BIOGEOCHEMICAL ORIGIN OF DELTA-S-34 ISOTOPIC SIGNATURES IN A PRAIRIE MARSH

Sulfur isotope ratios were determined in a prairie marsh at Delta, Manitoba, Canada, to determine whether organic matter produced in the marsh had distinctive isotopic signatures. High sulfate levels in sediments from the Delta Marsh arise from high salt concentrations in soils. Sulfate reduction is the major anaerobic metabolic pathway in this sediment system and sulfate diffused into sediment both from deeper soil horizons and from overlying water. Surface water delta(34)S-SO42- values of 15 +/- 1 parts per thousand increased to a maximum of almost 40 parts per thousand in deeper sediment horizons, in marked contrast to sediment pore water delta(34)S-H2S values of 2 +/- 4 parts per thousand. The high degree of discrimination between delta(34)S in sulfate and in hydro(ren sulfide is similar to that found in brackish and marine ecosystems. Emergent macrophytes such as phragmites and cattail had isotopic signatures similar to reduced sulfur in this system. The data from this study suggest that in some nontidal wetland ecosystems, sulfur isotopes may be useful in determining producer-consumer relationships in a manner similar to their application in marine ecosystems.