Playas

Wet or Dry, Playas Are Just Plain Productive

One might think that a dry playa doesn't have much to offer for nature — or people, for that matter. It is a perfectly excusable assumption that a wetland is at its best when it is, well, wet. But the truth is that playas require periods of drying out to produce food for wildlife and recharge the Ogallala Aquifer. It is simply the nature of playas to go through these seasonal wet and dry cycles, and what makes them the most thriving ecological assets of the Southern High Plains and Western Great Plains. Here are some reasons why:

Dry Playas are Refuges for Life

The next time you are out on a dry playa, scoop some soil from the basin and put it in a sealed glass jar. Take it home add some water. In a few weeks, tiny life forms — water fleas, fairy shrimp, and tadpole shrimp — will begin to appear. The playa soil you collected could have been dry for months or years. But it is full of life nevertheless.

Playas are refuges for a diverse mix of invertebrate and plant species that would otherwise cease to exist if a playa was wet all the time. Some of wetland birds’ favorite foods — smartweed, toads and other treats — depend on the wet/dry cycle of playas for their survival.

If a playa were wet all the time, some of these species — like smartweed which requires periods of flooding and drying to germinate — would not grow at all. While others — like spadefoot toads — would be eaten up by predators before they had the chance to reproduce enough to sustain their population. Toads can lie dormant in dry playa basins for several years, basically taking refuge until the next storm hits the playa.

"In some of the playas that we sample that have been dry for a couple of years, amphibians show up as soon as it starts raining. It’s amazing," commented renowned playa researcher Dr. Loren Smith. You can hear more about Smith’s research on and observations of toads on playas on Playa Country Radio.

The length of time a playa is wet or dry — or a playa’s hydroperiod — is extremely important to maintaining its productivity.

"A playa has got to dry out to be productive, but you don’t want them drying too rapidly," Smith said. "If a playa dries out too quickly, amphibians, water fleas and other species can’t reproduce. Sooner or later that playa becomes a population sink."

Sedimentation — the number one threat to playas — can cause playas to dry out too quickly. Sedimentation occurs when rain or other runoff event carries loose soils into playa basins, gradually filling them. This happens especially on playas in cropland. Sedimentation reduces the amount of water a playa can hold, and spreads it out to a larger surface area which increases water loss by evaporation. Playa researchers estimate that more than 50 percent of all playas have been effectively “fossilized” by sedimentation and have lost most wetland functions.

Seasonal Wetlands Support More Ducks

Because of the seasonal flush of plants and inverts, playas and other temporary wetlands actually produce more food for birds and other wildlife than do permanent wetlands. According to PLJV biological modeling, a playa will produce 428 "duck-use-days" — or the amount of food needed to sustain a duck for one day — per acre as compared to 225 use-days provided by one acre of reservoir or freshwater lake. Even more productive are "moist-soil units", wherein a wetland is managed to create cyclical wet/dry conditions — which yield 4,223 DUDs per acre.

Dry Playas Set the Stage for Aquifer Recharge

Recharge to the Ogallala Aquifer would be significantly compromised if playas never dried out. Playa basins are lined with clay soil. When this layer dries, it develops deep cracks and fissures which are channels for recharge.

Current research on recharge indicates that most infiltration through playas happens when the wetland is first inundated with water. Once full of water, the clay layer expands, cracks close, and the basin forms a seal to hold water and recharge slows. Once these cracks are sealed, recharge is primarily limited to the playa perimeter where the clay layer meets upland soil.

Playas are the primary source of recharge for the Ogallala, contributing up to 95 percent of the overall return of water to the aquifer. 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 economies and communities of the High Plains.

Read more information on playas’ link to aquifer recharge.

~August 2007