The influence of stream water balance on the measurement of stream solute dynamics
Robert A. Payn, Hydrologic Science and Engineering Program / Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois St, Golden, CO 80401, Michael N. Gooseff, Civil & Environmental Engineering Department, Pennsylvania State University, 212 Sackett Bldg., University Park, PA 16802, Brian L. McGlynn, Land Resources and Environmental Sciences, Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, and Steven A. Thomas, School of Natural Resources, University of Nebraska, Lincoln, NE 68583.
The vast majority of stream solute studies treat reach water balance as net behavior, where a gaining or losing reach is determined by the difference between upstream and downstream flow. However, longitudinal or lateral patterns in hydraulic gradients can drive both water gain and loss in the same reach. A more accurate hydrologic characterization of streams might include gross exchanges in reach water balance, where the net gaining or losing behavior is determined by the difference between gross gain and gross loss. The gross loss of water can affect solute concentrations by reducing channel volume and/or velocity and thereby increasing dilution from downstream gross gain. If the constituent gross fluxes of net water balance are neglected, there is potential for incorrectly accounting solute mass removal to biogeochemical activity rather than hydrologic transport. We present a sensitivity analysis with a popular stream transport model (OTIS) to explore the effects of stream water balance on solute modeling. We demonstrate how this transport model accounts for water balance by spatially variable velocity, and show how reactive solute processes might be misinterpreted in gaining streams with gross hydrologic loss.