EPOW - Ecology Picture of the Week

The Changing Arctic: Drained Lakes

Drained thermokarst lake
Bering Land Bridge National Park, Alaska USA

Explanation:  This week we are in extreme western Alaska out on the Seward Peninsula that, during the Pleistocene and the height of the last global glacial maximum, united Asia with North America across the Bering Strait.  Part of the Seward Peninsula has been designated a national park -- the appropriately-named Bering Land Bridge National Park, in fact.  

But it is here where we are seeing stark evidence of changes occurring again throughout the high Arctic.

In the main photo, above, we are viewing a thermokarst (ice-melt) lake that has nearly completely drained.  When the permafrost (frozen ground) below the "active layer" (seasonally-thawed surface) of the soil melts because of changing climate climate and increasing annual temperatures, such lakes can drain like bathtubs when the drain plug is removed.  What is left is a depression with residual ponds in the lowest sections.

The lake basins are then often deeply thawed, and rich and moist with organic sediments that support vigorous vegetation growth, as shown in the following photos and examples from the same area:
  

Another drained thermokarst lake with vegetation growing
vigorously from the organic-rich sediments.
See next photo.

In this color-enhanced version of the above photo, you can
more clearly see the various bands of vegetation ranging
from willow shrubs now growing into the drained lake basin,
to emergent aquatic vegetation in the remaining pond.

Whether there is a net loss, draining, and drying of lakes throughout the Arctic, as caused by increasing temperatures and melting of the permafrost layer, is currently being studied.  Regardless, so many tundra lakes in the region have apparently become drained due to permafrost melt and other dynamics, that it may be a concern for wildlife that depend on these ecosystems.    

  
Acknowledgments: 
My thanks to ecologist David K. Swanson of the National Park Service for his ongoing studies of vegetation and implications of climate change in the region, and for his help in interpreting the dynamics of lake drainage presented in these photos.