Spatial variations in the sulfur chemistry of salt marsh sediments at North Inlet, South Carolina

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Abstract
Profiles of particulate and dissolved sulfur species have been measured in marsh sediments along three transects across the various growth zones (tall, medium and short) of Spartina alterniflora. In general, organic carbon, total sulfur, pyritic sulfur, pyritization index and dissolved sulfide increased with distance from tidal creek banks, whereas acid volatile sulfur (FeS), pH and Eh decreased with distance. These patterns probably are controlled by spatial variations in belowground production, pore water movement and fiddler crab burrowing. The creekside marsh (tall Spartina) is characterized by lower rates of belowground production (and thus lower rates of sulfate reduction and sulfide production), more vigorous drainage of pore water and more intense fidder crab burrowing as compared to the high marsh (short Spartina). Lower dissolved sulfide concentrations in the creekside marsh are promoted by lower rates of sulfate reduction and removal of dissolved sulfide by drainage at low tide. Higher pH in the creekside marsh is fostered by removal of reduced sulfur (dissolved sulfide by drainage and pyrite by fiddler crab burrowing) which then cannot be oxidized in the sediment to yield acid. The higher pH and lower dissolved sulfide of the creekside marsh, in turn, slow rate of conversion of iron oxide into pyrite in accordance with Rickerd''s (1974, 1975) rate laws and thus foster a lower pyritization index. The lower pyritization index of the creekside marsh also is promoted by fidder crab burrowing which removes pyrite from the sediment and replaces it with fresh oxide from the surface or suspended source. Finally the greater availability of reactive iron oxide in the creekside marsh may shift the relative rates of FeS and FeS2 formation such that a higher steady state concentration of FeS can be maintained there as compared to the high marsh.