Hydrology of sandy soils in northwest Indiana and iron oxide indicators to identify hydric soils

Byron Jeremiah Jenkinson, Purdue University


Because many natural wetlands function as ground water filters in the landscape, wetlands are now protected. Wetlands must have hydric soils, hydrophytic vegetation, and high water tables. We characterized the hydrology and morphology of a soil toposequence that developed on dune and sand plain landscapes in Northwest Indiana as part of the Wet Soil Monitoring Project of Indiana. Soils on low parts of the landscape have hydric morphology, periodically high water tables, redox depletions (gray colors), and supported hydrophytic vegetation. Soils on dunes have deep water tables, lack redox depletions and concentrations, and have upland vegetation. The depth at which soil colors with chroma ≤2 occurred was related to the depth at which the soil was saturated for 5% of the time during the duration of the study, except for the somewhat poorly drained Morocco soil on dune footslope positions, probably because it lacked sufficient free Fe. Water tables are not flat. They are higher under low-lying sand plain than under dunes in winter and early spring, and higher under dunes in the fall. Field studies of soil hydrology prompted a search for a field indicator that, in a simple and straightforward manner, could indicate the level of reduction and anaerobesis a soil had undergone after a period of saturation. We coated polyvinyl chloride (PVC) tubes with the reddish iron oxide ferrihydrite and called it Indicator of Reduction in Soils (IRIS). When an IRIS device is placed in a saturated soil, and the soil becomes anaerobic, the Fe in the reddish oxide is reduced and dissolved, and the white PVC tube is exposed. IRIS tubes installed in various soils in Indiana, North Dakota, and Minnesota visually changed when the soil was saturated and reduced for a time. These changes correlated with other measurements such as depth and duration of water table, Eh measured with platinum electrodes, soil temperature, soil pH, and soil morphology.




Franzmeier, Purdue University.

Subject Area

Hydrology|Environmental science|Soil sciences

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