Preliminary Assessment of Hydric Soil Indicators, Iris Tubes, and Water Table Dynamics in a Northeastern Illinois Wetland.

Indicator of Reduction in Soils (IRIS) tubes were recently added to the National Technical Committee for Hydric Soils (NTCHS) Technical Standards as an approved method for identifying anaerobic conditions in soils.  Research on the effectiveness of IRIS tubes has been positive but limited in geographic extent.  In addition, there is not complete agreement in the literature on the amount of reduction required on IRIS tubes to confirm the presence of hydric soils.  The objective of this study was to evaluate IRIS tubes as an effective method for identifying hydric soil conditions in northeastern Illinois.  A closed depression in northeastern Illinois was selected for study.  The site was previously farmed for over a century but is now part of a wetland restoration program and has had drainage tile removed.   Transects were established running from soils exhibiting hydric soil morphology upslope to soils that did not exhibit hydric soil morphology.  Monitoring wells and IRIS tubes were installed along the transects according to NTCHS specifications.  Data was collected throughout 2008 and 2009.  Soil cores were taken at each monitoring point and their morphology was described and magnetic susceptibility was measured.  Iris tubes were scanned in the laboratory and the percent area reduced was digitally quantified using image analysis software.  Not all soils that met hydric soil indicators met the minimum NTCHS IRIS tube reduction specifications.  Continued IRIS tube analysis and water table monitoring is necessary before any definitive conclusions can be made regarding the minimum percent reduction required on IRIS tubes in these soil-landscapes.