Browsing by Subject "Redoximorphic features"

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    Characterization and formation of high-chroma features in loamy soils of southern Minnesota
    (2012-12) Pribyl, Douglas Wayne
    High‐chroma features have not been adequately defined under existing terminology or classified under existing systems. The terms “masses” as a subclass of concentrations used in field definitions and “loose infillings” used in micromorpological classifications come closest but are not fully satisfactory. Defined descriptively, high‐chroma features have a typical color of 7.5YR 5/8, are usually less than 1 to 2 mm in diameter, are poorly cemented, and have a sharp external boundary with the soil matrix. They are found in well‐drained to poorly drained soils with first‐appearance typically at depths of 50 to 100 cm. A study was undertaken to more fully characterize and classify high‐chroma features and to provide more accurate interpretations of feature morphology for applications in environmental and soil quality, plant nutrition, and soil genesis. High‐chroma features found within peds having varying degrees of hydromorphic expression were assigned to classes depending on internal color and color patterns. Material removed from features, halos, and the soil matrix was analyzed using a low‐power stereomicroscope, SEM/EDS, TEM/ED, μ‐XRD, ICP, and stain tests to determine properties and composition. Four formation hypotheses are proposed: (1) a non‐pedogenic origin, features having developed from the weathering of an inherited precursor mineral; (2) a pedogenic origin resulting from the formation and infilling of vesicles that formed at depth shortly after deglaciation but are no longer actively forming; (3) a pedogenic origin but features are actively forming; (4) formation by dissolution of a soluble mineral fragment and subsequent infilling of the resulting void, analogous to the formation of a geode. Although high‐chroma features might develop by more than one pathway, a non‐pedogenic origin is favored. Non‐pedogenic hypothesis (1) and the hybrid geodic hypothesis (4) offer the most efficient explanations for the presence of silt, iron, and manganese within high‐chroma features. A proposed weathering sequence based on feature classification and evidence for the presence of manganese nodules in the till‐source bedrock also support a nonpedogenic origin. Pedogenic hypotheses require a sequence of events of uncertain and in some cases seemingly low probability. Existing classification systems offer little insight into genesis. Most importantly, given the evidence for a non‐pedogenic origin, high‐chroma features should not be interpreted or classified as redoximorphic features as the term is typically used in the field. Although high‐chroma features may result from alternating periods of oxidation and reduction, when used alone they are ambiguous indicators of seasonal wetness.
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    Identifying and visualizing the stratigraphy and hydrology of a loess landscape in Southeastern Minnesota
    (2012-09) Beduhn, Rebecca A.
    A total of 44 soil cores were collected and described across a hillslope (approximately 20 hectacres) in southeastern Minnesota within the Major Land Resource Area 105. In 2007, 2008 and 2009, ten piezometers collected water table depths every two hours continuously throughout the growing season. The hydrologic monitoring of the study site was used to associate water depth and duration of saturation to the soil morphology and stratigraphy. This study's objectives are (1) to describe soil profiles and identify redoximorphic features and link them with actual zones of saturation, (2) develop a landscape model of water table depth across the entire hillslope and (3) determine if predictions of water table elevations can be made using certain attributes (slope, plan curvature and profile curvature) of the landscape along with precipitation data. The soil landscape model is a 3-dimensional image of how soil stratigraphy and bedrock interact and influence subsurface hydrologic processes. The prediction of water table elevations are shown by an animation of a selection of data that were generated and manipulated using Avizo, a general-purpose visualization, analysis and 3D reconstruction software. This project is a prelude to a new approach for communicating soil survey information. It was found that the redoximorphic features found on site were contemporary features that were associated with an active hydrology. Animations of the site can provide a tool for education for non-soil scientists to understand landscapes in time and space.