Volume 35, Issue 3 e14063
RESEARCH ARTICLE

Spatiotemporal dynamics of water sources in a mountain river basin inferred through δ2H and δ18O of water

Lillian M. McGill

Corresponding Author

Lillian M. McGill

Quantitative Ecology and Resource Management, University of Washington, Seattle, Washington

Correspondence

Lillian M. McGill, Quantitative Ecology and Resource Management, University of Washington, Seattle, WA 98105, USA. Email: [email protected]

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J. Renée Brooks

J. Renée Brooks

Pacific Ecological Systems Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon

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E. Ashley Steel

E. Ashley Steel

School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington

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First published: 27 January 2021
Citations: 13
Funding information Department of the Interior Northwest Climate Adaptation Science Center graduate fellowship; National Science Foundation Graduate Research Fellowship, Grant/Award Number: DGE-1762114

Abstract

In mountainous river basins of the Pacific Northwest, climate models predict that winter warming will result in increased precipitation falling as rain and decreased snowpack. A detailed understanding of the spatial and temporal dynamics of water sources across river networks will help illuminate climate change impacts on river flow regimes. Because the stable isotopic composition of precipitation varies geographically, variation in surface water isotope ratios indicates the volume-weighted integration of upstream source water. We measured the stable isotope ratios of surface water samples collected in the Snoqualmie River basin in western Washington over June and September 2017 and the 2018 water year. We used ordinary least squares regression and geostatistical Spatial Stream Network models to relate surface water isotope ratios to mean watershed elevation (MWE) across seasons. Geologic and discharge data was integrated with water isotopes to create a conceptual model of streamflow generation for the Snoqualmie River. We found that surface water stable isotope ratios were lowest in the spring and highest in the dry, Mediterranean summer, but related strongly to MWE throughout the year. Low isotope ratios in spring reflect the input of snowmelt into high elevation tributaries. High summer isotope ratios suggest that groundwater is sourced from low elevation areas and recharged by winter precipitation. Overall, our results suggest that baseflow in the Snoqualmie River may be relatively resilient to predicted warming and subsequent changes to snowpack in the Pacific Northwest.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are openly available in the EPA ScienceHub at http://doi.org/10.23719/1520140.

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