M2 PM Non-Point Source Pollution and TMDLs
Monday, 14 November 2005: 1:50 PM - 5:30 PM in Ballroom 2

(REY-1117-836370) Riparian buffer width, vegetative cover, and nitrogen removal effectiveness: A review of current science and regulations.

Reynolds, S¹, Mayer, P¹, McCutchen, M², Canfield, T¹, ¹ US Environmental Protection Agency, National Risk Management Research Laboratory, Ada, Oklahoma, USA² East Central University, Ada, Oklahoma, USA

ABSTRACT- Riparian zones, the vegetated region adjacent to streams and wetlands, are thought to be effective at intercepting and controlling nitrogen loads entering water bodies. Buffer width may be related to nitrogen removal efficiency by influencing nitrogen retention through plant sequestration or removal through microbial denitrification. We surveyed peer-reviewed scientific literature containing data on the relationship between riparian buffer width and nitrogen concentration in streams and groundwater of riparian zones to identify trends in the relationship between buffer width and nitrogen removal capacity. We also examined Federal and State regulations regarding riparian buffer widths to determine if such legislation reflects the current scientific understanding of buffer effectiveness. While some narrow buffers (< 15 m) removed significant proportions of nitrogen, others contributed to nitrogen loads in riparian zones. Larger buffers (> 50 m) appeared more certain to remove significant portions of nitrogen. Subsurface removal of nitrogen was efficient but did not appear to be related to buffer width. Surface removal of nitrogen was partly related to buffer width, but was generally inefficient, removing only a small fraction of the total nitrogen flowing through soil surface layers and, in some cases, actually contributing to nitrogen loads. Type of vegetative cover was not related to nitrogen removal effectiveness in the subsurface but was in surface flow. The general lack of vegetation or width effects on nitrogen removal, especially in the subsurface, suggests that soil type, watershed hydrology and subsurface biogeochemistry may be more important factors due to their influence on denitrification. State and Federal guidelines for buffer width also varied widely but generally were consistent with the peer-reviewed literature on effective buffer width, recommending or mandating buffers 15-30 m wide.

Key words: riparian buffer, nitrogen, attenuation, groundwater