Advances in technology for using Indicator of Reduction in Soils (IRIS) to quantify porewater sulfide levels in the coastal zone

Soluble sulfide is toxic to many plants and animals and is especially problematic in brackish environments of the coastal zone (e.g., marshes and benthic environments). In addition to traditional techniques for measuring porewater sulfide in marsh and subaqueous systems (peepers, sippers, and centrifugal extraction), over the last decade or so, Indicator of Reduction in Soils (IRIS) has been added to the arsenal of available methods. Soluble sulfide reacts with the Fe oxide coatings on IRIS devices to form gray to black iron monosulfide (FeS) stains and coatings, the color of which is a function of both the concentration of the sulfide and the time of exposure. Challenges in using IRIS for sulfide analysis stem from the fact that the dark FeS colors fade quickly over a period of minutes to hours. During the last few years, significant advances in IRIS technology, as well as recent advances in digital image acquisition and image analysis, have allowed us to develop an IRIS approach for quickly and effectively collecting and quantifying porewater sulfide levels in coastal environments (e.g., subaqueous areas and marshes). This article will introduce new tools for deploying IRIS in subaqueous settings and will also demonstrate the utility of the new digital technology for image acquisition and analysis, as sulfide data from two marsh sites and four subaqueous soil sites are presented and discussed.