VARIABILITY OF STABLE SULFUR ISOTOPIC-RATIOS IN SPARTINA-ALTERNIFLORA

The sulfur stable isotopic composition of Spartina alterniflora in a l ow salinity tidal creek system was related to differences in porewater sulfur chemistry determined by salinity, hydrodynamics, and season. T he extent of porewater sulfide accumulation, the reoxidation of sulfid e minerals, and sulfate limitation of sulfate reduction were important processes controlling the delta(34)S Of the sulfur available for plan t uptake. The influence of sedimentary sulfate reduction rates on S. a lterniflora delta(34)S was demonstrated in the comparison of 2 sites w ith similar sulfate supply but differing hydrology; plant delta(34)S v alues were heavier where sediments were more oxidized relative to plan t delta(34)S values from a frequently flooded marsh with more reduced sediments The role of sulfate supply in determining S. alterniflora de lta(34)S values was apparent in the comparison of 3 sites with similar hydrology but differing salinity; shoot delta(34)S decreased with inc reasing salinity. In low salinity marshes, oxidation of stored sulfide minerals in winter and spring led to Lighter shoot delta(34)S values, while sulfate depletion in late summer was associated with isotopical ly heavier shoot sulfur. Variability on spatial and temporal scales in sulfur stable isotopic composition of S, alterniflora has implication s for the use of its delta(31)S values in studies of trophic dynamics in estuarine marshes. The sulfur chemistry of the marsh sediments and the sampling season may both influence the stable isotopic signature o f this important primary producer.