Hydric soil determination using IRIS tubes, soil morphological features, and monitoring wells at a northern Illinois wetland.

摘要

Hydric soil identification is necessary for wetland delineation and other development purposes. Criteria for hydric soils are defined by the NRCS, although hydric soils are mainly identified in the field using the NRCS hydric soil indicators. These indicators rely largely on soil color at a given depth. IRIS tubes have recently been developed as a method to determine reducing conditions in soils. An IRIS tube is a PVC tube coated with iron oxide paint and installed into soil. A significant amount of paint will be removed from the tube when reducing conditions are present. The intent of this research is to compare methods of determining hydric soils. The study was conducted at a wetland within the DuPage County Forest Preserve in Bartlett, IL. Datapoints were established along two transects from wetland to upland areas. Groundwater monitoring was conducted at each point. Soils were classified and evaluated for the presence of NRCS hydric soil indicators. IRIS tubes were installed in two groups, the first for 4 weeks, and the second for 5 months. Paint removal from IRIS tubes was evaluated in three ways: from the entire tube, the upper 12 inches of the tube, and according to the NTCHS criteria. The study was conducted over the 2008 growing season to determine a relation between the presence of reducing conditions when using soil taxonomy, hydric soil indicators, IRIS tubes, and groundwater well readings. At the wetland points, soils generally met NTCHS IRIS tube criteria for reducing conditions, displayed one or more hydric soil field indicators, and had wetland hydrology. Upland points generally did not meet these criteria. Soils in the transitional zones between wetland and upland areas met one or more criteria, but results varied. In IRIS tube evaluation, results varied between visual estimates and those determined using Image Tool software. Estimates of paint removal also varied between participants evaluating IRIS tubes. As difficulties were presented scanning images of round tubes, use of flat surface for IRIS evaluation is suggested.