Soil Solution Composition Relative to Mineral Distribution in Blue Ridge Mountain Soils

Abstract

Abstract Soils with large quantities of gibbsite are normally associated with tropical climates and very intense weathering. The abundance of this mineral in the clay fractions of soils in the temperate climate of the Blue Ridge Mountains raised questions about the soil environment and possible mineral weathering trends. The composition of interstitial soil solutions of three highly weathered soils in the mountains of South Carolina was studied in order to explain contrasting distributions and prevalence of gibbsite and kaolinite. Extensive leaching caused by high amounts of rainfall was evidenced from the low solution ionic strengths and soluble Si content of these soils. The solubility data suggested gibbsite to be the most stable mineral in subsurface horizons serving as Al sinks (mineral precipitation), with kaolinite being more stable in surface horizons. These two minerals appeared to be in a dynamic equilibrium with hydroxy‐interlayered vermiculite, which is controlled by kinetic gradients imposed by site characteristics rather than solution chemistry alone. While the solution composition is consistent with the mineralogical suite of these soils, the residence time of Al and especially Si appears to be the determining factor for secondary mineral formation, weathering transformations, and distribution in the soil profile.