• Glacier contribution to lowland streamflow: a multi-year, geochemical hydrograph separation study in sub-Arctic Alaska

      Gatesman, Tiffany A.; Trainor, Thomas P.; Liljedahl, Anna K.; Douglas, Thomas A. (2017-12)
      Glacier melt affects the geochemical composition of rivers; however, quantifying the glacier contribution to subarctic watershed-scale runoff has attracted limited attention. To estimate glacier contribution, we conducted a 6-year geochemical hydrograph separation study in a geologically heterogeneous glacierized watershed in Interior Alaska. Water samples were collected daily from Jarvis Creek during late April through September. Source waters were collected synoptically each year from rain, snow, baseflow (winter discharge), and the glacier terminus discharge. All samples were analyzed for stable water isotopes and dissolved ion concentrations. Stream surface water samples have large seasonal and inter-annual geochemical variation, however, source waters show distinct chemical signatures allowing the application of a geochemical hydrograph separation model to quantify relative source contribution to lowland streamflow. Considerable inter-annual differences within source water signatures emphasize the importance in informing the model with source waters sampled for each season. We estimated a seasonal average of 35% (20 to 44%) glacier terminus discharge contribution with a daily range of 2 (May) to 80% (September). If glacier contribution was to cease completely, stream discharge would be reduced by 48% and 22% in low and high rainfall summers, respectively. Combined with the documented shrinkage of glaciers, our findings emphasizes the need for further research on glacial wastage effect on subarctic watersheds.
    • Shrinking boreal lakes as agents of change: untangling structure and function in hydrologically-coupled lakes and wetlands

      Patil, Vijay P.; Griffith, Brad; Euskirchen, Eugenie; Waldrop, Mark; McGuire, A. David (2018-05)
      Widespread lake shrinkage has occurred over the last 30 years throughout interior Alaska and other boreal regions. This trend has been broadly linked to climate change, via multiple proximate drivers including permafrost thaw, shifting water balance, and terrestrialization caused by peat growth. The ecological effects of shrinking boreal lakes are still poorly understood. I used space-for-time substitution based on field surveys from a spatially balanced random sample of lakes (n=130) to examine the implications of shrinking lakes in the lowland floodplain of the Yukon River within the Yukon Flats National Wildlife Refuge in northern Alaska. Historical lake shrinkage over the last 30 years increased plant functional diversity, woodiness and aboveground biomass in lake-margin wetlands, despite a significant loss of wetland and lake area. Shrinking lakes appeared to have decreased hydrological connectivity with surrounding wetlands, and reduced organic carbon and nitrogen inputs from the surrounding landscape. However, land cover and bathymetry were better predictors of water chemistry than lake shrinkage. Continued reductions in lake surface area, combined with terrestrial succession, may reduce wetland area and increase the relative abundance of woody wetland vegetation compared to herbaceous plants. Lake shrinkage could also reduce below-ground C stocks, because lake sediments contain more organic C per m² than terrestrial soils, and lake sediment C appears vulnerable to aerobic decomposition. Overall, lake shrinkage will most likely affect plant and animal biodiversity, waterfowl and wildlife habitat quality, and C storage in contrasting ways, and management of drying landscapes may require difficult tradeoffs to be made as a result. These decisions would be aided by process-based modeling that accounts for the role of plant functional traits and explicitly represents hydrological interaction between terrestrial and freshwater ecosystems.