New laboratory methods developed by the Principal Investigator to characterize the components of surface charge will be applied to benchmark soils from the tropical Americas in order to test their sensitivity and ability to provide reproducible variable-charge measurements that are accurate for highly heterogeneous, structurally fragile mineral mixtures. The project objectives are: (1) to apply a cesium-adsorption method to measure structural surface charge, and (2) to apply new titration and ion adsorption methods to measure variable-charge behavior in highly weathered soils. If these applications prove to be successful, they will provide the basis for a systematic approach to chemical modeling of tropical soils related to their role in continental-scale weathering and the global-scale cycling of chemical elements.
