INVESTIGATING THE EFFECTS OF HYDROLOGIC RESTORATION ON WATER FLUX ACROSS SAUVIE ISLAND, OREGON

This work investigates the effects of hydrologic restoration efforts at Sturgeon Lake, OR on water flux and sedimentation. Restoration work involved reopening a channel connecting Sturgeon Lake to the Columbia River. In this study, we use stable isotopes (δ¹⁸O and δ²H) of meteoric water to determine the sources and evolution of water in the area, comparing results from before and after restoration. We hypothesize that the restoration channel has increased surface water flux, and in turn reduced dangerous levels of sedimentation and stagnation. The 3,200-acre lake is a pivotal environmental feature in this area, providing a haven for juvenile salmon on the Columbia River during high flow periods and improving their survivability upon reaching the ocean. The Oregon Conservation Strategy (OCS) names this area as one of the most important stopovers in the Pacific Flyway, providing winter habitat for hundreds of thousands of waterfowls and migratory birds. Based on our analysis of δ¹⁸O and δ²H, Sturgeon Lake shows a strong evaporative signature, with a local meteoric water line slope of 5.53, significantly less than the Global Meteoric Water Line. We estimate that Sturgeon Lake had experienced >50% evaporation, suggesting ongoing stagnation is significant. Further, Sturgeon Lake was composed of ~58% Willamette and ~42% Columbia waters at the time of analysis (summer 2019). Ongoing work is being done using spatial variations of precipitation and long-term seasonal measurements of Sturgeon Lake and source water end-members, providing more insight into residence time and evaporation on annual time scales. Though our preliminary results from summer suggest stagnation is still significant, winter and inter-annual data is needed to determine whether the restoration canal has achieved its goal. Canals such as the one dredged by the WMSWCD are one of the primary methods by which natural hydrology may be restored to Sauvie Island, making it vital that we understand their efficacy, and whether further efforts are necessary.