Selected Iris tubes installed in Hamar and Ulen soils at Sheyenne National Grassland in Ransom County, ND; Winger and Colvin soils at Hamden Slough National Wildlife Refuge in Becker County, MN; and a Giese soil in St. Louis County, MN. Depth to anaerobic microbial reduction of Fe is indicated by horizontal red line on each tube. Red line represents the soil surface.
Placement of IRIS Tubes
IRIS tubes can be placed in the field at any time of year provided the ground is not frozen. At minimum, pairs of tubes should be installed at any place tests are made. Leave the IRIS tubes in the ground two weeks or more.
Installation of IRIS Tubes
Bore as many holes as needed with a 3/4” soil probe, to a depth of 20” (50 cm). If the soil is saturated or moist the tube is simply pushed into the hole by hand until the tube is seated at the bottom. If the IRIS device is to be installed in dry soil material, fill the hole with water and wait for a few moments to let the water soak in, and then install the tubes. In coarse textured or gravely soil, a bucket auger or spade can be used to dig the hole.Insert IRIS tube so that 1/2'” of oxide coating shows above ground level. Backfill hole as needed and tamp earth lightly around top of tube.
When to Install IRIS Tubes
The time it takes for ferrihydrite to be removed from IRIS tubes depends onwhen during the saturation-reduction process the tubes were installed. If they were installed when the horizon first became saturated, typically during the growing season, the removal time is around two to six weeks. If they were installed at the time of most active reduction, typically April, the removal time could be as short as one week. When no water table is present, the ferrihydrite coating will not be affected or affected very little.
Retrieval of IRIS Tubes
To retrieve the device from saturated or moist soils: gently wiggle the tube to see how tightly the soil holds onto it. Typically, if the device wiggles easily the tube can be removed by pulling it straight out of the ground by hand or with the use of pliers. If the soil holds the tube tightly use a spade to cut the soil on each side of the tube and wiggle the spade back and forth to make a wedge-shaped opening on each side.
Analysis of IRIS Tubes
IRIS devices respond to changes in the redox state of the soil. The soil is saturated and anaerobic when the coating dissolves. Degrees of mottling of the coating mimic the morphology of the soil due to the duration of saturation. When most of the coating is dissolved, the soil is significantly anaerobic. When the coating has a mottled or splotchy pattern, the soil is moderately anaerobic. When the coating does not change, the soil is aerobic.
Click to Download a PDF copy of the IRIS tube Instruction Sheet
INDICATOR OF REDUCTION IN SOILS (IRIS)
Visually Indicates Current Soil Reduction Processes:
- Identify Hydric Soils
- Investigate Depth of Saturation
- Identify Failed Septic Systems
- Analyze Soil Organic Carbon Content.
Scientifically Sound - The NEW STANDARD!
WHAT IT DOES
Indicator of Reduction in Soils (IRIS) tubes are a simple and straightforward, yet reliable, method to help determine if soils are hydric.
HOW IT WORKS
Hydric soils are saturated and anaerobic for some time in most years. In anaerobic soils, microbes reduce and dissolve Fe compounds. IRIS tubes are coated with a naturally occurring Fe compound. Microbial activity in saturated soils will cause part of the coating to dissolve, providing a visual indication that hydric conditions were present. The coatings on IRIS tubes in unsaturated soils will not be affected.
IRIS tubes visibly reflect current hydric soil conditions caused by recent anaerobic processes.
IRIS tubes respond to changes in the redox state of the soil.
- The soil is saturated and anaerobic when the coating dissolves. Degrees of mottling of the coating mimic the morphology of the soil due to the duration of saturation.
- When most of the coating is dissolved, the soil is significantly anaerobic.
- When the coating has a mottled or splotchy pattern, the soil is moderately anaerobic.
- When the coating does not change, the soil is aerobic.
IRIS devices can be used to:
- Identify hydric soils in wetlands
- Investigate depth of saturation
- Identify failed septic systems
- Analyze soil organic carbon content.
Robust and Easy to Use!
Indicator of Reduction in Soil (IRIS): Evaluation of a New Approach for Assessing Reduced Conditions in Soil
By Karen L. Castenson and Martin C. Rabenhorst
In Soil ©, Soil Sci. Soc. Am. J. 70:1222–1226 (2006)
ABSTRACT: Research and management of wetlands often requires the documentation of reducing soil conditions. Documentation of reduction in soils by measuring oxidation–reduction (redox) potentials using Pt electrodes is often difficult because of the time and cost involved in employing these techniques. This study evaluated a new procedure called Indicator of Reduction in Soil (IRIS) that has been recently developed to assist in the detection of reduced soil conditions. Polyvinyl-chloride (PVC) tubes coated with a ferrihydrite paint were inserted into the upper 50 cm of the soil for periods of 12 to 32 d. Soil redox potentials, water table height, and soil temperature were measured concurrently. Upon removal, the tubes were analyzed to assess the loss of ferrihydrite paint from the tube surface. When ferrhydrite paint was substantially depleted from 20% of the area of the IRIS tube, 87% of the observations at the corresponding depth indicated the soil was reduced. When ferrhydrite paint was substantially depleted from 30% of the area of the IRIS tube, essentially all of the soil observations at corresponding depths showed that the soil was reduced. Although not without com- plications, IRIS tubes appear to be a promising new alternative to traditional methods used to identify reducing conditions in soil.
