Lakes and wetlands in Alaskan National Wildlife Refuges (NWRs) provide habitat diversity in boreal forests and critical breeding habitats for millions of migratory waterfowl and shorebirds in North America. Widespread reports of lake drying in the current warming climate suggest that breeding habitats may decline. Any loss of these breeding habitats may have local effects on biodiversity and on subsistence and sport hunting economies as well as far-reaching effects along migratory routes that extend to more southerly parts of North America, South America, Asia, and Australia. In 2006, the Alaska Cooperative Fish & Wildlife Research Unit began a research program to investigate the magnitude, mechanisms, and biological implications of lake drying in Alaskan refuges. Three research objectives have been met, while work is in progress to meet the other two study objectives.

The objectives of the study were to:

1. Use aerial photography and satellite imagery to estimate trends in lake size in eight Alaskan NWRs at multiple spatial scales ranging from individual lakes to major portions of refuges,
2. Characterize the lake-to-lake and refuge-to-refuge variability in lake size trends,
3. Identify mechanisms associated with trends in lake size,
4. Establish relationships between lake characteristics and waterfowl species richness, and
5. Use estimates of lake size trends and lake characteristics to project the potential effects of changing lake size on waterfowl species richness.

Statewide, net trends in lake size were decreasing at a rate of -0.73 percent per year. However, there was substantial variability in rates of change among individual lakes (26.2 percent to -34.1 percent per year) and among average rates of change within refuges (0.3 to -3.0 percent per year) since about 1985. One-half of refuges had significant declining trends and, if these trends continue, these refuges could lose 30-80 percent of their lake area within 50 years. Rates of increase in lake size for the remaining half of the refuges were not sufficient to counteract these substantial drying losses.

The lack of a latitudinal (Arctic to sub-Arctic) or longitudinal (continental to maritime) pattern in study area trends suggested the involvement of local landscape characteristics rather than regional climatic gradients as primary mechanisms driving spatial variability in lake size trends. Shrinking lakes had wider floating mats of vegetation, were on coarse-grained soils, were within areas that had burned within the past 50 years, and were farther from rivers than lakes that were increasing in size. These results implicated permafrost degradation and frequency of recharge as important mechanisms involved in declining lake size. These mechanisms may lead to an increase in soil respiration on newly exposed lake bottoms including CO₂ release to the atmosphere and could provide a positive feedback to climate warming.

Preliminary results show that waterfowl species richness is positively related to lake size, maximum lake size within 3 miles, as well as the proportion of the lake perimeter occupied by wetlands, and negatively related to distance from rivers. Using individual lake trend estimates derived to date, we will use this model of species richness to project the future species richness at lakes within refuges assuming current trends continue.

To date, this project has provided baseline data on lake size trends for approximately 23,000 lakes within Alaska, and an efficient methodology for continuing to monitor lake trends and maps of current waterfowl species richness. By quantifying relationships between statewide coarse resolution maps of landscape characteristics and spatially variable responses of lakes to environmental change, a means to identify at-risk lakes and landscapes and plan for a changing climate is provided. These products may be used to inform land exchange decisions, identify potential changes in traditional subsistence hunting areas, and identify lakes and study plots that may be employed to conduct fine scale investigations of the effects of lake trends on biological processes.

Each month, the ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new wildlife research projects that we believe our readers will appreciate reading about.