Oxymorphic Manganese (Iron) Segregations in a Wet Soil Catena in the Willamette Valley, Oregon
Segregations of Fe and Mn in soils have been used as indicators of impeded drainage and ensuing periodic saturation. Nine pedons from two catenas were sampled for characterization analyses in support of wet soils monitoring project in the Willamette Valley of Oregon. Manganese/iron segregations [Mn(Fe)] in thin sections were counted in five size classes (>2, 2–1,1–0.5, 0.25–0.5, and <0.05 mm). Segregations in each size class were assigned a nominal area, and the aggregate area for each size class was calculated as a percentage of the area of the thin section. The percentage of thin section occupied by segregations decreases from the wet to the dry end of the catenas. Greatest amounts of large segregations were in E, BE, or AE horizons, directly above B horizons that perch water. A secondary accumulation occurred in Ap horizons. In B and BC horizons some accumulations of large segregations appear to be associated with horizon boundary conditions. More striking in thin section, however is disseminated or fine particulate Mn(Fe) present in the matrix but absent in pores or channels, suggesting these flow zones are loci of reduction. Characterization data on particle size and pore size are used to relate Mn(Fe) quantities to argillation and horizon boundary conditions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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