Experimental Formation of Aquod-like Features in Sandy Coastal Plain Soils
1995
Harris, W. G. | Crownover, S. H. | Comerford, N. B.
Coastal-plain Spodosols of the southeastern USA are inexplicably associated with fluctuating water tables. This study tested hypotheses that account for water-table influence in Aquod genesis: (i) sand-grain coatings are released when Fe (a binding agent) is dissolved by organic acids; (ii) coatings migrate to form an eluvial-illuvial sequence; (iii) C and metals accumulate in the illuvial matrix; (iv) imperfectly drained sands are predisposed to podzolization due to low crystalline Fe; and (v) a minimum solution residence time near the site of acid release is required. Toeslope and summit positions on hillslopes were sampled and subjected to physical, chemical, and mineralogical characterization. Iron dissolution at increasing loading rates of oxalic acid was monitored by batch extractions. A column experiment was conducted to test predisposition and residence-time effects on formation of Aquod-like features and on effluent composition. Columns were eluted daily with oxalic acid (0.001, 0.05, and 0.01 M) under freely drained or 22-h saturation conditions. Ratios of iron/aluminum in oxalic acid extracts were higher at higher loading rates. Iron abundance and crystallinity increased from toeslopes to summits. Aquod-like features (light eluvial zones, darkened lamellae, etc.) developed most conspicuously in toeslope columns, and only for the 22-h residence treatment. Columns most affected released less Fe, Al, and oxalic acid. Results supported our hypotheses for laboratory conditions. Further study is needed using in situ methods and indigenous solution components.
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