The influence of hyporheic exchange on reach‐scale water budgets in a Precambrian Shield catchment, Quebec, Canada

Abstract The influence of hyporheic exchange on water and solute budgets of streams is widely identified as important; yet, there is a notable absence of research identifying its role in Precambrian Shield headwater streams. This research addressed this shortcoming by quantifying the proportions of solute mass loss, net and gross water gains and losses for selected reaches over a single summer recession period. Six conservative tracer injections were performed on nine reaches of a 2.94‐km 2 catchment in Gatineau Park, Quebec, Canada, from July to November, 2011. High solute exchange occurred for all reaches despite most showing positive net discharge. Solute losses in stream reaches typically exceeded 10%, and substantial gross water losses and gains indicate a high degree of bi‐directional water exchange along stream reaches. Both solute loss and the fraction of channel water involved in hyporheic exchange increased throughout the summer in response to a decrease in discharge and increase in the time of contact. Results support the assertion that reductions in groundwater contributions to streamflow throughout the summer baseflow period allow for greater exchange of water through hyporheic flowpaths, which constitute the majority of gross channel losses and gains. Spatial (inter‐reach) variability in mass loss has been previously ascribed to watershed control on exchange potential. In this catchment, net discharge and gross hydrologic gains were inversely related to the average flowpath gradients within the valley bottom and local hillslope contributing areas. Copyright © 2013 John Wiley & Sons, Ltd.