Thermokarst Lake Drainage - Vulnerability to Climate Change and Prediction of Future Lake Habitat Distribution on the North Slope

Lakes of the Arctic Coastal Plain of northern Alaska provide essential habitat for many species of water birds and fish, but are vulnerable to the effects of climate change. The mechanisms of effect include interactions between climate, permafrost, and surface hydrology that are reasonably well understood, but managers need a spatially-explicit model of landscape change to assess the risk of lost habitat value. Mean annual air temperature in Arctic Alaska is projected to increase 7°C by the end of the century. In a zone of deep, continuous permafrost, warming temperatures influence permafrost in ways that both promote and jeopardize the persistence of large lakes. Warming results in accelerated thermal erosion of lake shores and expansion of deep lakes at the expense of adjacent tundra habitats In general, therefore, large deep lakes in the Arctic Coastal Plain and Foothills ecoregions are likely to increase in area. In some landscapes, however, lakes will be susceptible to catastrophic drainage, as lakes are “tapped” by new drainage networks resulting from permafrost degradation. The vulnerability of an individual lake to tapping is dependent on the ice-content of surrounding permafrost and the existence of a topographic gradient. Ongoing remote sensing research by the PIs found numerous thermokarst lakes on the North Slope and the Seward Peninsula that drained during the last 50 years. Drainage rates on the North Slope, in cold continuous permafrost, were found to be 1-2 lakes / year. On the northern Seward Peninsula, a warm continuous permafrost region near the boundary to discontinuous permafrost and a potential analogue for future North Slope conditions, up to 10 lakes / year were draining. These drainage events appear to be connected to surface permafrost thawing, tapping by ocean coastal erosion and river channel migration, lake expansion, human-caused disturbances, and other factors. Thermokarst lake drainage completely changes the habitat character of a site. The Arctic Coastal Plain contains the second-largest lake district in the state, providing essential breeding, molting, and migratory stopover habitat for millions of migratory water birds, including 3 species of loons, and 20 species of large waterfowl (ducks, geese, and swans). Notable among these species are the Yellow-billed Loon, which is currently a candidate for listing under the Endangered Species Act, and Spectacled and Steller’s eiders, both listed as “threatened.” North Slope lakes also provide habitat for a variety of resident and anadromous fish, including least cisco, round whitefish, broad whitefish, lake trout, arctic char, arctic grayling, and ninespine stickleback. Lakes that are connected to stream systems are particularly important, as are deep lakes (> 2 m) that provide overwintering habitat. Understanding the potential for loss of lake habitat is vital to assessing the vulnerability of water birds and fish to range contraction and/or population decline.