Hydrogeologic Controls on Water Dynamics in a Discontinuous Permafrost, Lake-Rich Landscape

Abstract:

Understanding permafrost distribution, rate of change, and influence on groundwater movement are critical for assessing climate change impacts in northern ecosystems. Lake-rich lowlands in interior Alaska provide important habitat for migratory waterfowl, ungulates, and other wildlife. Despite low annual precipitation, the Yukon Flats area in the north central Yukon River Basin of Alaska (USA) supports over 20,000 lakes, due in part to the presence of permafrost. The fate of this lake-rich lowland and, by proxy, similar circumboreal lowland systems under projected climate warming is the focus of a series of recent studies highlighted here. Lake water chemistry analyses of over 200 lakes in the Yukon Flats reveal a large degree of spatial heterogeneity suggestive of a hydrologically disconnected system, a conclusion also supported by abrupt spatial changes in lake elevation. Airborne geophysical characterization shows a laterally continuous shallow gravel layer (~25-m thick) that would offer good hydraulic connectivity throughout the lowlands. However, the gravel layer is generally frozen (as permafrost) except beneath surface water bodies; thus inhibiting lateral pathways of groundwater flow under current conditions. Ground-based geophysical characterization provides a high resolution of permafrost distribution and relevant hydrogeologic features at several lake study sites. Relatively recent thaw in the gravel layer appears to be associated with lakes that have experienced change in size (area) over the past several decades, whereas lakes with taliks (unfrozen conduits) that fully penetrate the permafrost layer are more likely to be stable. Multi-scale permafrost characterization provides the basis for numerical models that simulate permafrost dynamics, lake-talik evolution, supra-, intra-, and sub-permafrost groundwater flow, lake-groundwater exchange, active layer dynamics, and permafrost aggradation response to lake recession. Collective field and simulation results provide insight into expected alterations in groundwater flowpaths, water budgets, lake distribution, and lake chemistry in discontinuous permafrost lowlands given continued climate and permafrost change.