Photo: Wood Duck
"The Wood Duck is one of the most stunningly pretty of all waterfowl." Learn more about this and other birds at The Cornell Lab of Ornithology All About Birds website. Photo courtesy of Tom Grey.
Wet or Dry, Playas Are Productive
One might think that a dry playa doesn't have much to offer nature — or people, for that matter. It seems only logical that a wetland is at its best when it is wet. But the truth is that playas require periods of drying out for proper function. It is simply the nature of playas to go through these periodic wet and dry cycles — and is what makes them such an ecological asset.
Playas are the primary source of recharge for the Ogallala, contributing up to 95 percent of the overall return of water to the aquifer. During dry periods, cracks that are essential for aquifer recharge form in the clay bottom. When this layer dries, it develops deep cracks and fissures, which are channels for recharge. If playas never dried out, recharge to the Ogallala Aquifer would be significantly compromised.
Current research indicates that most recharge through playas happens during the first big rainfall as water drains through the cracks in the playa floor. As the rain continues, the clay layer becomes saturated and expands, cracks close, and the basin forms a seal to hold water, thus slowing recharge. Once these cracks are sealed, recharge is primarily limited to the playa perimeter where the clay layer meets upland soil.
If playas were wet all the time, some plants that require periods of flooding and drying to germinate would not grow at all. Tiny life forms — water fleas, fairy shrimp, and tadpole shrimp — can also be found in playas. The soil can be dry for months or years, but it is full of life nevertheless. Invertebrates aren't the only life to be found in a dry playa; amphibians, as well, can lie dormant in dry playa basins for several years, taking refuge until the next storm hits the playa.
Sedimentation — the number one threat to playas — can impact playas' water holding capacity. It reduces the amount of water a playa can hold, and spreads it out to a larger surface area, increasing water loss by evaporation. Sedimentation occurs through two processes. Sediment can be washed into the playa during large rain events or it may be introduced into a playa if it is plowed for crop production. Eventually, sediments fill playa basins, causing playas to lose most of their wetland function and become 'fossil playas.'
Given the region's dependence on the aquifer for farm and municipal water, and the drastic decline in the water table over the past century, maintaining the natural functions and cycles of playas is crucial for sustaining the economies and communities of the western Great Plains.