In estuarine systems, naturally occurring soluble sulfide can sometimes be present at sufficiently elevated levels to be detrimental to the biota. Concentrations of soluble sulfide in marsh pore water typically are measured using either equilibrium dialysis samplers (peepers) or pore water extractors (sippers). The former technique provides concentrations equilibrated over one or more weeks at cm-scale resolution, while the latter provides instantaneous concentrations, but with a coarser vertical resolution (5-10 cm). We report on a novel technology for documenting marsh pore water sulfide concentrations based on reactive synthetic Fe oxides and image analysis.  Over 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 hydrogen sulfide levels in marsh soil pore water.  The data obtained can provide detailed information with a spatial resolution of mm.