SIMPLIFIED ANALYSIS OF STREAM SOLUTE TRANSPORT TO DETERMINE CHARACTERISTIC TIMESCALES OF TRANSPORT AND EXCHANGE WITH GROUNDWATER

Advection, dispersion, and transient storage are three dominant solute transport processes in natural stream channels. 1D numerical transient storage models are often used to simulate these processes along with stream flow gains and losses, in order to understand the relative spatial and temporal scales of each process. Here we promote a new approach to determining the influence of advection, dispersion, transient storage, and longer-term exchanges by directly analyzing the solute data collected from stream tracer experiments, with no parameteric modeling required. The inherent challenges of using solute transport models include issues related to model appropriateness and parameter identification. Using this new approach, we are able to parse the timescales and quantity of labeled water (i.e., tracer mass) that experience each process. We are better able to discern the relative influence of advection/dispersion, transient storage, and long time-scale exchange across conditions in a single stream, and across different stream systems. We apply our approach to more than 50 slug injections of dissolved salt in lake-inlet and lake-outlet stream reaches in arctic Alaska, and are able to identify the characteristic transport processes of each reach.