212 



SECT. 10. SEDIMENTATION PROCESSES IN THE ESTUARINE REGION 



At the end of 10.4 you might want to add ... 



Marsh sediments contain more than inorganic matter derived from tidal 

 creeks, though. The vegetation on the marsh surface serves as an 

 autochthonous source of sedimentary material, as most marsh sediments 

 contain 10-90% organic matter. It is not clear how the productivity of 

 these plants may respond to sea level increases or the degree to which 

 transport of organic material from the marsh to the open estuary might be 

 modified by such increases. 



Salt marsh plants contain an appreciable quantity of inorganic 

 material. Table A.l illustrates the composition of some marsh grasses 

 apportioned into aboveground (leaves and stems) and belowground (roots) 

 components . 



Table A.l. Annual Production (g/m'^/yr) of Delaware Marsh 

 Vegetation (Roman and Daiber, 1984) 



Dry Wt. 



Ash 



N 



Total 



6300 



1225 



2457 



63 



For Delaware marshes, the annual production of -6000 g/m^/yr is partially 

 decomposed, partially transported into the open estuary, and partially 

 incorporated into marsh sediments. In Table A. 2 we calculate the amount of 

 marsh grasses that must be incorporated into the marsh sediment to maintain 

 the marsh surface against various rising sea levels without any external 

 inorganic sediment supply, given various grass preservation rates. Such a 

 sediment would probably be characterized as a peat but would contain about 



