Initial Field Installation of Manganese Indicators of Reduction in Soils, Brooks Range, Alaska

摘要

Ten manganese indicators of reduction in soils (MIRIS) and five iron reduction indicator in soils (FIRIS) tubes were installed in a calcareous fen wetland on the south face of the Brooks Range in northern Alaska. Tubes were set in five groups of two MIRIS and one FIRIS across a iandscape transect with hydric soils experiencing high pH/Eh conditions at the wetland, and one set of six MIRIS tubes was installed in a well-drained mid-slope position. The wetland MIRIS displayed oxide paint removal within4 d. whereas the FIRIS installed at the same location for 6 wk (recommended installation interval for FIRIS) displayed <10% oxide removal in four of the five locations and experienced concentration of the iron oxide on the upper 10 cm of the tube. Threeof the five FIRIS also had pyrite (FeS_2) formation on 10 to 20% of their surface areas. After 7 d of installation in the upland, MIRIS did not experience significant removal, indicating that the MIRIS oxide removal in the wetland was due to reduction alone. The rapid removal of MIRIS oxide in high pH/Eh conditions in comparison with the limited removal of oxide from FIRIS supports the idea that MIRIS is a suitable tool to determine the presence of reducing conditions in wetlands unfavorable to Fe reduction. The experiment also showed that pyrite formation on FIRIS should be considered as a proxy for oxide removal in high pH conditions that inhibit Fe reduction.