Wg. Harris et al., EXPERIMENTAL FORMATION OF AQUOD-LIKE FEATURES IN SANDY COASTAL-PLAIN SOILS, Soil Science Society of America journal, 59(3), 1995, pp. 877-886
Coastal-plain Spodosols of the southeastern USA are inexplicably assoc
iated with fluctuating water tables. This study tested hypotheses that
account for water-table influence in Aquod genesis: (i) sand-grain co
atings are released when Fe (a binding agent) is dissolved by organic
acids; (ii) coatings migrate to form an eluvial-illuvial sequence; (ii
i) C and metals accumulate in the illuvial matrix; (iv) imperfectly dr
ained sands are predisposed to podzolization due to low crystalline Fe
; and (V) a minimum solution residence time near the site of acid rele
ase is required. Toeslope and summit positions on hillslopes were samp
led and subjected to physical, chemical, and mineralogical characteriz
ation. 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-l
ike features and on effluent composition. Columns were eluted daily wi
th 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 eluvi
al zones, darkened lamellae, etc.) developed most conspicuously in toe
slope 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 i
n situ methods and indigenous solution components.