Salt Marsh Detritus: An Alternative Interpretation of Stable Carbon Isotope Ratios and the Fate of Spartina alterniflora

Abstract

Spartina alterniflora Loisel is the dominant primary producer in salt marshes of the eastern U.S. The role of Spartina in the production of detritus found in marsh soils and waters has been questioned because the carbon isotope ratio of marsh detritus is different from that of living Spartina. We present a hypothesis to explain this paradox. Anaerobic decomposition of Spartina and organic matter from other sources results in the production of energy-rich reduced inorganic sulfur compounds. Bacteria use the energy of these inorganic compounds to fix CO2 from marsh waters. Thus the bacteria obtain their energy but not their carbon from Spartina. In consequence their 8 13C value does not reflect Spartina but is similar to or lower than the values for plankton. Based on energy flow considerations, these bacteria are potentially important contributors to salt marsh detritus and food webs.