Seasonal Variation in Solution Composition and Mineral Stability of Two Kentucky Alfisols
Seasonal variations in the soil solution composition of two Maury soils (fine, mixed, mesic Typic Paleudalf) of the inner bluegrass region in Kentucky were investigated by monitoring solution chemistry changes of Ap, Bt, and BC horizons during the spring, fall, and winter of 1988. During the summer, the soils were too dry for soil solution extraction. Temporal soil moisture variations accounted for only a small portion of the variability in solute activities. The resultes demonstrated that, for most solutes, there were significant seasonal differences as well as differences between horizons and between soils. Many solute activities spanned a temporal range of ≈ ±5 times the mean, with Al showing one of the highest (≈10 times) and H4SiO4 one of the lowest (≈3 times) variations. The highest solute activities were attained during early fall and the lowest during the spring or winter seasons. The contrasting behavior of pH and certain solutes (Al, Na, Mn, H2PO4) within and between soils was attributed to stratification effects of the weathered limestone beds. Seasonal fluctuations of Al, Si, Mg, K, and H in solution apparently have moderate effects on illite → vermiculite/smectite → kaolinite weathering relationships, with kaolinite formation being favored during Si-depleted spring periods and vermiculite/smectite during Si-enriched fall (and probably summer) months. Temperature decreases during the winter appeared to enhance the stability of lower order kaolinite, gibbsite, and quartz mineral phases. Even though the consistency of the observed relationships is subject to the uncertainty of the thermodynamic data used and the variability from year to year, the results of this study point out that temporal variations in solution chemistry have indeed a significant impact on chemical weathering and nutrient-availability patterns.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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