The pore waters of sediments from a salt marsh along the Delaware estuary have been analyzed for sulfur species and associated trace metals. Since the sediment interface is usually in contact with the atmosphere, the sulfur species are dependent on the production of hydrogen sulfide by sulfate reduction and subsequent oxidation by diffusing oxygen. The most important species observed are hydrogen sulfide, polysulfide ions and thiosulfate. Secondary reactions of hydrogen sulfide and polysulfides with decomposing organic matter yield significant concentrations of both thiols and organic polysulfides. Upon isolation of the sediment from the atmosphere due to tidal inundation, bacterial sulfate reduction becomes the dominant process. This results in the reduction of the polysulfides in agreement with thermodynamic predictions, and suggests that the redox couple sulfide/polysulfide is a good redox indicator under such reducing environments. The concentrations of trace elements Cu and Fe in the pore waters are mainly controlled by sulfide formation. Calculations show that copper is strongly complexed probably with organo-sulfur ligands. Iron might be complexed as such sulfur species to a much lesser extent than copper.