Although riparian forest buffers are often designed primarily for water quality benefits, these practices can also include woody species that provide products such as nuts, fruit, and decorative woody florals. (Source: USDA National Agroforestry Center illustration)

Many farmers use strips of native vegetation planted along streambanks, called riparian buffers, to reduce erosion and prevent agro-chemicals from entering watersheds. But less is known about saturated riparian buffers strips (SRBS), which, combined with patches of native plants, use a perforated pipe that redirects drainage water into the soil where roots and microbes can use the nutrients that would otherwise flow into surface water.

Loulou Dickey at Iowa State University said her research found that SRBS can be installed in more places than current guidelines suggest with little to no ecological harm.

Because water that runs off of farmland and into rivers and streams is one of the leading causes of water pollution in the United States, farmers and researchers are concerned with how to reduce this type of pollution.

“Limiting nutrient transport off of fields and into water bodies prevents overgrowth of harmful algae and protects in-stream ecosystems,” said Dickey.

Agricultural runoff occurs when excess nutrients are washed into waterways, where they accumulate, polluting aquatic ecosystems. These nutrients are good for crop health, but when they concentrate in bodies of water, they can become powerful pollutants.

Nitrogen fertilizers, for example, feed communities of algae downstream, creating blooms, or an overabundance of algae, that choke out aquatic life by absorbing oxygen. But SRBS can pull excess nutrients out of drainage water before they enter rivers and streams. SRBS can remove up to 92% of nitrate, a form of nitrogen, from agricultural runoff. 

Researchers tested riparian buffers, like this one, while also modeling hundreds of other realistic scenarios. The combination of real-world data and hundreds of simulations helped them assess where the buffers could be safely installed. The research found that more farmland can safely install riparian buffers – protecting more waterways. (Photo by Loulou Dickey)

This is good news for farmers and their downstream neighbors. Those living downstream of SRBS reap the benefits of reduced water pollution, including cleaner drinking water and better opportunities for fishing and other recreation. 

Riparian buffers create more benefits than just pollution reduction, however. Because perennial plant roots protect the streambank by holding soil in place, riparian buffers can reduce flood risk by slowing water velocity and preventing debris from damaging crops. They also tend to increase the presence of pollinators, which are vital to the health of many crops. SRBS have an added advantage because of their ability to redirect more drainage water to root zones, where increased nutrient uptake can occur.

SRBS can be inserted in a variety of sites, but existing USDA – NRCS guidelines limit installations, citing concerns about the impact on stream bank erosion.

But Dickey’s work suggests that these saturated buffers can be installed in more places than previously thought, with little to no increase in erosion. In her study, stream bank stability was affected by SRBS only 3% of the time. Increased erosion only occurred on sites with already unstable soils and among strips that were less than six feet wide, conditions that are not likely to occur in the field. The most effective buffer strips were at least 6.5 feet wide, which is well above the necessary width to prevent erosion. Dickey also found bank steepness was a better predictor of future erosion than the height of the bank. 

A solar-powered data logger measures water levels at an experimental saturated riparian buffer. It was installed by an Iowa State research team. (Photo by Loulou Dickey)

Farmers and landowners interested in installing saturated riparian buffer strips can tap a variety of state and federal funding that offers technical and financial support. 

“I hope our work will give farmers and landowners the confidence to install more saturated riparian buffer strips,”  Dickey said. 

Loulou Dickey’s research was supported by an Iowa NRCS grant under the USDA and in part by the National Science Foundation. 

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