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Iron speciation in hydromorphic soils derived from red parent materials
Abstract
In the northeastern region of the United States a significant acreage of soils inherited distinct reddish colors due to high iron concentrations. This study aimed to evaluate the chemical, morphological, and micromorphological effects of reducing soil conditions on the speciation of iron minerals through a series of field and laboratory studies. Hematite and goethite were identified as dominant iron minerals in the well-drained and moderately well drained sites. In poorly drained sites, goethite, ferrihydrite, and lepidocrocite were identified. Soil micromorphological observations indicated that well oriented argillans constituted almost 10.8% of the total area in the Bt horizon of the well-drained site. In the poorly drained site, ferrans, iron nodules, and grain cutans were not evident. Qualitative identification of ferrous iron using $\alpha{,}\alpha$-dipyridyl indicator was not possible in the well-drained and the poorly drained sites during the later part of the growing season due to the dryness of the upper part of the soil profile. Red soil material was used in column studies to investigate the effects of different environmental variables on iron speciation. The results indicated that high temperatures, organic carbon, microbial activity, and long saturation periods resulted in a chemically reducing environment. In the column studies, lepidocrocite was identified as a dominant iron mineral. The effect of lactate, hence of organic matter, was evident as a variable affecting Fe reduction. Alternating wetting and drying cycles in columns with lactate solution and treated for more than 14 weeks, resulted in Eh values that were significantly lower as compared to columns which were either treated at shorter time periods or at lower temperatures. Redoximorphic feature development was greater in columns treated at higher temperatures, with lactate solution, and for longer periods of saturation. Ferrous iron was qualitatively identified using $\alpha{,}\alpha$-dipyridyl in all column soils regardless of treatment. X-ray diffraction patterns revealed that the formation of lepidocrocite was related to the presence of chemically reducing conditions. Such environments were simulated in columns treated with lactate solution, higher temperatures, and longer duration.
Subject Area
Agriculture|Geology
Recommended Citation
Mahinakbarzadeh, Mohammad, "Iron speciation in hydromorphic soils derived from red parent materials" (1993). Doctoral Dissertations Available from Proquest. AAI9420660.
https://scholarworks.umass.edu/dissertations/AAI9420660