Chemical Weathering Soil Profiles of the Rio Chagres Watershed
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University School of Earth Sciences. Shell Undergraduate Research Experience (SURE) Internships. 2008
Chemical weathering is a major process in the development and resultant bulk chemistry of soils, yet little research has been done in moist tropical climates investigating the relationship between the chemistry of soil and extent of weathering as related to depth. For this research project, two sample soil pits were dug in the Rio Chagres watershed in central Panama, and 13 samples from each soil pit were collected at approximately 12 cm increments from surface to close to bedrock. The soil pits were located directly above a gabbro and a greenstone, two of the dominate lithologies of the basin. Analysis for this research project was done by grain size and carbon and nitrogen analysis, and by use of X-ray fluorescence spectrometry (XRF) to measure major and trace elements present. Calculation of the Chemical Index of Alteration (CIA) and Vogt’s index of weathering (V) were also completed to evaluate degree of weathering as related to depth to establish an accurate weathering profile for each pit. In Pit 1, located above the gabbro, grain size decreases and weathering index increases with depth, suggesting a greater influence of subsurface groundwater during weathering. In pit 9, located above the greenstone, grain size fluctuates with depth and is overall more course than in pit 1, and the weathering index is highest at the surface and decreases with depth. This represents a more traditional and expected weathering profile, with the greatest weathering occurring at the surface. Future research is needed to provide a more continuous data set as well as information on trace element behavior in these profiles.
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