Synthetic Iron Oxides for Documenting Sulfide in Marsh Pore Water

Abstract

In estuarine systems, naturally occurring soluble S2− is an indicator of anaerobic decomposition by the SO42−reduction pathway and can, at high concentrations, be detrimental to plant communities. Depth distributions of soluble S2− in marsh pore water are typically measured using either equilibrium dialysis samplers (peepers) or pore water extractors (sippers). The former technique provides concentrations equilibrated over one or more weeks at centimeter‐scale resolution, while the latter allows rapid sampling and analysis but with a coarser vertical resolution (5–10 cm). We report on a novel technology for documenting marsh pore water S2− concentrations based on reactive synthetic Fe oxides and image analysis, which allows rapid sampling but still captures small‐scale spatial resolution. During the last few years, this new technology associated with synthetic Fe oxides known as IRIS (Indicator of Reduction In Soils) has been developed to aid in documenting reducing conditions in wetland soils. Our recent work has shown that IRIS technology can be used to document and measure H2S levels in marsh soil pore water. The data obtained can provide detailed, quantitative information on S2− concentrations with millimeter‐scale spatial resolution.