THE BIO IN ALUMINUM AND SILICON GEOCHEMISTRY

The translocation and transformation of Al and Si are of paramount imp ortance in the processes of primary-mineral weathering, saprolite form ation and soil formation. Geochemical mass balance studies of these pr ocesses have often not considered the important role of the biota in c ycling of these omnipresent soil elements. In the Calhoun Experimental Forest, SC, we found a mean annual biological uptake of Al and Si of 2.28 and 15.8 kg ha(-1) yr(-1), respectively, with a mean annual accum ulation in aboveground biomass of 0.48 and 2.32 kg ha(-1) yr(-1), resp ectively. In the case of Al, net soil leaching from 6 m depth is zero, thus biomass accumulation of Al accounts for the only removal from th e soil system. There is an additional internal system mobilization of Al of 6.6 kg ha(-1) yr(-1), in response to biotic inputs of dissolved organic carbon. In the case of Si, net soil leaching to groundwater is 17.26 kg ha(-1) yr(-1). The accumulation of Si in aboveground biomass , 2.32 kg ha(-1) yr(-1), and in forest floor organic matter, 11.95 kg ha(-1) yr(-1),augments the annual weathering release estimate of Si by an additional 82%. The inclusion of biological cycling of both essent ial and non-essential mineral elements is important for properly evalu ating the biogeochemistry of the earth's crust.