(EGB) Influence of Natural Colloids on Speciation and Chemical Mobility of Trace Metals Transported from Contrasting Watersheds

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9975444ArmstrongWatersheds play a major role in regulating the trace metal status of lakes and streams. Metal export has been related to watershed characteristics, hydrology, and biogeochemical processes through linkages to trace metal carriers, especially suspended particulate matter and natural organic matter. However, understanding metal transport from watersheds requires information on the chemical forms (speciation) of the metals in addition to their yields and concentrations. Of special concern is the nature of aqueous and colloidal metal forms and whether metal bound to aqueous and colloidal ligands (carriers) are labile (bioavailable) or stable. Our premise is that the liability of metals associated with aqueous and colloidal ligands in streams can be characterized and linked to watershed characteristics.Our goal is to quantify and model key chemical forms of trace metals exported from contrasting watersheds and their linkages to watershed processes and characteristics. Specific objective are to (1) determine the partitioning of metals in aqueous and colloidal phases between labile and stable forms and the dynamic behavior of labile forms, (2) quantify prominent characteristics of ligands controlling metal binding and the linkages of these properties to watershed characteristics, (3) rank and quantify the influence of key state variables on trace metal association with aqueous and colloidal phases, and (4) incorporate natural aqueous and colloidal ligands into a framework for medeling the speciation and dynamics of labile metals and the coupling to watershed characteristics and processes.Our approach characterizes the interaction of a suite of trace metals with representative natural aqueous and colloidal ligands from contrasting watersheds. Comparisons among metals will be used to probe ligand properties. Watersheds will be selected to provide specific combinations of key aqueous and colloidal vector (dissolved organic carbon; Fe and Al oxides). A geographic information systems approach will be used to link metal speciation to watershed characteristics and processes.The work is being supported by the Division of Earth Sciences (Hydrology) in the Directorate for Geosciences, the Division of Chemistry and the Office of Multidisplinary Activities in the Directorate for Mathematical and Physical Sciences, and the Division of Chemical and Transport Systems in the Directorate for Engineeing.