Biogeochemieal origin of δ34S isotopic signatures in a prairie marsh

Abstract

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 δ34S-SO42− values of 15 ± 1‰ increased to a maximum of almost 40‰ in deeper sediment horizons, in marked contrast to sediment pore water δ34S-H2S values of 2 ± 4‰. The high degree of discrimination between δ34S in sulfate and in hydrogen 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.