Variability of stable sulfur isotopic ratios in Spartina alterniflora

The sulfur stable isotopic composition of Spartina alterniflora in a low salinity tidal creek system was related to differences in porewater sulfur chemistry determined by salinity, hydrodynamics, and season. The extent of porewater sulfide accumulation, the reoxidation of sulfide minerals, and sulfate limitation of sulfate reduction were important processes controlling the delta(34)S Of the sulfur available for plant uptake. The influence of sedimentary sulfate reduction rates on S. alterniflora delta(34)S was demonstrated in the comparison of 2 sites with similar sulfate supply but differing hydrology; plant delta(34)S values were heavier where sediments were more oxidized relative to plant delta(34)S values from a frequently flooded marsh with more reduced sediments The role of sulfate supply in determining S. alterniflora delta(34)S values was apparent in the comparison of 3 sites with similar hydrology but differing salinity; shoot delta(34)S decreased with increasing 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 isotopically heavier shoot sulfur. Variability on spatial and temporal scales in sulfur stable isotopic composition of S, alterniflora has implications 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 of this important primary producer.