Ecological Engineering 52 (2013) 252–261 Contents lists available at SciVerse ScienceDirect Ecological Engineering jo u r n al hom ep age: www.elsevier.com/locate/ec oleng Riparian buffer located in an upland landscape position does not enhance nitrate-nitrogen removal Sara R. Johnson a,b , Michael R. Burchell II b,∗ , Robert O. Evans b , Deanna L. Osmond c , J. Wendell Gilliam c a AMEC Environment & Infrastructure, Inc., 3800 Ezell Road, Suite 100, Nashville, TN 37211, United States b Department of Biological and Agricultural Engineering, Box 7625, North Carolina State University Campus, Raleigh, NC 27695, United States c Department of Soil Science, Box 7619, North Carolina State University Campus, Raleigh, NC 27695, United States a r t i c l e i n f o Article history: Received 28 March 2012 Received in revised form 31 July 2012 Accepted 13 November 2012 Available online 25 December 2012 Keywords: Riparian buffer Conservation programs Groundwater Hydrology Nitrate NO3 - -N a b s t r a c t Relatively narrow (<50 m) riparian buffers strategically reestablished in correct landscape positions have been shown to significantly reduce agricultural non-point source pollution to streams. Because of this, conservation programs have been established to encourage landowners to enroll lands near surface waters to improve water quality. Former cropland enrolled in a conservation program was evaluated to deter- mine its effectiveness in reducing nitrate-nitrogen (NO 3 - -N) in shallow groundwater. This conservation buffer (CB) was up to 80 m wide and was planted with loblolly pine (Pinus taeda). It was situated upslope of an existing 30–60 m wide riparian hardwood forest buffer (EHB) located within the floodplain of an intermittent stream. Shallow groundwater NO 3 - -N, groundwater hydrology, total organic carbon, and soil redox potential were measured throughout both the CB and the EHB for 18 months. Groundwater NO 3 - -N concentrations, often 5–15 mg L -1 within the CB, were not significantly reduced from concen- trations that entered from the agricultural field edge. However, a decrease in NO 3 - -N concentration was observed within the EHB (17–83%). The hydrology of the CB coupled with relatively low organic carbon contributed to a low denitrification potential and lack of NO 3 - -N reduction compared with the EHB. While the CB enrollment likely provided additional habitat benefits it did not appear to provide treatment of groundwater NO 3 - -N. It is our conclusion that landscape position is a more important defining variable for buffer site selection than buffer width if NO 3 - -N reduction is a primary goal. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Riparian buffers have been used to improve and protect water quality from non-point source pollution. They have also been praised for their ability to enhance wildlife and aquatic habitat along watercourses. Pollutant removal within riparian buffers can be divided into two categories, surface and subsurface. Pollutants that are removed on the surface of the riparian buffer are sedi- ments and nutrients such as phosphorus. They are most effectively trapped by grasses, brush and shrubs that are located in upland buffer zones. Removal of subsurface pollutants such as groundwa- ter NO 3 - -N, can take place through plant uptake or through the microbial mediated process of denitrification which transforms it to gaseous nitrogen end products, primarily dinitrogen gas (N 2 ) and nitrous oxide (N 2 O) (Madigan et al., 2000). Removal of NO 3 - -N by Abbreviations: NO3 - -N, nitrate-nitrogen; Cl - , chloride; DOC, dissolved organic carbon; TOC, total organic carbon; CB, conservation buffer; EHB, existing hardwood buffer; redox, reduction/oxidation. ∗ Corresponding author. Tel.: +1 919 513 7372; fax: +1 919 515 6772. E-mail address: mike burchell@ncsu.edu (M.R. Burchell II). plant uptake is generally considered to be temporary in buffers that are unmanaged, because nutrients are cycled back into the soil–water system when plant material decays (Fail et al., 1987; Haycock and Pinay, 1993). Denitrification results in permanent removal of NO 3 - -N, and studies have shown that riparian buffers can significantly improve water quality by reducing the amount of NO 3 - -N discharged to receiving watercourses in groundwater (Peterjohn and Correll, 1984; Gilliam, 1994; Gilliam et al., 1997; Lowrance et al., 1997; Dukes et al., 2002; Spruill, 2004). Some researchers have reported reductions in groundwater NO 3 - -N con- centrations that exceed 90% in riparian buffers located in ideal landscape positions (Lowrance, 1992; Lee et al., 2000). Conservation programs have been established to encourage the enrollment of crop or pasture land near streams that can be restored to riparian buffers and improve water quality. The goal for these enrollments is to maximize stream miles protected, so ideally, lands that provide maximum water quality protection per hectare should be targeted for enrollment. Often enrollment criteria are based solely on proximity to a watercourse and width. While wider riparian buffers can enhance ecosystem services such as habitat, the increased width does not always significantly improve water quality function (Palone and Todd, 1997; Mayer 0925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2012.11.006