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Comparing spatial and temporal patterns of river water isotopes across networks
Citation:
McGill, L., E. Steel, J. Renee Brooks, AND A. Fullerton. Comparing spatial and temporal patterns of river water isotopes across networks. Society for Freshwater Science Annual Meeting, Detroit, Michigan, May 20 - 24, 2018.
Impact/Purpose:
Much of the water that people living along the Pacific Northwest coast of the USA rely on water from the snowpack in the Cascade mountains, and this snowpack is expected to decrease in coming years. Additionally, these river basins support endangered salmon runs require cold water which stream water originating as snow can provide. We used water stable isotopes to determine the origin of water within 5 watersheds along the Cascades to understand the role of high elevation snow water to summer lowflows within these systems.
Description:
A detailed understanding of the spatial and temporal dynamics of water sources across river networks is central to managing the impacts of climate change. Because the stable isotope composition of precipitation varies geographically, variation in surface-water isotope signatures indicates the volume-weighted integration of upstream source water. We measured the isotope composition of surface-water samples collected during summer low-flow across five basins in the Pacific Northwest and SE Alaska (Snoqualmie, Green, Wenatchee, and Skagit Rivers in Washington, and Cowee Creek in Alaska) to examine spatial variation in surface-water isotopes across a range of hydraulic and climatic conditions. We found mean catchment elevation correlated with surface-water isotopic signatures on the west side of the Cascades and Alaska, explaining 41-92% of variation. Conversely, in the Wenatchee, elevation of the catchment had no predicative power. For this basin we built an alternative model to explain the spatial distribution of isotopic variation and compare it to previously published work in the Marys River. In the Snoqualmie, where elevation explained the highest proportion of isotopic variation, we compare isotopic signatures across the network between early and late summer to explore the spatial distribution of residual snowmelt.