There’s no question riparian buffers are good for the landscape.  Lining the banks of streams and rivers, these narrow bands of vegetation keep soil from washing into waterways, and help hold fertilizer nutrients on the fields as well.  They can even do the same trick for some pesticides – some, but not all.

That’s the finding from researchers at Penn State, who received a three-year, $750,000 USDA grant to study riparian buffers’ ability to reduce water pollution.

The researchers looked at two field-sprayed herbicides – atrazine and simazine – as well as four insecticides used as seed coatings – clothianidin, imidacloprid, thiacloprid and thiamethoxam.  This focus on particular pesticides is important, since each can move differently with surface and groundwater depending on its own specific chemistry.

The researchers tested five different streams in the same watershed for the presence of these pesticides.  The most commonly occurring were simazine (found in 93% of samples), atrazine (92%), and clothianidin (75%).

The higher the streamflow, the greater the concentration of atrazine and clothianidin, suggesting that these chemicals were moving in water flowing over the land surface.  As such, riparian buffers should be more effective at catching them and holding them out of streams.

By contrast, simazine’s concentration was more constant regardless of streamflow levels, meaning that it probably travels more through groundwater and would not be trapped by riparian buffers.

The study region has higher than usual groundwater flow rates due to its porous limestone “karst” geology.  Thus, these findings may not apply everywhere.  However, Oklahoma does have several areas of karst formations, including in the Arbuckle and Ozark mountains, as well as in the Limestone Hills in the southwestern part of the state.

“Our results here show that buffers are helpful, but only for pesticides that move in surface runoff – groundwater-transported pesticides, especially in karst watersheds, can bypass buffers entirely,” said lead researcher Heather Preisendanz.

“Before we choose how to reduce pesticide pollution, we need to consider how pesticides actually move through the landscape, because we can’t greatly reduce pesticide pollution with buffers alone if the pesticides are slipping underground.”

The study was published in the Journal of Environmental Quality.