Armentano et al. estimate that the low scenario would have relatively little impact on New 

 England's marshes, largely due to their ability to keep pace through peat formation. Neverthe- 

 less, peat formation would not be likely to keep pace with the more rapid rate of sea level rise 

 implied by the high scenario, which could result in two-thirds of these marshes being lost. Similar 

 situations could be expected in Florida and the Northeast Gulf Coast, although a flatter coastal 

 plain in these regions would offer a greater potential for wetland creation if development did not 

 stand in the way. The assumption by Armentano et al. that Florida wetiands could accrete one 

 centimeter per year may be unduly optimistic. 



The middle and southern Atlantic coastal marshes would be more vulnerable than New 

 England to the low sea level rise scenario, largely because smaller tidal ranges there imply that 

 existing wetlands are found at lower elevations than the New England wetlands, while vertical 

 accretion was generally assumed to be less than in the case of Florida and the Northeast Gulf 

 Coast. These estimates appear to imply less wetland loss than the case studies by Kana et al. In 

 the high scenario, however, estimates by Armentano et al. are considerably higher and more 

 closely consistent with Kana et al., as we discuss below. 



To understand the implications of Armentano et al., it is useful to compare their procedures 

 and results with those of Kana et al., where there is site-specific information. In the case of 

 Charleston, Armentano et al. estimate that the low scenario (net substrate change, 111 centi- 

 meters) implies a 37 percent loss and a 21 percent gain through 2100, for a net loss of 16 percent. 

 The transects of Kana et al. imply that the low scenario would result in a 100 percent loss of 

 existing marsh with an 18 percent gain, for a net loss of 82 percent. Had the Armentano et al. 

 approach been applied to the Charleston case study, it would have attributed an initial elevation 

 of 1.0 meters to the marsh, 12 which is not unreasonable given that it ranges from 0.5 to 1.3 

 meters— although 80 percent of the marsh is below 1.0 meters. However, their procedure would 

 require the net substrate change to be one meter plus one-half the tidal range, for a total rise of 

 1.8 meters, before the marsh would convert to water. Thus, the model of Armentano et al. 

 estimates Charleston's wetlands to be much less vulnerable than the field surveys by Kana et al. 

 suggest. 13 



In the case of the New Jersey wetlands, the groups arrived at similar results. Armentano et al. 

 estimate a 75 percent wetland loss through 2075 in the high scenario and no loss in the low 

 scenario, while Kana et al. estimate an 86 percent loss in the high scenario and a 6 percent gain 

 in the low. The tendency of Armentano et al. to assign a fairly high elevation to the marsh is more 

 appropriate in areas where high marsh dominates. Moreover, five-foot contours were available in 

 this case. Table 1-6 summarizes the Armentano et al. and Kana et al. findings. 



TABLE 1-6 



COMPARISON OF ARMENTANO ET AL. AND KANA ET AL. STUDY RESULTS 

 SHOWS THAT USE OF TOPOGRAPHIC MAPS CAN UNDERESTIMATE 

 VULNERABILITY OF WETLANDS TO SEA LEVEL RISE (percent loss of wetlands) 



1 These results are derived from the profile estimated by Kana et al. 



27 



