Natural buffer zones can filter nitrates from groundwater

Nitrogen can be a tricky element to deal with for farmers. While it’s a popular and important ingredient in many fertilizers, it can also run off into nearby streams and seep into the groundwater as nitrates, which creates dead zones and algae blooms that kill fish.

Now, new research has identified nitrate removal hotspots where nitrates from fertilizers are filtered out of the water, usually by a buffer zone with local plant species.

Molly Welsh, a graduate student from the State University of New York College of Environmental Science and Forestry, led a study that found and analyzed these hotspots.

“Understanding where nitrate removal is highest can inform management of agricultural streams. This information can help us improve water quality more effectively,” said Welsh.

The researchers collected data and water samples from four streams in Northwestern Carolina, exhibiting a wide range of nitrate removal close to agricultural activity.

Welsh then analyzed the water samples and found that the buffer zones next to the streams had the highest success rate of nitrate removal. Sediments in the waterways, which were also analyzed, were not nearly as efficient at removing nitrates.

Buffer zones are abundant with organic matter, high levels of moisture, and fine-textured soils, which makes them perfect at filtering out harmful contaminants. Nitrate removal appears to highest where there is a lot of native plants and fine sediments.

Welsh also examined pools created during stream restoration using rocks that spanned across the waterway, which was also not very effective at removing nitrates.

Welsh suggests that using woody debris would be a better method than rocks to filter nitrates given the success of the buffer zones.

“Our results show that it may be possible to develop simple models to guide nitrogen management,” said Welsh.

The new research shows the importance of natural buffer zones to protect ecosystems from harmful nitrate runoff.

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By Kay Vandette, Earth.com Staff Writer