Presentation Abstract

Global warming is expected to dramatically alter the timing and quantity of water within the nation’s river systems; however, these impacts will be heterogeneous both within river basins and across regions. A detailed understanding of the spatial and temporal dynamics of water sources across river networks is therefore central to managing the impacts of climate change. Stable isotopes of water (2H:1H & 18O:16O) provide an emerging method for elucidating the contributions of varying water sources to rivers. Because the stable isotope composition of precipitation varies geographically, variation in the stable isotope composition of river water indicates the volume-weighted integration of source water within the watershed. During September 2017, we collected stable isotope samples across five river networks in the Pacific Northwest and SE Alaska that span a range of hydraulic and climatic conditions: the Snoqualmie, Green, Wenatchee, and Skagit Rivers as well as Cowee Creek. For each basin we regressed isotope values against computed spatial covariates such as elevation, mean annual precipitation, and geology to determine which covariates explained the greatest proportion of isotopic variation. We compared best-fit models for each basin to examine how major correlates of isotopic variation differed among river networks. Results indicate that rivers on the west side of the Cascades display a far stronger relationship to elevation than the Wenatchee. We then built spatial stream network models to display and communicate spatial patterns of isotopic variation within the Snoqualmie and Wenatchee basins. We also employed a mixing-model approach to determine where sources of water in the mainstems of each river originated (e.g. snow zone, rain-on-snow zone, or rain) during summer low flow conditions. Our results can be used by managers and watershed groups to estimate how river flows may shift in a changing climate.

Session Title

Water Quality and Hydrodynamics

Keywords

Stable isotope, Water source, Rivers

Conference Track

SSE1: Habitat Restoration and Protection

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE1-231

Start Date

4-4-2018 2:00 PM

End Date

4-4-2018 2:15 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

McGill_Green.png (43 kB)
Green

McGill_Snoqualmie.png (59 kB)
Snoqualmie

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 4th, 2:00 PM Apr 4th, 2:15 PM

Estimating river flows across basins using water isotopes

Global warming is expected to dramatically alter the timing and quantity of water within the nation’s river systems; however, these impacts will be heterogeneous both within river basins and across regions. A detailed understanding of the spatial and temporal dynamics of water sources across river networks is therefore central to managing the impacts of climate change. Stable isotopes of water (2H:1H & 18O:16O) provide an emerging method for elucidating the contributions of varying water sources to rivers. Because the stable isotope composition of precipitation varies geographically, variation in the stable isotope composition of river water indicates the volume-weighted integration of source water within the watershed. During September 2017, we collected stable isotope samples across five river networks in the Pacific Northwest and SE Alaska that span a range of hydraulic and climatic conditions: the Snoqualmie, Green, Wenatchee, and Skagit Rivers as well as Cowee Creek. For each basin we regressed isotope values against computed spatial covariates such as elevation, mean annual precipitation, and geology to determine which covariates explained the greatest proportion of isotopic variation. We compared best-fit models for each basin to examine how major correlates of isotopic variation differed among river networks. Results indicate that rivers on the west side of the Cascades display a far stronger relationship to elevation than the Wenatchee. We then built spatial stream network models to display and communicate spatial patterns of isotopic variation within the Snoqualmie and Wenatchee basins. We also employed a mixing-model approach to determine where sources of water in the mainstems of each river originated (e.g. snow zone, rain-on-snow zone, or rain) during summer low flow conditions. Our results can be used by managers and watershed groups to estimate how river flows may shift in a changing climate.