Linking Unsteady Flow, Hyporheic Dynamics And Biogeochemistry In A Glacial Meltwater Stream
Koch, Joshua 1 ; McKnight, Diane 2 ; Neupauer, Roseanna 3
1 INSTAAR/USGS
2 INSTAAR
3 CEAE
Streamflow in the McMurdo Dry Valleys, Antarctica occurs over 12-14 weeks of the austral summer, and is generated by glacial melt. The magnitude of melt depends on the angle of incidence between the sun and glacial surfaces, resulting in a sinusoidal melt hydrograph. This conceptual glacial melt hydrograph is often significantly different from the hydrograph at the gaging station located on the downstream end of the Dry Valley streams. We believe that this difference stems from stream braids and subsurface water storage that occur predominantly in a shallow reach found at similar elevations in many dry valley streams. We constructed a coupled surface water routing and subsurface water flow model of Huey Creek to test our hypothesis. Our model demonstrates the importance of surface / subsurface water interactions in controlling the hydrograph shape. Exchange is from the stream to the subsurface at high flows, and vice versa at low flows. Variable rates of hyporheic storage and exchange underscore the utility of modeling subsurface water flow when considering solute dynamics in unsteady streams. Furthermore, unsteady streamflow and hyporheic dynamics affect water and solute availability, with implications for the microbial and algal mat communities that inhabit these streams.