Evaluation of Manganese Indicators of Reduction in Soil (IRIS).

Indicator of Reduction in Soils (IRIS) tubes can be used to document reducing soil conditions in general (such as wetland restoration soil performance requirements) as well as to specifically address requirements of the Technical Standard of the National Technical Committee for Hydric Soils (related to hydric soils identification and delineation, testing of field indicators, etc). Iron-coated IRIS tubes have been used extensively over the last decade, both because Fe(III) oxides are commonly reduced to soluble Fe(II) in many wetlands, and because procedures have been developed to make Fe-coated tubes. For years researchers have been interested in Mn-coated IRIS tubes, which (based upon thermodynamics) should be able to be reduced, solubilized and stripped under less strongly reducing conditions. Until lately, attempts at making Mn-coated tubes have been largely unsuccessful, due to problems associated with poor adhesion and durability of the Mn-oxide coating. Recent work has led to the development of procedures for synthesizing a Mn-oxide paint that can be used to make Mn IRIS tubes that have durable coatings. The objective of this project was to compare the performance of Mn-coated IRIS tubes with Fe-coated IRIS tubes under a variety of conditions.  Iron-coated and Mn-coated IRIS tubes were installed both in the laboratory (in mesocosms) and under field conditions. Water table levels were either controlled (laboratory mesocosm experiments) or monitored (field experiments), while redox potential (Eh) and pH were also monitored. Results from several lab and field experiments will be reported and discussed, including implications for the use of Mn-coated IRIS tubes.