sand may also be carried onto the 

 marsh by wind and storm overwash. A 

 recent review by Frey and Basan (1978) 

 gave a detailed description of the 



mechanisms 

 movement and 

 marshes, and 

 between some 

 composition 



responsible for the 

 deposition of sediment in 

 I have drawn comparisons 

 aspects of the chemical 

 of marsh sediments and 

 those of fresh water and nearshore 

 marine waters (Nixon 198C). 



Usually high marsh sediments 

 consist of a fine, silt-like inorganic 

 fraction and a coarse organic fraction 

 made up largely of Sparti na roots and 

 rhizomes. As McCaffrey (1977) pointed 

 out, the organic content of marsh 

 soils is only slightly higher than 

 that of many estuarine and nearshore 

 sediments, although their bulk density 

 is much lower. On a dry weight basis, 

 the bulk density of Farm Creek marsh 

 was only 0.2 g/cm (1.01 g/cm wet), 

 while that of the adjacent Long Island 

 Sound sediment was about 0.6 g/cm 

 (McCaffrey 1977). Despite the use 

 of the term "peat" in connection with 

 New England salt marshes, the organic 



content is much lower than freshwater 

 peat bogs, and it would be a cold home 

 that tried to burn high marsh peat in 

 the fireplace. Nevertheless, the 

 dense growth of the Spartina patens 

 roots and rhizomes greatly accelerates 

 the vertical accretion of the marsh 

 through their own volume as well as 

 through sediment trapping; where dense 

 tussocks of the grass develop, the 

 microrelief of the marsh surface is 

 affected (Figure 14). The continual 

 input of new sediment onto the marsh 

 is critical not only for the system to 

 keep up with rising sea level, but 

 nitrogen, phosphorus, and other 

 elements associated with the sediment 

 fertilize the vegetation to maintain 

 the remarkable productivity (DeLaune 

 et al. 1979; Nixon 1980). Though less 

 spectacular than the annual flooding 

 of the great river systems like the 

 Nile or the Mississippi, the daily 

 rise of the tides and the sediments 

 they carry may be just as important 

 for the productivity of these 

 systems as those riverine sediments 

 were for man's early floodplain 

 agriculture. 



|f— S olttrnifloro — ^ 



Spartina pattnc 



^ 



sediment surface 



^.--■■■^ 



m I 



■ ■ 



30 cm 

 20 

 I 

 



Vtrtical Exaggarotion: 2.54X 



Figure 14. Surface microrelief across the transition from low to high marsh at 

 Farm Creek, near New Haven, Connecticut (McCaffrey 1977). Note the effect of 

 Spartina patens tussock development on sediment surface. 



20 



