Estimating Climate Risks to River Flows Using Water Isotopes

Lillian McGill collects a water isotope sample from the Tolt River, WA during June 2017

    NW CASC Fellow

  • Lillian McGill , University of Washington,
  • Faculty Advisor

  • Ashley Steel, US Forest Service, University of Washington

Climate change is expected to dramatically alter the timing and quantity of water within the nation’s river systems. Climate change impacts on species and ecosystems will differ within river basins and across regions. In the Northwest, Pacific salmonoids, many of which are listed as threatened or endangered under the federal Endangered Species Act, depend on the distribution of low water flows that provide habitats for rearing young and for migrations, and on the distribution of high water flows that maintain the deposition of spawning gravels. In order to manage Pacific salmon and their habitats in the face of climate change, we need to understand the temporal and spatial variability of water sources within and across entire watersheds.

Stable isotopes provide an emerging method for understanding the contributions of varying water sources to rivers. The purpose of this project is to use stable isotopes to measure and model water chemistry across the Snoqualmie River network to understand current sources of water, as well as broadly characterize isotopic variation across multiple rivers within the Pacific Northwest. This project will provide detailed projections of the quality and distribution of freshwater fish habitats across entire river networks under future climatic conditions. Maps, models and videos developed through this project will allow land managers to design habitat management strategies based on current and future patterns of water source and flow across entire river networks and seasonal cycles.