Heterogeneity in High Latitude Lake Area Trends and Relationship to Landscape Characteristics

During the past ~60 years, net declines in lake area have been identified in several circumpolar regions. Lakes and wetlands in Alaskan National Wildlife Refuges (NWRs) provide critical breeding habitats for migratory waterfowl and shorebirds. The loss of these breeding habitats may have far-reaching effects along migratory routes that extend to more southerly parts of North America, South America, Asia, and Australia. However, the magnitude, mechanisms, and biological implications of lake area change have not been fully evaluated across Alaskan refuge lands. The objectives of this work were to: 1) use historical aerial photography and remotely sensed imagery to estimate lake area trends for 8 Alaskan NWRs at two spatial scales; broad-scale estimates were obtained for 10 study areas, and fine-scale estimates were obtained for ~24,000 lakes in these study areas, 2) characterize local to regional heterogeneity in lake area trends, 3) relate heterogeneous lake area trends to landscape characteristics and associated mechanistic processes, and 4) build empirical models to understand the potential effects of changing lake area on waterfowl species richness. Net statewide trends were decreasing (-0.73% per year). However, there was heterogeneity in rates of change among individual lakes (26.2% to -34.1% per year) and among study areas (0.3 to -3.0% per year) since ~1985. The lack of a latitudinal (Arctic to sub-Arctic) or longitudinal (continental to maritime) pattern in study area trends suggested the involvement of substrate characteristics and landscape position, rather than regional climatic gradients, as mechanisms underlying heterogeneous lake area trends. Study areas with a greater proportion of lakes outside of the immediate floodplain zone (> ~1.8 km from rivers), but still in lowland areas with coarse-grained soils were most likely to have net declining trends in lake area. These results indicated drainage and negative hydraulic gradients between surface and subsurface groundwater systems as important processes involved in declining lake area. These processes would be expected to lead to an increase in groundwater, a deepening of subsurface flow paths, longer hydraulic residence time, and increased soil respiration and CO2 release to the atmosphere. Within study areas, individual lake trends were heterogeneous but were also spatially clustered at relatively small (3-22 km) spatial scales. Fine-scale heterogeneity in lake area trends may be an important source of broad-scale system resiliency. Clusters of stable and increasing lakes may provide alternative habitat for species displaced from clusters of drying lakes.Large lakes (> ~100 hectares) tended to be more stable in area and also had a greater waterfowl species richness compared to smaller lakes. Because large lakes may be hotspots of biodiversity, their persistence may serve as potential centers of resiliency in these dynamic wetlands.