Climate change is expected to impact the thermal regimes of streams and other freshwater ecosystems (Schindler 2001, Malmqvist and Rundle 2002, Poff et al. 2002). While increased air temperatures will have direct effects on water temperature, indirect effects due to changes in precipitation patterns, groundwater characteristics, and flow regimes (Perkins et al. 2010) may have much larger effects. We explored 1) how variation in hydrological characteristics of streams mediate their thermal regimes, 2) how geomorphic features of watersheds regulated stream water sources and, therefore, thermal characteristics, and 3) whether patterns of thermal variation among streams correlate with the life-history characteristics of Pacific salmon that spawn in these aquatic ecosystems. Variation in spawn-timing among salmon populations is influenced by stream temperature and therefore might also be influenced by hydrological differences related to the relative contributions of snowmelt versus rainfall delivered to streams during spawning and egg incubation periods. We expected that streams receiving more snow sources will be cooler while rain dominated streams will be warmer. Coastal watersheds in Western Alaska, where the majority of world’s wild sockeye salmon spawn, are expected to receive 25-50% more winter precipitation 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 for coastal watersheds. However, the magnitude of the temperature and hydrologic impact will depend 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 stream temperatures against expected changes in air temperature while other watersheds may have geomorphic characteristics that make them more sensitive to climate change. Salmon may have to 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 assess the relative contributions of rain and snow to stream flows across a gradient of watershed characteristics in the Wood-Tikchik State Park and the Togiak National Wildlife Refuge in southwest Alaska. We also developed statistical models to quantify the effects of watershed characteristics on water sources and thermal regimes across the Western Alaska. This work is intended 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 by aquatic organisms across this landscape. Given the cultural, economic and ecological importance of aquatic resources in Western Alaska, there is pressing need to develop scenarios of the trajectories and magnitude of climate driven changes to aquatic ecosystems in this region. This research will inform efforts to develop management strategies for adapting to future warmer climates and to protect the aquatic resources of the region. Because so many terrestrial species are dependent on salmon-derived resources in this region, our work will also be important for understanding the future impacts of climate change on species and habitats dependent on the annual influx of marine-derived resources.
|ba819405-e538-4836-b620-c769d1d0e570||Riding the crimson tide: mobile terrestrial consumers track phenological variation in spawning of an anadromous fish||mdJSON||ISO 19115-2||HTML|
|ba819405-e538-4836-b620-c769d1d0e570||Association between geomorphic attributes of watersheds, water temperature, and salmon spawn timing in Alaskan streams||mdJSON||ISO 19115-2||HTML|
|ba819405-e538-4836-b620-c769d1d0e570||Watershed geomorphology and snowmelt control stream thermal sensitivity to air temperature.||mdJSON||ISO 19115-2||HTML|