A stream in autumn with trees and vegetation along both banks, with an old barn and agricultural fields in the background.
Trees and vegetation along a stream's banks help protect it from agricultural runoff. Credit: iStockPhoto.com/TimNewman

Agricultural land uses, including both crop and livestock production, are known to have myriad detrimental effects on streams and rivers. According to the EPA, agricultural runoff is a major source of surface water pollution—the excess nutrient runoff from fertilizer and livestock manure causes poor water quality and reduced habitat and biodiversity among animals living in both the waterways that directly receive agricultural runoff and those downstream. Wildlife aren’t the only ones affected by surface water pollution, of course—about 70% of the fresh water used in the United States comes from surface sources.

Landowners’ adoption of [conservation] practices is not yet widespread enough to adequately protect waterway ecosystems.

Over the years, researchers have identified a variety of conservation practices that can help mitigate agriculture’s effects on waterways, but landowners’ adoption of such practices is not yet widespread enough to adequately protect waterway ecosystems.

In the United States, the Clean Water Act has been used extensively to clean up water pollution that can be traced to specific point sources, such as pipes. But when it comes to addressing nonpoint source agricultural pollution that tends to be distributed across the landscape, “we don’t have the levers that we have for point [source] pollution in the Clean Water Act,” said Robert Hughes, an aquatic ecologist, past president of the American Fisheries Society, and author of a review published in Water. Indeed, most agricultural activities are exempt from Clean Water Act requirements.

Although the Clean Water Act is meant to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters,” doing so is not possible if agricultural pollution isn’t addressed. Hughes and Robert Vadas Jr., an aquatic ecologist and coauthor of the review, make a scientific case for increasing protection and rehabilitation of streams and rivers from agricultural pollution.

Reviewing Literature from 21 States

The authors reviewed 44 studies spanning 21 states that looked at the effects of implementing conservation practices on fish, stream insects, and birds, with about half of the case studies examining croplands and the other half focusing on rangelands. Although these studies varied in their designs and methods, the authors noted that in general, sites that took measures to keep agricultural effects farther away from waterways tended to show improvements in their biological health indicators.

For croplands, a major tool the studies used for stream protection was a riparian buffer, or a strip of land planted with permanent trees or vegetation along the banks. “Buffer zones can help on multiple fronts,” said Dana Infante, the interim director of the Institute of Water Research at Michigan State University and AgBioResearch assistant director for natural resources. “They can slow surface runoff that might be originating from upland areas that are converted to agriculture. They can help trap sediments or nutrients that runoff might be carrying.” She also noted that riparian buffers can improve stream habitats by providing shade to help keep the water cool, by adding food in the form of organic matter, and by contributing additional habitat when woody debris falls in.

In addition, a stream’s riparian zone “provides a hydraulic buffering—the floods will tend not to be as bad through areas that are better forested,” said Vadas. Hughes added that riparian buffers can “provide a highway, essentially, for many terrestrial animals—everything from insects to birds to mammals, they use those as passageways through the landscape.”

Despite all these benefits, many farmers are reluctant to adopt riparian buffers voluntarily. Tong Wang, an agricultural economist at South Dakota State University, attributes this largely to their cost, saying via email that in the farmers’ view, “buffer strips offer less on-site benefits, in terms of soil health improvement and long-term profit increase,” compared to cover crops. And these buffers can require costly maintenance. Pennsylvania State University agricultural engineering professor Heather Preisendanz explained that for landowners installing forested riparian buffers, the time and effort involved in getting the newly planted trees established in the buffers can be significant. This effort can lead to farmers scrapping the idea altogether.

Encouraging Solutions Through Policy

In Pennsylvania, buffer strip adoption has become more commonplace thanks to the state’s participation in the Chesapeake Bay Total Maximum Daily Load (TMDL). This effort, which was established by the EPA in 2010, requires the Chesapeake Bay watershed’s six states and the District of Columbia to enact pollution reduction practices by 2025, with the ultimate goal of restoring the bay and its tidal rivers.

Although TMDLs are a tool to restore damaged waterways by requiring agricultural and other sources to reduce their pollution inputs, they are dependent on a waterway first being listed as “impaired,” or falling short of federal water quality standards under the Clean Water Act. Furthermore, as Hughes and Vadas point out in their review, this policy focuses on water quality and ignores agricultural impacts on other important factors like stream habitat, biodiversity, and flood tendencies—factors that riparian buffers are well suited to address.

“By farmers and scientists working together, we can both learn things from each other—we can learn how the farmers might better protect those streams and how the farmers can benefit from those protections.”

Experts emphasize, however, that riparian buffer strips are not a blanket solution to agricultural runoff. “Riparian buffers can do a really great job of mitigating agriculture to an extent, but if an entire catchment is intensively used for agriculture, buffers may not be as effective. There, they’d only be part of the solution,” said Infante.

Overall, Hughes and Vadas agree that although challenges remain, policies that protect and rehabilitate waterways can increase the probability of successful and healthy aquatic ecosystems. “Policies that encourage doing so—and discourage not doing so—are warranted,” they say in their paper. Plus, the authors both expressed hope that farmers and scientists can collaborate to find solutions that work for individual streams. “By farmers and scientists working together,” Hughes said, “we can both learn things from each other—we can learn how the farmers might better protect those streams and how the farmers can benefit from those protections.”

—Jady Carmichael (@JadyCarmichael), Science Writer

Note: Hughes and Vadas’s review was written independently, with no external financial support, and their employers were not involved in its writing or publication.

Citation: Carmichael, J. (2021), Scientists call for policies to buffer agricultural runoff, Eos, 102, https://doi.org/10.1029/2021EO210562. Published on 22 October 2021.
Text © 2021. The authors. CC BY-NC-ND 3.0
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