Sunday, November 16, 2014

The Playa Lakes of the South Plains

The geological region that Lubbock occupies is the Llano Estacado, or "staked plain." Forming the southern end of the Great Plains region of the central US, the Llano Estacado is essentially a massive mesa that stretches 250 miles north to south, and 150 miles east to west, covering much of northwest Texas and eastern New Mexico. The first Europeans to see this region were the members of the expedition of 1541 led by the Spanish explored Francisco Vasquez de Coronado. One of the members of the party described the flatness of the Llano, noting that there was not "a hill nor a hillock which was three times as high as a man." That same chronicler, Pedro de Castaneda, went on to describe one of the most distinctive geological features of the Llano Estacado:
Several lakes were found at intervals; they were round as plates, a stone's throw or more across, some fresh and some salt. The grass grows tall near these lakes; away from them it is very short, a span or less.
 Coronado called these small lakes playa lakes, because some of them had sandy shores and playa is the Spanish word for "beach."

Playa lakes are defined as shallow, roughly circular wetlands that are filled primarily by rainwater. They are small, usually around 15-30 acres, although a few can measure up to 800 acres. Playa lakes can be found in several states, including Oklahoma, Kansas, Colorado, and elsewhere, but they are most common on the Llano Estacado. About 85 percent of the playa lakes are in northwest Texas and eastern New Mexico.

Because they are filled by rainwater, playa lakes go through unpredictable wet and dry cycles. During dry peiods, the lakes can dry up completely, leaving only shallow depressions in the landscape. But a heavy thunderstorm can cause the lakes to fill quickly.

An Ecological Resource

Playa lakes are a valuable ecological resource. As noted in the quote above, the vegetation in the areas around the lakes is more lush than on the surrounding plains. Smartweed, millets, and other plants grow in abundance, and the wetlands support a variety of invertabrates such as tadpole shrimp. This makes the playa lakes region important stopover for migrating birds, especially water birds. In the fall and winter, an amazing variety of ducks, geese, cranes, shore birds, and wading birds can be seen on and around the playa lakes, especially in years of heavier rainfall.

During times of drought, when the play lakes dry up, and in cold winter periods when the lakes freeze over, migrating birds are forced to find larger lakes, reservoirs, and rivers. This can mean traveling long distances in a region where large sources of water are few and far between. If global climate change continues to produce severe and extended drought such as has occured the past few years, the consequences for birds migrating along the central flyway that passes over the Llano Estacado could be severe.

I took this photograph this morning of the playa lake in Clapp Park, near our house in Lubbock. Although it is still a bit early in the migration season, you can see a number of migratory waterfowl on the lake. Later in the fall and winter, many of the lakes around town will be covered with Canada geese and other waterfowl.

The ecological importance of playa lakes goes beyond providing a source of food and water for birds and other wildlife. These lakes play an important role in recharging the Ogallala aquifer. The Ogallala aquifer is a shallow underground layer of permeable rock that contains fresh water, stretching from South Dakota to western Texas. Lubbock sits above the southern part of the aquifer. In recent times, the Ogallala aquifer has provided a vital source of water for the communities of the high plains, and for crop irrigation. Because of the nature of the soil in the plains region, playa lakes are among the few places where groundwater can seep through to recharge the aquifer. It has been estimated that in the southern part of the Ogallala region, playa lakes are responsible for up to 95 percent of aquifer recharge.

Unfortunately, erosion and sedimentation caused by poor farming and grazing practices has seriously degraded many of the playa lakes, leaving them unable to collect and filter water to the aquifer. Establishing native prairie grassland buffers around playa lakes could help maintain the integrity of the lakes, reducing erosion and sedimentation, allowing them to collect water and filter it to the aquifer, while continuing to provide habitat for birds and other wildlife.

Playa Lakes in Lubbock

There are numerous playa lakes located within the Lubbock city limits. Over the years, the city has established parks around most of these lakes. The Texas Parks and Wildlife Department regularly stocks these lakes with catfish, bass, and trout for recreational fishing.

Clapp Park, which I pictured above, is one of the larger city parks and is in the neighborhood where I grew up. When we moved back to Lubbock two years ago, I was surprised to learn that this park, with its playa lake, is one of the best places in the area for bird watching, especially during the migrations in the fall and spring.

Another Lubbock playa lake at Leroy Elmore Park

Within the city, the storm sewer system channels rainwater into the playa lakes. This means that some of these lakes may retain water longer than normal even during dry periods. Nevertheless, I can remember many times during my life that the lake in Clapp Park went completely empty. I can even remember as a child walking across the dry, cracked lake bed, engulfed by the smell of rotting fish. The sight of a dry playa lake bed is, of course, part of the normal cycle of wet and dry for the Llano Estacado. Sadly, however, if recent trends of extended drought continue, this may continue to become a more frequent sight for this region.

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