Exploring a Dried Lake Bed

By Bruce G. Marcot, Ecology Picture of the Week:

On this crisp summer day we are flying over the arid landscapes of the northern Sonoran Desert in southwestern Arizona.  From this airliner altitude, little vegetation seems to inhabit this land.  And the scene is dominated by two playa lakes.

Technically, a "playa" is a lowland desert basin that is undrained, and a "playa lake" is the shallow, ephemeral lake that forms in the wet season within the lowest parts of a playa.  Playa lakes dry during the summer and their evaporation sometimes leaves pans of salt deposits as well as dried streambed and drainage lines on the naked desert landscape.

So what's in the playa lakebed beside alluvium (sediment deposited by flowing water) and evaporative salt?  Playa lakes -- when wet -- can actually provide important habitat for a wide variety of migratory birds.  For example (Haukos and Smith 1992), in west Texas, some 20,000 playa lakes provide habitat for some 115 bird species including 20 species of waterfowl, and 10 mammal species.  Waterfowl nesting in the area produce up to a quarter million ducklings during wetter years. Over 400,000 sandhill cranes use these wetlands during their winter migration, and wintering waterfowl number one to three million birds. 

Playa lakes also host ephemeral populations of many invertebrate species including mayflies, dragonflies, grasshoppers, true bugs, beetles, flies, and many others, although the life histories and ecologies of many of these species are poorly studied or unknown.  Many of these invertebrates play key roles in food webs and energy webs of playa ecosystems, and feed millions of hungry ducks and other birds.  

But not all is happy in playaland.  Playas can concentrate wintering birds and instigate the ready spread of disease including avian cholera and botulism.

Studying ancient shorelines of playa lakes can also tell us a lot about historic and prehistoric changes in local climate.  

As harsh as this desert landscape appears, playa ecosystems can be very fragile, and their wetlands quite valuable to wildlife and farmers alike.  Conservation measures for playa lakes have focused on striking a balance on water use and providing protection of wetlands.

  --Bruce G. Marcot

Image and text © Bruce G. Marcot, Ph.D. Research Wildlife Ecologist,
who produces the Ecology Picture of the Week website.