Read the original article
Rabenhorst and Burch
Synthetic Iron Oxides as an Indicator of Reduction in Soils (IRIS) ©, Soil Sci. Soc. Am. J. 70:1227–1236 (2006)
ABSTRACT: Various circumstances in wetland delineation or mitigation strategies require the documentation of reducing conditions in soils. An in- novative approach for assessing reduction in soils known as Indicator of Reduction in Soils (IRIS) has been recently introduced. IRIS tubes are manufactured by coating polyvinylchloride (PVC) pipe with a paint prepared from an Fe oxide (mainly ferrihydrite) suspension. When the iron oxide is synthesized by adding KOH to a FeCl3 solution, the min- eral phase is essentially pure ferrihydrite. Over time, and under par- ticular conditions, the ferrihydrite is transformed to more crystalline forms such as goethite and hematite. The objectives of this study were (i) to assess the mineralogical composition of iron oxide paint synthesized for the manufacture of IRIS tubes and (ii) to assess the significance of mineralogical composition of the Fe oxide paint on desirable qualities for the construction of IRIS tubes. The effects of pH and storage time on the mineralogical alteration of ferrihydrite are exam- ined and compared with performance of the paint by a scale for adhesion and durability. Paint composed of nearly pure ferrihydrite shows poor adhesion and durability. Data suggest that for paint to adhere well to the PVC tubing, the Fe oxide suspension must contain a minimum of 30 to 40% goethite. This desired paint composition can be facilitated during synthesis by titrating the Fe oxide suspension to pH 11 or 12 rather than pH 7.5, which is typically prescribed f0r the formation of synthetic ferrihydrite.
Jenkinson, Franzmeier, and Lynn
Soil Hydrology on an End Moraine and a Dissected Till Plain in West-Central Indiana ©, Copy JES , Soil Sci. Soc. Am. J. 66:1367–1376 (2002).
ABSTRACT: Soil hydrologic properties are a function of precipitation (P)-evapotranspiration relations, stratigraphy, and geomorphology. An understanding of soil hydrology helps us predict many soil and ecosystem properties. We studied soil hydrology on an end moraine and on a dissected till plain in west-central Indiana. We measured hydraulic head, water table level, redox potential (EH ), and temperature, with piezometers (0.25-, 0.50-, 1.0-, 2.0-, 4.5-m depth), observation wells, platinum electrodes (0.25-, 0.50-, and 1.0-m), and thermocouples (0.25-, 0.50-, 1.0-, and 2.0-m), respectively, in soils along two soil toposequences for 9 yr. Water table levels drop rapidly when hardwood trees first leaf out in the spring, and rise rapidly after the trees go dormant in the fall. The Thornthwaite model underestimates evapotranspiration in the forest in the spring. In the dissected plain underlain with dense till, water is held up by the slowly permeable till. Water moves from the interior of the till plain to the dissected bevel where it periodically rises within 1 m of the surface but does not cause redoximorphic features. Soils on the crest of a moraine are similar in morphology to those on the till plain bevel, but have essentially no high water table because there is no upslope contributing area to serve as a water source. In the wetter soils, reduction begins when a soil horizon becomes wet but not saturated, and proceeds more rapidly when the horizon is saturated. There is a lag period of 2 to 8 wk between initial saturation of the soil at 25 cm and minimum EH.
"IRIS Tubes: A Simple, Robust Tool That Promotes the Identification of Reduction in Soil"
Published In CSA News, July 2006
"IRIS Tubes - A New Technology for Documenting Saturation and Reduction in Soils"
Published in National Cooperative Soil Survey Newsletter, May 2006
A Field Tool Visually Indicates Hydric Soil Conditions
Indicator of Reduction in Soils (IRIS) tubes visually reflect current hydric soil conditions caused by anaerobic and reducing processes. This technology provides the user with a device that is easily installed and simple to visually interpret in the field.
IRIS devices can identify hydric soils in wetlands, investigate depth of saturation in soils, identify failed septic systems, and qualitatively analyze soil organic carbon content.
Adopted as National Hydric Soil TECHNICAL STANDARD
The National Technical Committee for Hydric Soils has adopted IRIS tubes as part of the Hydic Soil Technical Standard (HSTS) for identifying anaerobic conditions in soils.
Reliable, robust, and easy to use!