The Origins of Detritus in Georgia Salt Marsh Estuaries

The current view that estuarine food chains are in large part supported by influx of plant detritus from bordering tidal wetlands may not be correct for all cases. In Georgia estuarine ecosystems, salt marshes dominated by the cordgrass, Spartina altaerniflora Loisel., are thought to be the major source of particulate detritus in the estuarine waters. However, I present three lines of evidence which suggest that Spartina detritus may not form a significant fraction of the organic seston in Georgia estuaries: 1) For Spartina salt marshes, attempts to document the net loss of plant material to the estuary have yielded contradictory results. 2) The stable carbon isotopic composition of organic seston in Georgia coastal waters does not match the isotopic composition of Spartina carbon; however, the seston 1'C/12C ratios are compatible with phytoplankton or terrestrial detritus sources. 3) Estimates of potential input of organic materials to Georgia estuaries of 770 g m-2 yr-1 by phytoplankton and 600 g m-2 yr-1 by terrestrial plant matter are of the same magnitude as the hypothetical detritus input of 780 to 1660 g m-2 yr-1 from the Spartina salt marshes. A revision of the concepts about the role of salt marshes in estuarine production may be in order.