Changing Conditions In The Yukon River Basin, Alaska: Biological, Geographical, And Hydrological Research Of The U.S. Geological Survey Alaska Science Center

To address the need for understanding past, present, and future conditions in the northern latitudes, the United States Geological Survey's (USGS) Alaska Science Center conducts extensive research in the Yukon River Basin. The basin originates in Canada and spans Alaska from east to west encompassing diverse landscapes in the Arctic and sub-Arctic. Within this large watershed, USGS research is focused on understanding the rapidly changing conditions in the land cover and fires, fish and wildlife populations, and the hydrologic cycle. Some of Alaska largest and most extensive fires occur in the Yukon River Basin. Research suggests that recent fire frequency outpaces the forest replenishment. To provide a more thorough assessment of current fires, and prediction of future fire threats, Landsat imagery with its 30-m spatial resolution and 30-year history allow for unprecedented analysis of historical and existing landscape cover, the effects of fire and climate change on lake drying, and updating of fire burn boundaries. Additionally, caribou have been shown to avoid burned areas for at least 60 years because forage lichens were eliminated and preferred forage may require over 100 years to reach pre-fire abundance. Glaciers in Alaska and in Canada feed the Tanana River, a major tributary to the Yukon River. Gulkana Glacier is one such glacier where the USGS has measured the mass balance continuously since 1966. There has been a cumulative mass loss of more than 15 meters water equivalent since 1966, with two-thirds of that loss occurring since 1990. Streamflow statistics from long-term gaging stations show a tendency for earlier ice break up in the spring and earlier snowmelt peak flows. Glacier-fed streams show higher summer flows as warmer temperatures increased glacier melt. To provide a better understanding of the factors that regulate salmon production, USGS has examined the characteristics of chum salmon spawning habitats and survival of juvenile salmon at two locations within the Yukon River basin. Spawning sites characterized by up-welling ground water and stable water temperatures are used by chum salmon in Upper Yukon River tributaries where spawning may occur as late as November. In lower Yukon River tributaries, earlier spawning salmon use down-welling sites where water temperatures may vary between 0 and 13 ºC. The Yukon River delta is an internationally important breeding area for many waterfowl. Long-term studies of geese have recorded shifts in breeding phenology that are likely climate linked. Frequency and magnitude of storm surges may play a pivotal role in population dynamics of most breeding birds by indirectly mediating predation of nests. The hypothesis underpinning current research is that large storm surges decimate populations of tundra voles, which are the primary prey of arctic foxes. In the absence of voles, foxes increase predation of bird nests. Avian nest success this decade has been substantially lower than in the 1990s.