When Arctic Lakes Drain: Plants and Permafrost Move In

Early in the summers of 2018 and 2019, four lakes on the northern coastal plain of Bering Land Bridge National Preserve in Alaska — each larger than 100 hectares — drained away. They were part of an alarming loss of lakes there over the first two decades of this century. The drainages were probably triggered by record warm weather from 2014 to 2019 and above-normal snowfall in 2018–2019. Scientists with the Park Service's Arctic Inventory and Monitoring Network set out to watch what grew back.

The four study lakes (in yellow) in Bering Land Bridge National Preserve that drained in 2018–2019. Credit: National Park Service.

What grew back

• Fast colonization. The moist, loamy lake-bottom mud was colonized quickly. In one lake, plants covered most of the former bottom by the end of the summer it drained; the others filled in over the next two summers.
• Pioneers first. The first plant communities were dominated by just one or two species that grew, but were not abundant, in the surrounding tundra. Some probably sprouted from seeds stored in the mud; horsetail (Equisetum) probably grew from spores that blew in soon after drainage.
• Lush by year three. By the third summer, most areas held diverse, lush stands of tall wetland grasses and sedges.
• Permafrost returns. By 2021, two or three years after drainage, permafrost was forming in the lake bottoms, and some plants that dominate the region's old drained lakes had appeared.

In the first year or two, one or two species dominated (top); by the third summer, tall wetland grasses and sedges had taken over most areas. Credit: National Park Service.

The new basins seem to be heading toward what old drained basins nearby look like — permafrost, acidic peaty soils, and sphagnum moss and sedges — though that transition is likely to take centuries.

What it means for loons

Losing 2% of yellow-billed loon habitat in just two years could add up if lakes keep draining; red-throated loons don't appear threatened.

How the monitoring works

Scientists sampled vegetation in 2019 and 2021 and installed 16 permanent plots in the basins of the lakes that drained in 2018–2019, plus 30 more in basins elsewhere in the network that drained before any historical records or aerial photographs. They repeatedly measure each plant species' cover and the depth to frozen ground, and use satellite images to see when lakes drained, how fast plants came back and where different communities grow.

So far, the basins are following the historical pattern. With the climate warming, they will keep watching to see whether that changes.

Sources

Based on "Vegetation and Permafrost Return to Drained Lake Basins," Terrestrial Vegetation Monitoring Brief, 2022, National Park Service Arctic Inventory and Monitoring Network; a work of the United States government in the public domain. The full Natural Resources Report on drained-lake vegetation and loon habitat is on the NPS DataStore.