intermediate values of -16'2 to -17-9 ppt. Marsh soils and to some 

 extent the invertebrate fauna reflected the carbon isotope composition 

 of the major primary producer species in the various zones. 



Five samples of the particulate organic carbon (POC) in marsh tidal 

 water showed &'^^C values of -19-8 to -22-8 ppt. These values fell 

 within the range of 6'K found for offshore POC, most of which is 

 presumed to originate from phytoplankton photosynthesis. This 

 result requires a reexamination of the assumption that the bulk of 

 detrital carbon in Georgia estuaries is derived from S^. alterniflora 

 production. 



A general assumption about the detrital carbon in estuaries has been 

 that most of this carbon is derived from the production of macrophytes. 

 However, Odum and de la Cruz (1967) reported that 95 percent of the 

 particulate carbon in estuarine waters near Sapelo Island was in the 

 nanno fraction and consisted of amorphous particles with no recognizable 

 S^. alterniflora fragments. There is also recent evidence that salt 

 marshes may exhibit a net consumption rather than a net export of 

 carbon. The carbon isotope composition of estuarine POC found in this 

 study further opens to question the source of this carbon. Either 

 a significant fraction of the estuarine carbon is derived from sources 

 other than S^. alterniflora such as phytoplankton production or C-3 

 plant material, or S^. alterniflora carbon present in the nanno fraction 

 of the POC has been fractionated to yield a carbon isotope composition 

 yery different from that of the live plant. (J.B.) 



Keywords: marsh biota, tidal marshes, carbon, vascular plants, 

 marsh ecosystems, productivity, detritus, Georgia 



III-D-6 



Schultz, D.M. and J.G. Quinn. 1971. Studies on the formation of particulate 

 matter from Spartina alterniflora in a salt marsh in Narragansett Bay, 

 Rhode Island. Page 199 in^D.S. Gorsline, ed.. Second national coastal 

 and shallow water research conference; abstract vol. University of 

 Southern California, Los Angeles. (Abstr.) 



Recent studies have suggested that salt marshes are a major source 

 of particulate matter found in estuarine waters. This material, 

 which is thought to be derived largely from marsh grasses, is a source 

 of energy for deposit/filter feeders. There is a net flux of partic- 

 ulate carbon flowing out of the salt marsh, which is considered 

 to be one of the most productive areas in the world. 



A relatively unpolluted salt marsh (Bissel Cove) on the west shore 

 of Narragansett Bay was selected. Particulate matter was collected 

 monthly on both ebb and flood tide, and analyzed for fatty acids. 

 The weight of particulate matter was determined on a dry weight basis 

 and milligrams of particulate matter per liter water and microns of 



113 



