WEATHERING DYNAMICS FROM SELECTED SOIL SITES ON BARRO COLORADO ISLAND, PANAMA

Weathering is an important factor influencing nutrient cycling and carbon dioxide fluctuations in the soil ecosystem. Soil weathering controls the availability of nutrients and metals needed for a fertile soil environment. Soil development and weathering is particularly intense in tropical climates. We examined biological, chemical, and mineralogical changes in soil properties on Barro Colorado Island, Panama during the wet and dry seasons and as a function of land use changes using a tropical forest vegetation setting and an adjacent plot that has been converted to grassland vegetation. Soil pits 1 meter in depth were sampled every 5 cm and characterized for soil organic matter content, determined by the Walkley-Black method, soil moisture, and total lipid biomass to assess the soil quality. X-ray diffraction was used to determine mineralogical changes in the soil and a sequential extraction method was used to assess trace metal mobility. Forest soils exhibit higher organic matter content than grass soils regardless of soil moisture. Total lipid biomass characterization of the active soil microbial population reveals fluctuating trends in the dry and wet seasons with higher amounts under the forest vegetation. The mineralogy varies between kaolinite, smectite, and iron oxides and is typical of a soil weathering profile from basaltic parent material. The mineralogical profile suggests that soil development has progressed more rapidly in the forest system. Trace metal mobility varies significantly between the forest and grass profiles, with oxide mineralogy and abundance responsible for the observed trends.