112 BIOLOGICAL REPORT 31 



200 



"150 c 



100 



10 20 



30 40 50 60 70 

 Upland area (%) 



-50 



100 



Fig. 6.6. Hypsometric curves for the upland areas of 

 the Buzzards Bay towns of New Bedford and 

 Wareham Adapted from Giese (1989). 



the face of a rising bay. Almost half (47 km 2 ) of the 

 upland surface of Wareham is less than 1 2 m above 

 sea level, while only 1 5% (7 km 2 ) is this low for 

 New Bedford (Fig. 6.6). 



It is possible to determine bay-wide land loss 

 using hypsometric curves for each coastal town in 

 the watershed and the predicted rate of sea-level 

 rise. The major weakness in this method is not the 

 hypsometric approach but the prediction of future 

 water levels (Fig. 6.7). As stated above, at present 

 the eustatic component is about one-third of the 

 total rise (0.09 m out of 0.24 m/100 years). 



Meiei (1989) 

 Gornitzelal (1982) ' 



Oerlemans (1989) -Q 

 Raperelal (1990) '■! 



1 980 2000 



2020 



2040 2060 

 Year 



2080 



2100 



Fig. 6.7. Future sea level projections by various au- 

 thors. Hollow rectangles represent spot estimates, 

 solid triangles mark extreme ends of range estimates 

 Dashed line is the trend if present "assumed" rate of 

 eustatic sea-level rise continues unchanged. Adapted 

 from Emery and Aubrey (1991) 



However, some forecasts of global climate change 

 suggest that this rate may increase several fold over 

 the next 1 00 years. As no accurate value is avail- 

 able, predictions generally use a range of future 

 rise rates encompassing the various models avail- 

 able. Giese and Aubrey (1987) and Giese (1989), 

 using the large range of eustatic rise rates by 

 Hoffman et al. ( 1 986) and local rates of subsidence 

 (Braatz and Aubrey 1 987), estimated land loss from 

 hypsometric curves for each coastal town in the Buz- 

 zards Bay watershed (Table 6.3). The increasing 

 difference in the hectarage from the high versus low 

 estimates of sea-level rise through time results mainly 

 from the increasing uncertainty in long-term predic- 

 tions. In the near term (50 years), however, the dif- 

 ferences between estimates are less than two-fold 

 and with significant loss of upland, about 1 ,000 ha, 

 or 1% of the total land mass. 



In addition to the direct flooding of upland, sec- 

 ondary effects such as increased additional flood- 

 ing during storms, coastal erosion, saltwater intru- 

 sion, and raising of the groundwater table will oc- 

 cur. The impacts on coastal infrastructure will most 

 certainly be disproportionate to the percent of 

 hectarage lost due to the concentration of the popu- 

 lation and development in the low-lying areas di- 

 rectly adjacent to the coast. As stated above, the 

 encroachment of the sea on upland is occurring re- 

 gion wide (Giese and Aubrey 1 987; Fig. 6.8) and 

 indeed throughout most of the world. 



Effects on Saltwater Wetlands. In contrast 

 to effects of relative sea level on uplands, salt marsh 

 area is not necessarily impacted, and in fact, sea- 

 level rise is involved in the maintenance of healthy 

 tidal wetland functioning. The vegetated regions of 

 salt marshes can be divided functionally into high 

 versus low marsh, where high marsh is only inter- 

 mittently flooded and dominated by Spartina pat- 

 ens. Distichlis spicata, and Juncus spp., and low 

 marsh maintains a more intimate contact with es- 

 tuarine waters, being routinely flooded and vegetated 

 by Spartina alterniflora (Redfield 1972; 1967; 

 Nixon 1982; Teal 1986; cf. Chapter 4). 



The distribution of plant communities in tidal 

 wetlands is predominately related to the tidal flooding 



