projections are not statistically valid. 



Armentano et al. sought to include study sites for all major sections of coast. However, they 

 did not attempt to ensure that the wetland acreage of the sites in a particular region are directly 

 proportional to the total acreage of wetlands in that region. Therefore, to derive a nationwide 

 estimate of the loss of wetlands one should weight estimates of "percentage loss by region" by 

 actual wetland acreages in the various regions. 



A recent study by the National Ocean Service estimates coastal wedand acreage by state 

 (Alexander, Broutman, and Field 1986). We modified those estimates to exclude swamp acreage 

 in regions where Armentano et al. did not investigate swamps. The term "coastal wetland" in this 

 report refers to tidal wetlands and non-tidal wetlands that are hydraulically connected to the sea, 

 such as cypress swamps in Louisiana. The NOS study includes all swamps in coastal counties, 

 some of which are well inland and not hydraulically connected to the sea, particularly in North 

 Carolina and New Jersey. 



The first column of Table 1-7 shows the adjusted estimates of wetlands acreage by region. 

 Because the Pacific Coast wetlands represent such a small fraction of the total, we have combined 

 the California and Pacific Northwest regions. The rest of the table shows the implied wetland 

 losses and gains estimated using the percentages reported by Armentano et al. The greatest 

 losses would appear to be in Louisiana and the southern and middle Atlantic coast. However, we 

 caution the reader that the region-specific estimates have less credibility than the nationwide 

 estimate. 



Of the estimated 6.9 million acres of coastal wetlands, 3.3 million could be lost under the 

 low scenario. If human activities do not interfere, however, 1.1 million acres might be created. 

 Under the high scenario, 5.7 million acres (81 percent) would be lost, while 1.9 million acres 

 could potentially be created. 



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