A Novel In Situ Experimental Setup for Studying the Impact of Bedform Celerity on 2D Oxygen Distribution in the Hyporheic Zone of Streams

Hydrodynamic and morphodynamic forces interacting across the sediment‐water interface control the biogeochemistry in the hyporheic zone. When investigating the redox zonation within streambeds, dissolved oxygen (O 2 ) is considered a key solute to the understanding of river ecosystems. However, no field studies have measured the spatiotemporal O 2 distribution linked to bedform celerity induced by changes in stream water velocity. Therefore, we developed and tested an innovative in situ setup in the River Erpe, Germany. The setup combines a planar O 2 optode and O 2 flow‐through cells for eight sediment depths to capture the variability in O 2 dynamics, and a laser scanner to capture bedform morphodynamics, which was used to calculate bedform celerity. The setup was tested under different stream water velocities between 0.1 and 0.5 m/s. We found that O 2 patterns in the streambed depend on stream water velocity. At low velocities, bedforms were stationary and a stable redox zonation with limited O 2 penetration in the streambed (up to 4 cm) was observed. As we increased the velocity up to 0.3 m/s, the spatiotemporal variability of O 2 distribution across the bedform increased, with anoxic patches moving along the migrating bedforms. At the highest velocity tested (0.5 m/s), the sediment bed was constantly oxygenated with deeper O 2 penetration as compared to slower velocities. The present study provides proof of concept for in situ O 2 measurements in small rivers, which helps to refine laboratory and mesocosm experiments, improve the knowledge of the processes involved in natural environments, and develop more sustainable river management strategies.