BIOGEOCHEMICAL CONTROLS ON ALUMINUM CHEMISTRY IN THE O-HORIZON OF A RED SPRUCE (PICEA-RUBENS SARG) STAND IN CENTRAL MAINE, USA

This study examined the biotic and abiotic processes controlling solution chemistry and cycling of aluminum (Al) in the organic horizons of a northern coniferous forest ecosystem. A mass balance budget indicated that aboveground inputs of Al to the O horizon averaged 0.9 kg ha(-1) yr(-1), with major inputs accounted for by litterfall (69%), followed by precipitation (21%), and net canopy throughfall plus stemflow (10%). Estimated leaching losses of Al from the O horizon averaged 2.1 kg Al ha(-1) yr(-1). We hypothesize that the difference between measured Al inputs and outputs can be accounted for by Al release from weathering of soil minerals admired into the O horizon. Variations in O horizon solution Al chemistry were influenced by a number of factors, including pH, Al equilibria with different solid-phase organic exchange sites, and Al complexation with humic ligands in soil solution.