New Study on Riparian Buffer Zones Yields Updated Information

A 12-year study by Deanna Osmond, soil scientist at North Carolina State University, and colleagues yielded updated information on the effectiveness of riparian buffers in removing excess nitrogen from agricultural runoff.

The excess nitrogen can enter surface waters with devastating consequences, like Algal blooms and fish kills. But riparian buffer zones—areas of grasses, perennials or trees—between farmlands and streams or rivers can help.

Riparian buffer zones can reduce pollution, provide habitat for wildlife, hold banks together, provide food for animals and dampen the flow of agricultural runoff, which can lead to lower amounts of nitrogen reaching streams and rivers.

The researchers also found that irrespective of vegetation type, wider buffer zones are more effective than narrower ones. It is important to consider the width of buffers. “There is a trade-off between productive farmlands and buffer zones,” Osmond said. Farmers cannot grow crops in buffer zones.

Previous studies had typically involved buffer zones measuring at least 30 meters wide. But this study involved buffers that were either 8 or 15 meters wide. Even narrower buffer zones lowered the amount of nitrogen reaching streams. The 15-meter wide buffers were often more than twice as efficient at removing nitrogen from runoff compared to the 8-meter buffers.

The researchers also studied the types of vegetation that make buffer zones most efficient at removing nitrogen from runoff. Their recent study showed that for some areas, it doesn't matter what kind of vegetation buffer zones are made up of. Previous studies found that certain vegetation types are more effective at nitrogen removal, but this is likely because of differences in soil conditions and stream flow. The majority of previous studies were in areas where streams are more connected to their floodplains, which leads to a higher groundwater table and thus the more efficient transformation of nitrates into nitrogen gas.

“Location matters when studying riparian buffer zones,” Osmond said.

This study was conducted in the upper coastal plains of North Carolina where the streams were not connected to their floodplains, which could have affected how efficiently the different vegetation types removed nitrogen from runoff.

Microbes also need carbon to eat and live. The process is most efficient when levels of dissolved organic carbon in the soil are high. At all the measurement sites in this study, the dissolved organic carbon levels were low, which may have limited the amount of nitrates being removed from runoff and equalized differences between different vegetation types.

Finally, while many studies measure the effectiveness of preexisting buffer zones, Osmond’s study “started from scratch.” This method more closely reflects the reality in many farms where buffer zones are not preexisting. Osmond's study also tracked the buffer zones for 12 years, far longer than most other studies. Studies in different regions can help us better understand the factors that affect nitrogen removal. 

“Many factors affect how efficiently riparian buffer zones remove nitrogen from runoff,” says Osmond.

Read more about Osmond’s study in the Journal of Environmental Quality.

Source: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America