Interior Alaska's lakes, 2000 to 2019: mostly stable, but 9 of 32 areas lost surface water

Warm, wet spells coincide with bigger lakes in Alaska's interior, but over two decades the net result was a small but significant loss. National Park Service aquatic ecologists tracked surface water from 2000 to 2019 in three parklands. The work comes from the Central Alaska Network Shallow Lake Monitoring Program, which studies lakes and ponds in Denali National Park and Preserve, Wrangell-St. Elias National Park and Preserve and Yukon-Charley Rivers National Preserve.

Surface water content of the ecological areas studied in the three parklands, overlaid with Alaska climate regions. Image from the National Park Service's page.

What the data showed

Declines in lake area in Arctic and sub-Arctic Alaska have been linked to changing precipitation, permafrost degradation, higher evaporation and terrestrialization. The study used satellite-based tools, in particular the USGS Dynamic Surface Water Extent product, to test trends across 32 ecological areas. In all three parks surface water fluctuated in similar ways, probably following swings in regional climate, and the high periods coincided with relatively warm, wet spells. Surface water area fell in 9 of the 32 areas and rose in only one, a floodplain of the Copper River in Wrangell-St. Elias. The largest losses were in Denali.

Where lakes shrank and where they grew

Lakes most likely to lose area sat in glacial and thermokarst landscapes, meaning ice-rich permafrost, perpetually frozen soil, or buried glacial ice. Declines were largest in glaciated landscapes with coarse substrates and areas on ice-rich permafrost. In some places with ice-rich permafrost or buried glacial ice, lakes expanded as the frozen ground thawed. In such actively eroding areas, growth made up for losses, which made trends hard to see, and in several areas some lakes grew while others shrank, masking the change.

Lake margin expansion due to permafrost deterioration. NPS photo.

What it may mean

Climate models project more temperature and precipitation in Alaska, which would significantly degrade permafrost and glaciers in the parks. One consequence, more groundwater connectivity, could cause lakes to expand or drain depending on underground flow paths. The authors suggest that warm, wet periods, when permafrost and glaciers deteriorate most, may make the interior look wetter as melt and thaw feed surface water, and that if those features degrade, drying and surface-water loss are likely to be more common. Shallow lakes are critical habitat for wildlife, including many migratory birds, so losing them could affect important breeding populations. Because lake responses vary and sometimes conflict, the authors stress the need for long-term monitoring of interior lakes in varied settings.

Trends in lakes surveyed in Denali National Park and Preserve. Image from the National Park Service's page.

Trends in lakes surveyed in Wrangell-St. Elias National Park and Preserve. Image from the National Park Service's page.

Trends in lakes surveyed in Yukon-Charley Rivers National Preserve. Image from the National Park Service's page.

Sources

• National Park Service, "Lake Area Change in Interior Alaska Parklands", by aquatic ecologists Danielle Knapp and Amy Larsen, https://www.nps.gov/articles/000/lake-area-change.htm; based on D. L. Rupp and A. S. Larsen, "Surface water area in a changing climate: Differential responses of Alaska's subarctic lakes", PLOS Climate 1(6), 2022; rewritten in hubnx's own words.