Measurement of Sulfate Reduction in Wetland Soils

Sulfate reduction rates in wetlands have been estimated using numerous techniques. These include the measurement of snlfate disappearance in soil cores and the measnrement of snllide concentration. The direct and most sensitive method used to measure sulfate reduction rates is the nse of radioactively labeled sulfate ( S) (Howarth and Merkel, 1994). This method involves injecting into cores and measuring the amonnt of fonnd. The procednre in which is injected into the soil cores has been used by numerous researchers. Measuring sulfate reduction using this procedure is based on the assumption that the H2 S prodnced from the added is retained as free sulfide, and FeS can be liberated and assayed when the soil is acidified. Measurement of the incorporation of into acid-volatile samples may underestimate snlfate reduction rates because some of the enters sulfur pools that are not acid volatile. It has been shown that an appreciable portion of the reduced is also incorporated into non-acid snlfnr componnds snch as pyrite and elemental sulfur. 

Following stripping of AVS, aqua regia has been used to extract pyrite and elemental forms from sediment. However, it has been determined that the use of aqua regia to analyze for in pyrite and elemental sulfur can overestimate rates of sulfate reduction if nnrednced is not 

Some examples of snlfate rednction rates as a fnnction of depth in marine sediment cores are shown in Fignre 11.11. Connell and Patrick (1968) demonstrated that addition of 200 mg kg snlfate to an anaerobic soil slnrry donbled the rednction rate observed when 100 mg kg snlfate was added. 

The sulfate reduction rate varies greatly among varions wetland ecosystems. Reported sulfate reduction rates in Lonisiana coastal marshes range from 10 to 10 mol SO cm day  

FIGURE 11.11 Sulfate reduction rates in marine sediment profile. (From Iversen and Jorgensen, 1985.) 

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