Biogeochemistry of Aluminum in McDonalds Branch Watershed, New Jersey Pine Barrens

Abstract

AbstractAluminum concentrations, fluxes, and storage were measured in the vegetation, forest floor, and acid, sandy mineral soil of a forested watershed in the New Jersey Pine Barrens. Volume‐weighted mean Al concentrations in solution increased as water passed through the upland ecosystem, from 0.012 mg L−1 in bulk precipitation to 0.14 mg L−1 in throughfall to 0.45 mg L−1 in E horizon mineral soil, 0.60 mg L−1 in the B horizon, and 0.73 mg L−1 in the C horizon. Weighted mean Al concentration of the stream water was 0.15 mg L−1. Solution Al concentrations in different compartments of the ecosystem were related to the magnitude of moisture flux, dissolved organic carbon concentration, and pH. Soil solution and stream water Al concentrations were high in the winter and spring and low in the summer and fall, inversely following solution pH. Soil solution and stream pH were independent of precipitation pH because of internal control of H+ concentration by the soil and an apparent 0.5‐yr time lag in flushing of atmospherically deposited acids through the soil. Aluminum was partitioned strongly into the lower mineral soil horizons, but large stores of potentially labile Al were found in the upper mineral horizons and forest floor. Standing vegetation represented a relatively small pool of Al but cycled substantial amounts of Al between mineral soil and the forest floor.