Initial Field Testing of Manganese Reduction Indicators for Soils (MRIS) in a Calcareous Fen.

Ten manganese reduction indicators for soils (MRIS) and five iron reduction indicator in soils (IRIS) tubes were installed in a calcareous fen on the south face of the Brooks Range in northern Alaska.  Tubes were set in five groups of two MRIS and one IRIS across a landscape transect with hydric soils experiencing high pH/Eh conditions at the wetland, and one set of six MRIS tubes was installed in a well-drained mid-slope position.  The wetland MRIS displayed oxide paint removal within four days, whereas the IRIS installed at the same location for six weeks (recommended installation interval for IRIS) displayed <10% oxide removal in four of the five locations and experienced concentration of the iron (Fe) oxide on the upper 10 cm of the tube.  Three of the five IRIS also had pyrite (FeS₂) formation on 10-20% of their surface areas. After seven days of installation in the upland, MRIS did not experience significant removal, indicating that the MRIS oxide removal in the wetland was due to reduction alone.  The rapid removal of MRIS oxide in high pH/Eh conditions contrasted to very little removal of oxide from IRIS supports the idea that MRIS is a suitable tool to determine the presence of reducing conditions in wetlands unfavorable to Fe reduction.  The experiment also shows that pyrite formation on IRIS should be considered as a proxy for oxide removal in high pH conditions that inhibit Fe reduction.