Risk Management Research
USEPA. Mayer, P. M. AND T. J. Canfield. (2008). "Research Shows Importance of Riparian Buffers for Aquatic Health." Publication No. EPA/600/F-07/004.
Excess nitrogen from fertilizer, septic tanks, animal feedlots, and runoff from pavement can threaten aquatic ecosystem health. Riparian buffers -- the vegetated region adjacent to streams and wetlands -- are thought to be effective at intercepting and controlling excess nitrogen. Resource managers often ask how wide a riparian buffer zone should be to effectively control nitrogen loads entering water bodies. Scientists at the U.S. Environmental Protection Agency’s Office of Research and Development evaluated the importance of riparian buffer width on nitrogen control. Science Objective: The objectives of research on riparian buffers are twofold: to identify the importance of riparian buffer width on nitrogen control and to determine if federal and state regulations regarding riparian buffer widths corresponded to the current scientific understanding of buffer effectiveness. ORD scientists surveyed all known scientific studies of the effectiveness of riparian buffers to identify causation and trends in the relationship between buffer width and nitrogen removal capacity. ORD scientists also surveyed federal and state laws and guidelines for maintaining riparian buffers to protect water resources. They found that nitrogen removal effectiveness varied widely among riparian zones studied, but important and consistent trends emerged. Nitrogen moving in water beneath the soil surface was much more effectively removed in riparian buffers than when nitrogen flowed in water moving across the soil surface. While some narrow buffers (1-25 meters) were effective at removing significant proportions of nitrogen, wider buffers (greater than 50 meters) more consistently removed significant portions of nitrogen. Buffers of various vegetation types such as forests, grasslands, and mixtures of grass and forest were equally effective at removing nitrogen. Further research quantified the mass of nitrogen that might be removed under various combinations of buffer width, water flow path, and vegetation type. Soil type, watershed hydrology, and the amount of nitrogen inputs to the buffer also are important factors dictating nitrogen removal effectiveness in buffers. Application and Impact: This EPA research effort represents the most current, comprehensive review of nitrogen removal in riparian buffers. The 2005 EPA report on nitrogen removal effectiveness in riparian buffers has been accessed more than 50,000 times since being made available on the internet. This information can be used by natural resource managers to develop effective riparian management plans that employ buffers as a best management practice (BMP) to control excess nitrogen in watersheds, especially when employed in conjunction with control and reduction of point and non-point sources of nitrogen from atmospheric, terrestrial, and aquatic inputs.
Paul Mayer, Ph.D.
Ecologist, EPA’s National Risk Management Research Laboratory
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