Modeling the Impact of Stream Discharge Events on Riparian Solute Dynamics

The biogeochemical composition of streamwater and the surrounding riparian water is mainly defined by the exchange of water and solutes between the streamand the riparian zone. Short‐term fluctuations in near stream hydraulic headgradients (e.g., during streamflow events) can significantly influence the extent and rate of exchange processes. In this study, we simulate exchanges between streamsand their riparian zonedriven by streamstage fluctuations during single streamdischarge events of varying peak height and duration. Simulated results show that strong streamflow events can trigger solute mobilization in riparian soils and subsequent export to the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased durations significantly enhance solute export, however, peak height is found to be the dominant control for overall mass export. Mobilized solutes are transported to the streamin two stages (1) by return flowof streamwater that was stored in the riparian zoneduring the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in long tailingof bank outflows and solute mass outfluxes. We conclude that strong streamdischarge events can mobilize and transport solutes from near streamriparian soils into the stream. The impact of short‐term streamdischarge variations on solute exchange may last for long times after the flow event.