Funds are sought to develop and test a new model of solute and isotopic transport in natural waters from karst and non-karst watersheds. This model has the potential to quantify the timescales of transport without ad hoc assumptions about mixing of groundwater and surface water components. In this mathematical model, 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 geochemical constituent. Our basic concept is to study the natural system with perturbations provided by natural processes. In a sense this approach is analogous to the use of earthquakes in seismology to extract information about subsurface structure.
We propose to examine the physical, geochemical and isotopic response of surface streams and springs to storm events with the goal of determining the timescales of complex natural responses. Our preliminary data show that different parameters (streamflow, ionic concentrations, nutrients, sediment, oxygen isotopes, etc.) behave in a qualitatively similar manner, explicable by the model, but that the timescales vary greatly among the natural parameters that collectively define the response of the natural system. We propose several rigorous tests of this new model. First, a review will be made of on-line hydrograph data to test the model in karst and non-karst watersheds. Second, geochemical and isotopic data will be collected from the unimpounded Meramec Basin in eastern Missouri. Access provided by Washington University's Tyson Research Center, located on the Meramec river, will allow intensive sampling at the time intervals required to resolve timescales accurately. Once timescales are established we can begin the work of identifying the reactions (solubility, ion exchange, adsorption, biological uptake, etc.) that control the availability of each constituent. The new approach we propose appears to be applicable simultaneously to diverse geochemical, physical, and isotopic constituents, and has the unique potential to resolve the complexity of natural systems using natural events.
