Presentation Title

Mixing of the Willamette and Columbia Rivers across Sauvie Island, Oregon based on stable isotopes (δ18O and δD) of surface water

Abstract

The stable isotopic composition of surface water (δ18O and δD) is used extensively to constrain water evolution throughout the hydrologic cycle. The isotopic composition of meteoric water varies globally based on latitude, elevation, distance from its source, and environmental conditions during and after precipitation. Existing data show that the isotopic signatures of the Willamette and Columbia Rivers are distinct from one another with δ18O values of approximately -10.5‰ and -16.2‰ respectively. Sauvie Island lies at the confluence of these two rivers. It is an 84.8 km2 floodplain containing wetlands, channels, and lakes. I collected water samples throughout the region, including sites upstream of the confluence, downstream, and across Sauvie Island itself. The isotopic composition of collected samples was analyzed to develop a mass-balance model that shows how the rivers mix throughout the study area. Analysis of Sturgeon Lake water samples from Sauvie Island constrain the effect of evaporation on the isotopic composition of river wetlands. This study improves our understanding of the interaction between the Columbia and Willamette Rivers, providing a foundation for future studies of river dynamics along a critical transportation corridor in the Pacific Northwest.

Subjects

Hydrology, Geology

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Mixing of the Willamette and Columbia Rivers across Sauvie Island, Oregon based on stable isotopes (δ18O and δD) of surface water

The stable isotopic composition of surface water (δ18O and δD) is used extensively to constrain water evolution throughout the hydrologic cycle. The isotopic composition of meteoric water varies globally based on latitude, elevation, distance from its source, and environmental conditions during and after precipitation. Existing data show that the isotopic signatures of the Willamette and Columbia Rivers are distinct from one another with δ18O values of approximately -10.5‰ and -16.2‰ respectively. Sauvie Island lies at the confluence of these two rivers. It is an 84.8 km2 floodplain containing wetlands, channels, and lakes. I collected water samples throughout the region, including sites upstream of the confluence, downstream, and across Sauvie Island itself. The isotopic composition of collected samples was analyzed to develop a mass-balance model that shows how the rivers mix throughout the study area. Analysis of Sturgeon Lake water samples from Sauvie Island constrain the effect of evaporation on the isotopic composition of river wetlands. This study improves our understanding of the interaction between the Columbia and Willamette Rivers, providing a foundation for future studies of river dynamics along a critical transportation corridor in the Pacific Northwest.