Iron, Copper, and Manganese Complexation by Forest Leaf Litter

Abstract

Abstract Natural and acid-treated leaf litter samples from western white pine (Pinus monticola), willow (Salix Sp.), and chinquapin (Castanopsis sempervirens) and their laboratory-prepared complexes with Fe3+, Cu2+, and Mn2+ were characterized chemically by total metal analysis, infrared (IR) spectroscopy, and electron spin resonance (ESR) spectroscopy. Both the natural and the acid-treated litter samples took up large amounts of Fe, Cu, and Mn from 0.1M solutions, complexing the metals in forms of differing stability against extensive water-washing and proton- or metal-exchange treatments. The IR spectra indicated that carboxyl groups were the most important metal-binding sites in the litter samples. The ESR data showed that the complexes of M2+ involved principally electrostatic forces between the hydrated metal ion and oxygen-containing litter ligands. These complexes were water stable at neutral pH, but easily disrupted by proton or metal exchange. The litter samples bound Fe3+ and, to a lesser extent, Cu2+ in highly water-stable complexes involving direct metal ion contact with oxygen-containing litter ligands. Some of these complexes were resistant to highly acidic conditions or to metal exchange, although reversibility was evident when they were reacted with solutions of differing pH or metal composition. Good correlation existed between trends in total metal content and the ESR data for the metal-litter products obtained after various treatments, suggesting that the metal-litter complexes detected spectroscopically were representative of the dominant speciation of the metals in the litter. For. Sci. 35(4):1040-1057.