THE EFFECTS OF IN-STREAM RESTORATION ON STREAM-GROUNDWATER INTERACTIONS

Recent research on groundwater-stream interactions has focused on understanding spatial variability in hyporheic zone geochemistry across natural morphological units under baseflow conditions. However, few field studies have assessed how spatial variability of hyporheic zone geochemistry is altered due to in-stream restoration. We documented spatial variability in baseflow hyporheic geochemistry and vertical flux rates across a 40 m riffle-pool sequence along Chittenango Creek in Chittenango, NY, USA, immediately before a natural channel design restoration project was completed. We re-sampled after a cross-vane was installed across the riffle bedform as part of the restoration project. For both pre- and post-restoration sampling, we measured streambed temperature over time at 5-cm intervals to a depth of 30 cm and used this data to calculate vertical flux rates at 10 locations across the streambed. We sampled stream and streambed pore water at 15 cm depth at 14 locations. We found that prior to restoration, downward vertical flux rates at 5 cm depth ranged from -0.20 m/d to 0.15 m/d. Higher rates of water movement into the streambed were measured within the riffle bedform, while higher rates of water movement out of the streambed were measured downstream of the riffle and in zones of groundwater discharge. After restoration, downward vertical flux rates at 5 cm depth ranged from -0.15 m/d to 3.40 m/d. High rates of water movement into the restored streambed were found immediately adjacent to the restoration structure. Streambed geochemistry mirrored these water flux dynamics, with high concentrations of nitrate and dissolved oxygen in areas of high downwelling and low concentrations of nitrate and dissolved oxygen in areas of high upwelling or insignificant downwelling.