Climate change is expected to impact the thermal regimes of streams and otherfreshwater ecosystems (Schindler 2001, Malmqvist and Rundle 2002, Poff et al. 2002). Whileincreased air temperatures will have direct effects on water temperature, indirect effects due tochanges in precipitation patterns, groundwater characteristics, and flow regimes (Perkins et al.2010) may have much larger effects. We explored 1) how variation in hydrologicalcharacteristics of streams mediate their thermal regimes, 2) how geomorphic features ofwatersheds regulated stream water sources and, therefore, thermal characteristics, and 3) whetherpatterns of thermal variation among streams correlate with the life-history characteristics ofPacific salmon that spawn in these aquatic ecosystems.Variation in spawn-timing among salmon populations is influenced by streamtemperature and therefore might also be influenced by hydrological differences related to therelative contributions of snowmelt versus rainfall delivered to streams during spawning and eggincubation periods. We expected that streams receiving more snow sources will be cooler whilerain dominated streams will be warmer. Coastal watersheds in Western Alaska, where themajority of world’s wild sockeye salmon spawn, are expected to receive 25-50% more winterprecipitation and 18-25% more summer precipitation in the next century (Maurer et al. 2007).Future “climate warming” may actually cool streams if the ratio of snow to rain increases forcoastal watersheds. However, the magnitude of the temperature and hydrologic impact willdepend on geomorphology and landscape features (slope, elevation, area, presence of lakes)specific to each stream. Watersheds of a certain size and shape may be able to buffer streamtemperatures against expected changes in air temperature while other watersheds may havegeomorphic characteristics that make them more sensitive to climate change. Salmon may haveto spawn at a different time in many streams to adapt to the changing thermal regimes.We used stable isotopes of oxygen and hydrogen in water collected in 2011-2014 to assessthe relative contributions of rain and snow to stream flows across a gradient of watershedcharacteristics in the Wood-Tikchik State Park and the Togiak National Wildlife Refuge insouthwest Alaska. We also developed statistical models to quantify the effects of watershedcharacteristics on water sources and thermal regimes across the Western Alaska. This work isintended to lay the foundation to support future efforts to link forecasts of climate conditions(rainfall, snowfall, and air temperature) to the thermal conditions that will be experienced byaquatic organisms across this landscape.Given the cultural, economic and ecological importance of aquatic resources in WesternAlaska, there is pressing need to develop scenarios of the trajectories and magnitude of climatedriven changes to aquatic ecosystems in this region. This research will inform efforts to developmanagement strategies for adapting to future warmer climates and to protect the aquaticresources of the region. Because so many terrestrial species are dependent on salmon-derivedresources in this region, our work will also be important for understanding the future impacts ofclimate change on species and habitats dependent on the annual influx of marine-derivedresources.
