A Two-Dimensional Alternative to IRIS Tubes

Documentation of anaerobic conditions in soils is required for the identification of hydric soils as part of wetland determinations. Indicator of Reduction in Soils (IRIS) tubes are tools that can be used to document anaerobic conditions in soils under the technical standards of the National Technical Committee for Hydric Soils (NTCHS). IRIS tubes are lengths of pvc that have a 50 cm section painted with an iron oxide paint. When placed in soil that is actively undergoing reduction, dissolution and removal of the iron oxide paint by iron reducing bacteria occurs. Removal of 30 percent or more of the iron oxide paint indicates anaerobic conditions under NTCHS technical standards. There are several practical challenges to the use of IRIS tubes including the difficulty of painting the round tubes and the susceptibility to removal of the paint by abrasion during transport and installation. Another challenge is the difficulty in accurately determining the percent of paint removed from the round surface of the tube. This study evaluated several alternative two-dimensional media for use with the iron oxide paint. One of the more user friendly systems was weatherproof vinyl banner paper which can be cut into strips, mounted onto thin strips of pvc trim, and are readily inserted into a soil. This system is easily installed, retrieved and analyzed on a flat bed scanner using image analysis software. The strips are also readily stored for future reference. This paper compares these alternative IRIS strips to the traditional IRIS tubes and demonstrates the strengths of this modification to the IRIS methodology.