Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The rivers flowing through the Amazon Basin are both physically and chemically heterogeneous. Through detailed geochemical analyses, this study indicates that variability is primarily controlled by substrate lithology in the source region and the erosional regime. Observations suggest that it is possible to classify the chemical composition of Amazonian rivers according to the geochemistry of the soils in their catchment regions and vice versa.;The ability of microorganisms to undergo chemical exchanges with their aqueous environment, involving both the uptake and excretion of various elements, has been overlooked as an important factor in determining the chemistry of Amazonian rivers. Silicon extracted and precipitated by diatoms indicate that the dissolved silicon levels of the Rio Negro are in part controlled by biological activity. In the Rio Solimoes, both filamentous algae and bacteria were shown to bind and accumulate significant amounts of dissolved metals. In a solute-rich river system, the metal-loaded microorganisms play an important role in the transfer of metals from the hydrosphere to the sediment. It is not difficult to imagine that algae and bacteria could effectively cleanse the water of dissolved metals and partition them into the sediments.;In the Amazon Basin, many of the rivers are characterized by their high organic content and their solute-deficiency. In the Rio Negro, major cations such as Fe, Al, and Si are significantly bound into organo-metallic complexes, contributing largely to the mobilization and transport of these metals in the river. The high organic-inorganic matter ratio of this river also seems to provide sufficient reactive sites for the adsorption of trace metals. This process may cause significant changes in the overall chemical composition of rivers.;Lastly, anthropogenic forces now influence the nutrient dynamics of the forest system. Results indicate that numerous metals are released as aerosols through the combustion of vegetation. In addition, an entire suite of metals are concentrated in the residual ash, which potentially can be dispersed into the atmosphere. Analyses of radiogenic isotopes (Sr, Pb) in rainfall suggest that these emissions may provide nuclei for the condensation of water vapor, with the net result being a high concentration of dissolved metals in the precipitation. (Abstract shortened by UMI.)



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