Published March 8, 2019 Journal of Environmental Quality SPECIAL SECTION RIPARIAN BUFFER MANAGEMENT Current Insights into the Effectiveness of Riparian Management, Attainment of Multiple Benefits, and Potential Technical Enhancements Marc Stutter,* Brian Kronvang, Daire Ó hUallacháin, and Joachim Rozemeijer iparian buffers have been one of the most widely Abstract used management options worldwide when dealing Buffer strips between land and waters are widely applied with protection of surface waters from agricultural dif- measures in diffuse pollution management, with desired Rfuse pollution. Appropriately managed riparian areas offer mul- outcomes across other factors. There remains a need for tiple functions related to improving water quality, biodiversity, evidence of pollution mitigation and wider habitat and societal benefits across scales. This paper synthesizes a collection of 16 and climate adaptation. First, riparian areas offer possibilities new primary studies and review papers to provide the latest for protecting watercourses and lakes from inputs of sediments, insights into riparian management. We focus on the following nutrients, pesticides, and other contaminants by intercepting areas: (i) diffuse pollution removal efficiency of conventional surface runoff, tile drainage, and groundwater from adjoining and saturated buffer strips, (ii) enhancing biodiversity of buffers, agricultural fields. Second, riparian areas also offer unique bio- (iii) edge-of-field technologies for improving nutrient retention, and (iv) potential reuse of nutrients and biomass from buffers. diversity (in turn affecting in-field and in-stream biodiversity) Although some topics represent emerging areas, for other including structurally complex layers of vegetation, making well-studied topics (e.g., diffuse pollution), it remains that them attractive to many wildlife species (Naiman et al., 1993). effectiveness of conventional vegetated buffer strips for water The vegetation and habitat may be managed for many aspects quality improvement varies. The collective findings highlight including wildlife corridors, stream shading, introducing pol- the merits of targeted, designed buffers that support multiple benefits, more efficiently interrupting surface and subsurface linators, biomass, and agroforestry. Lastly, riparian areas with contaminant flows while enhancing diversity in surface diverse, often wet, moisture conditions and high plant biomass topography, soil moisture and C, vegetation, and habitat. This create soils of high organic C contents. These soils are there- synthesis also highlights that despite the significant number fore of importance for C sequestration and should be protected of studies on the functioning of riparian buffers, research gaps from draining. Overall, the importance of the semi-wet ripar- remain, particularly in relation to (i) the capture and retention of soluble P and N in subsurface flows through buffers, (ii) the ian ecotones between the aquatic environment and higher- utilization of captured nutrients, (iii) the impact of buffer design lying drier soils cannot be overestimated. and management on terrestrial and aquatic habitats and species, Depending on desired outcomes, a range of practices can and (iv) the effect of buffers (saturated) on greenhouse gas be applied to riparian areas, including exclusion of agricultural emissions and the potential for pollution swapping. cultivation and grazing, vegetation management, provision of floodwater storage, bank stabilization, and soil management to Core Ideas promote or limit certain pollution processes. The designs and • We present an updated synthesis on riparian management areas given to them are hugely diverse, ranging from smaller-scale incorporating insights from 16 new papers. riparian buffer strips (widths = 1–5 m, Fig. 1a and 1b; Stutter et • Topics cover diffuse pollution, biodiversity, new technologies, al., 2012; Haddaway et al., 2018), to rewetted riparian buffers and biomass reuse. including constructed wetlands (<1 ha; Land et al., 2016) and • The synthesis shows a move toward designed elements to larger recreated wetlands (10 to >100 ha, Fig. 1c; Kristensen et improve riparian functions. al., 2014; Land et al., 2016; Windolf et al., 2016), to engineered designs in restricted riparian spaces (Fig. 1d). Catchment and river basin managers continue to seek new solutions for improving water and ecological quality of surface waters worldwide. In the period since a previous collection on the multiple benefits of riparian buffer management (Stutter Copyright © American Society of Agronomy, Crop Science Society of America, and et al., 2012), it is perhaps the incorporation of