Timescales of Geochemical and Isotopic Transport in Natural Waters

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0106925Criss A new model of solute and isotopic transport in natural waters is being refined and tested. This model can quantiy the timescales of transport without ad hoc assumptions, about ixing groundwater and surface water components. Based on diffusion theory, storm events are treated as "delta functions" that induce a complex series of geochemical and physical responses. The transport equations are readily transformed into linear versions whose intercepts accurately retrodict the timing of the storm events, and whose slopes reveal the time constants for transport of each creochemical constituent. The basic concept is to study the natural system with perturbations provided by natural processes. Information gained onthe geochemical and isotopic response of surface streams and springs to storm events would determine the timescales of complex natural responses. Data colllected in the first stage of this project show that different parameters (ionic concentraions, total dissolved organic compounds, nutrients, sediment, oxygen isotopes, etc.) have in a qualitatively similar manner, explicable by the model, but that the timescales vary greatly among the parameters that collectively define the response of the natural system. Rigorous tests of this model will be conducted withgeochemical and isotopic data collected from several sites within an unimpounded river basin (the Meramec Basin, eastem Missouri). This endeavor will be facilitated by an autosamplerinstalled a karst spring at Washington University's Tyson Research Center, and a new autosampler nearby on the Meramec River. These programmable devices will allow intensive sampling to resolve timescales accurately, and will permit detailed comparisons of simultaneous groundwater and riverine responses to precipitation events. Key questions concerning the sources, the reactions (solubility, ion exchange, adsorption, biological uptake, etc.), the migration paths, and the timescales of pollutant and pathogen transport through surface and near-surface environments will be explored. The new approach appears to be applicable to diverse geochemical, physical, and isotopic constituents. It has the unique potential to resolve the complexity of natural systems using natural events.