Table 2. Estimates of accretion rates in salt 

 marshes along the Northeastern United States 



Location 



Vegetation type 



Accretion 

 (mm/yr) 



Barnstable Marsh, Cape Cod 

 MA3 



Barn Island, CT , 

 Great Island, CT . 

 Hammock River, CT 



Stony Creek, CT . 



Nells Island, CT^ 



Farm River, CT*- 



Flax Pond, Long Island, 

 fjyd 



Spartina alterniflora "Young marsh" 18.3 



"Older marsh" 1.5-2.7 



S^. patens 



S. patens 



5. patens - Distichlis spicata 



Phraqmites communis 



S^. patens -dwarf S^. alterniflora 



S. alterniflora — ^ 



S. patens (mean 



S. alterniflora 



S^. patens 

 for top 14 cm) 



2.0 

 3.8 



3. 

 17 

 6. 

 6. 

 3. 

 2. 



'Redfield 

 'Harrison 



(1972). 

 and Bloom 



'McCaffrey (1977). 



(1977), 



Tlessa et al. (1977). 



found that a young, actively growing 

 portion of the marsh at Barnstable, 

 on Cape Cod, Massachusetts, increases 

 in elevation at a rate exceeding 

 50 mm/yr. A detailed comparison of 

 accretion rates and sea level rise 

 over time was carried out by McCaffrey 

 (1977) on the high marsh at Farm 

 Creek, near New Haven, Connecticut, 

 by using a Pb^lO.^jatefj core. The 

 results showed that sea level rise 

 was closely matched by marsh accre- 

 tion, and that accretion continued 

 even during short periods of relative 

 sea level fall (Figure 2). However, 

 the more rapid recent rates of sea 

 level rise along the northeast 

 coast are still considerably slower 

 than the average 16 mm/yr that may 

 have occurred during earlier marsh 

 developmient. 



Along the Louisiana coast, where 

 recent subsidence rates have been 

 about 12 mm/yr, extensive measurements 

 by Baumann (1980) have shown that 

 streamside marshes have had sedimenta- 

 tion rates of 15 mm/yr, but that more 

 inland marsh areas have had rates of 

 only 9 mm/yr. As a result, there has 

 been a substantial loss of wetland. 

 It is hard to know if this suggests a 

 natural upper limit of about 10 to 

 12 mm/yr beyond which marshes cannot, 

 on the average, keep pace. The more 

 correct conclusion may be that, given 

 an adequate sediment supply, the marsh 

 grasses themselves are capable of 

 dealing with rapid rates of sea level 

 rise. I do not know how the past 

 sediment supply on the northeast 

 coast compares with the present day 

 supply along the Gulf of Mexico; tidal 



4 