structural Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. M. Stutter, The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK; B J. Environ. Qual. 48:236–247 (2019) Kronvang, Dep. of Bioscience, Aarhus Univ., Silkeborg, Denmark; D. Ó hUallacháin, doi:10.2134/jeq2019.01.0020 Crops, Environment and Land Use, Teagasc, Wexford, Ireland; J Rozemeijer, This is an open access article distributed under the terms of the CC BY-NC-ND Deltares, PO Box 85467, 3508 AL Utrecht, the Netherlands. license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Received 23 Jan. 2019. Abbreviations: DOC, dissolved organic carbon; EU, European Union; GHG, Accepted 11 Feb. 2019. greenhouse gas; IBZ, integrated buffer zone; SOC, soil organic carbon; SRB, *Corresponding author ([email protected]). saturated riparian buffer; VBS, vegetated buffer strip. 236 Fig. 1. A range of styles and scales of riparian management. (a) A narrow, fenced buffer zone within headwaters of the River Dee (northeastern Scotland) of regulatory compliance width but seeking additional benefits from tree planting on one bank (the sun-facing direction). (b) At a larger river scale, the River Odense (Funen, Denmark) surrounded by dry riparian buffers with grass and trees. This can be compared with (c) the rewetted riparian buffer to the remeandering of the River Skjern in 2002 (west Jutland, Denmark), one of the largest river and floodplain restoration projects in northwestern Europe. The space required for extensive riparian and channel restoration compares with (d) where buffer features enhancing riparian functions are incorporated into a 5- to 10-m-width design of stream buffer zone. These multifunctional zones can incorporate features such as ponds to intercept surface and subsurface runoff and enhance nutrient residence times in aquatic and tree-planted zones aside agricul- tural headwaters (Sillerup, Denmark). components of buffers that has most developed (see also Mander with functions for biodiversity and climate adaptation as part et al., 2017). This includes restoring functions associated with of more integrated catchment management. Evidence needs saturated ground, trees, and other vegetation and enhancing remain for broader riparian management aspects (e.g., alterna- biogeochemical processing with “treatment-train” elements such tive buffer “productivity,” enhancing aquatic ecosystem resil- as bunds, mini-wetlands, and interruption of artificial drain- ience) that will be persuasive to regulators and land managers in age. Continuing research on management interventions restor- achieving more widespread uptake (e.g., Haddaway et al., 2018; ing multiple functions of riparian buffers, and the basis of these discussed below). We need to recognize that riparian areas may functions in the natural environment, is required. provide space to incorporate new ecotechnologies (increas- Globally, water quality objectives are still not being met ingly termed “green infrastructure”) where “light” engineering in many countries, and eutrophication problems like harmful principles enhance multiple functions (Fig. 1d). algal blooms and hypoxia are increasing in many developing Key aims for this new collection of papers were (i) to combine regions like Southeast Asia (Strokal et al., 2016). In Europe, evidence of emerging designs of enhanced structural elements in the European Union (EU) Water Framework Directive incor- riparian buffers and (ii) to provide an up-to-date synthesis of rectly projected widespread attainment of waterbody Good processes and functioning in natural and managed riparian buf- Ecological Status by the end of the first river basin planning fers. This riparian management collection gathers primary inves- round in 2015 (Voulvoulis et al., 2017). In the United States, tigations and reviews from leading groups researching riparian loadings of N and P from agricultural catchments to lakes buffer functions to protect water quality, increase biodiversity, and coasts and overall success of mitigation actions are vari- and adapt to climate change. The accompanying manuscripts able (Oelsner and Stets, 2019). In Australia, efforts continue comprise 16 papers from lead authors spanning eight coun- to reverse greatly elevated river loadings of nutrients to protect tries of Europe and the United States, presented and discussed coastal ecosystems (Brodie et al., 2017). Riparian buffers, as during a special session held at a Land Use and Water Quality widely favored measures in river basin management, are often 2017 conference (the Netherlands, May 2017; www.luwq2017. poorly targeted in seeking to address pollution. Therefore, it is nl/special_sessions; Fraters et al., 2017) and supplemented by a timely to look again at riparian buffer management. Water qual- targeted