Playa Sedimentation: Causes and Fixes

 

Playas are effective vectors for groundwater recharge and water filtration, but that assumes they’re in a healthy state. We can keep playas vital and functional by diverting topsoil runoff. Plant buffers around playas keep topsoil from clogging playas, and buffers filter chemicals from entering the groundwater.

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This is Playa Country — a weekly look at the wildlife, wetlands and prairies of the western Great Plains, and the people who manage them — brought to you by Playa Lakes Joint Venture, an organization dedicated to conserving birds and bird habitat.

The topic is care and maintenance of playas and rainwater basins, those temporary lakes — those “mud holes” or “buffalo wallows” as our grandads used to call them. We used to think nothing of those ol’ mud holes except how we’d need to clean up our boots after fixing fence through them. Well there’s been a bunch of research done on those things the past few decades, and it turns out they’re important to the landscape and our way of life. Scientists say playas are a primary method of groundwater recharge.

“When these playas dry out you get deep, large cracks in the floor of the playa wetland.” You’re hearing Ted LaGrange of Lincoln. He’s wetland program manager for Nebraska Game and Parks Commission. “And so when rainfall or snow melt enter that wetland, it goes down through those deep cracks and works its way eventually into the groundwater, recharging that aquifer.”

Turns out playa lakes, by definition, have a floor of clay. When dry, there are those deep cracks. When wet, the clay becomes impermeable to water, giving us these temporary lakes that are so good for the wildlife. But things happen to decrease the effectiveness of that clay pan from doing its job. Listen to Bill Johnson. He’s a biologist with US Fish and Wildlife at Canyon, Texas.

“When you have soils erode into the playa lakes, the volume of water that the playa can hold is then much shallower. That water is then spread out over a much bigger surface area, but it’s shallower, so it evaporates quicker. What you have is a playa that ultimately doesn’t hold as much water; it has a much shorter hydroperiod. And then it’s not as valuable to wetland wildlife; it doesn’t have as much plant production.”

When playas are situated on land that’s under production, it’s inevitable topsoil is going to run off.

“Playas are at the bottom of a hill, so in all directions around a playa the land goes upward. If there isn’t cover on that all the time, in the form of a grass or prairie cover, when you get heavy rains, you get erosion washing the plow-tilled soils downhill into the playa. One of the biggest threats to playas in general is sedimentation from farming.”

Playas on rangeland, says Johnson, are far more protected from siltation.

“Even with heavy grazing pressure, there’s at least plant roots in the soil holding the upland soils to the best they can where they belong, but when it is being farmed, the crops and their roots are only in the ground for a period of time, and the rest of the year the ground is typically fallow, or it’s recently plowed, so it is highly susceptible to erosion.”

So you have one of these playas smack-dab in the middle of a field. What can you do to prevent that siltation? Ted LaGrange says you install a plant buffer.

“That is a fringe of grassland around the wetland that can slow down that water and remove any of the issues of concern — whether it be sediments, pesticides, fertilizer — those types of contaminants can be removed by those buffers. So again, the first thing you want to do is to try to eliminate as much of that as you can, even before it gets to the edge of the playa, but if it’s flowing in that water and reaching the edge, you want to try to remove as much with a buffer as you can.”

So not only do these buffers consisting of grasses and forbs help keep silt out, they also filter herbicides and pesticides from entering the groundwater.

We can keep playas vital and functional by diverting topsoil runoff. Plant buffers around playas can keep topsoil from clogging playas, and the buffers filter chemicals from entering the groundwater. USDA’s Conservation programs can provide landowners and producers cost-share funds to help restore playas.

You’ve been listening to Playa Country, a weekly show about the wildlife, people and landscapes of the western Great Plains. This program is made possible by the Playa Lakes and Rainwater Basin Joint Ventures, and Enel Green Power.

Original broadcast: October 2012

Posted: April 5, 2015
Topics: Playas