NRMRL NATIONAL RISK MANAGEMENT RESEARCH LABORATORY GROUND WATER AND ECOSYSTEMS RESTORATION RESEARCH Effectiveness of Riparian Buffers Background Bioreactive nitrogen (nitrite and nitrate) is a non-point source pollutant that impacts ecosystem function and threatens human health. Riparian zones, the vegetated region adjacent to streams and wetlands, are effective at intercepting and controlling nitrogen and sediments entering water bodies. EPA investigated the biogeochemical, hydrological, and biological factors that govern the structure and function of riparian zone ecosystems. Improved understanding of riparian ecosystems is necessary to identify effective restoration approaches that best sustain ecosystem sendees, such as nutrient processing and sediment capture. Objectives • Quantify biotic and abiotic mechanisms control nitrogen removal in riparian soils and stream bed sediments • Identify optimal widths of riparian buffers for nitrogen and sediment control • Assess biotic responses to riparian restoration and identify the best ecological indicators to assess ecosystem recovery Approach EPA evaluated the importance of riparian buffer width on nitrogen control and surveyed the effectiveness of current state and federal regulations. EPA surveyed the scientific literature containing data on riparian buffers and nitrogen concentration in streams and ground water to identify trends between nitrogen removal effectiveness and buffer width, hydrological flow path, and vegetative cover. Major Findings The research shows that riparian buffers can significantly reduce nitrogen loads entering streams and, thus, represent important nutrient best management practices (BMPs) for land managers. Though riparian buffer efficiency varied widely among individual studies, EPA meta-analysis found important trends. While some narrow buffers (up to 25 meters) proved effective, buffers wider than 50 meters more consistently removed significant amounts of nitrogen. Buffers of various vegetation types were equally at removing nitrogen, but buffers with grassy vegetation were more effective when wider. Another strong trend in the data showed that subsurface removal of nitrogen was far more efficient than removal at or near the soil surface. Other important patterns observed among the studies reviewed indicated that nitrogen control peaks when: • Buffers extend along both stream banks, allowing greater opportunity for plant uptake • Buffers are maintained at stream headwaters The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. www.epa.gov/nrmrl for Managing Nitrogen ------- Water flow (overland and subsurface) is evenly distributed and soil infiltration rates are high Anaerobic conditions persist in the subsurface Sufficient organic carbon is present Publications Mayer, P.M., S.K. Reynolds, M.D. McCutchen, and T.J. Canfield. (2007). "Meta-Analysis of Nitrogen Removal in Riparian Buffers." Journal of Environmental Quality, 36: 1172-1180. Research Shows Importance of Riparian Buffers for Aquatic Health - Science in Action (PDF) 'J £ 'jf Sufatrficc y=|.4»ln^>»^4,V ¦. 4>; St* face: .v=».2*lw *)-2l3 Rz*a.2<* ASalK Vegetati ve Cove r Type _50 iii l11 Li i illj Uj ttl tu'ili»iiJ ui til Li xInl lJuji 0 25 50 75 100 125 150 175 200 225 250 Buffer Width (m) The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. ------- |