Arctic landscapes are undergoing rapid changes due to climate warming at high latitudes. As air temperatures warm, the boreal forest is expanding north into tundra, and permafrost soils are thawing. These shifts in terrestrial ecosystems can dramatically alter what happens in aquatic ecosystems. In a new study published in Environmental Research Letters, researchers from the U.S. Geological Survey, the University of Alaska Anchorage, and the National Park Service show that streamflow may be declining in headwater reaches due to the combined effects of vegetation change and permafrost thaw.
In this collaborative study, scientists examined hydrological conditions across 11 headwater catchments in Noatak National Preserve and Kobuk Valley National Park in northwest Alaska. Study catchments varied with the amount of forest cover and the degree of permafrost thaw. They used this gradient in vegetation and permafrost to explore how these factors might control streamflow. Findings from this study suggest that there are two main processes contributing to lower streamflow in headwater reaches. First, boreal tree line expansion causes an increase in evapotranspiration, or the physical and biological transport of water to the atmosphere. Second, permafrost thaw reroutes water to deep groundwater aquifers, often bypassing the stream channel. Together, these processes can cause streamflow to decline and may contribute channel drying. Headwater streams serve as critical habitat for native fish species in the Arctic and this decline in flow may contribute to a loss of habitat.
Source: U.S. Department of the Interior, National Park Service