Indicator of Reduction in Soil (IRIS) devices: A review

Documenting anaerobic conditions is critical for understanding soil processes, identifying hydric soils, delineating wetlands, and managing aquatic resources. Several techniques exist to evaluate the oxidation-reduction status of soils including platinum electrodes, chemical dyes, and analyses of porewater chemistry. Since 2002, Indicator of Reduction in Soils (IRIS) devices have proven a novel, reliable, and cost-effective technique to document anaerobic conditions. This technology involves the application of redox active Fe or Mn oxide based paints onto a durable substrate (e.g., Polyvinyl Chloride pipes or plastic films) which are inserted into the soil. If anaerobic conditions occur during deployment, some or all of the redox active paint will be depleted from the IRIS device surface via chemical reduction and the extent of paint removal can be quantified using a number of approaches. Over the last two decades, IRIS technology has evolved to improve the identification of anaerobic conditions in soils and provide a proxy measure of multiple soil biogeochemical processes (e.g., denitrification, elemental sorption, iron sulfide formation). This review paper provides an overview of developments in IRIS instrumental design and interpretation of results, describes current IRIS applications and benefits, and identifies potential future areas of IRIS device research.