Vegetated buffers and swales

Vegetated buffers and swales

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Other name/s

Vegetated buffers and swales, filter strips, riparian buffers

Description

Vegetated buffers and swales for agricultural water quality improvement are drainage features that separate an agricultural production area from a waterway or wetland. Buffers are usually located perpendicular to water flows whereas swales are located parallel to the flow and convey water in a drainage line (as shown in the diagrams above). The difference between swales and drains, is that swales are dry most of the time whereas drains hold water for longer periods.

Vegetated buffers and swales are often used as a best management practice tool in agricultural production systems to prevent erosion, such as a grassed interrow or headland. They can have a secondary benefit as a treatment system by slowing water flow and depositing coarse sediment and some nutrients, although their effectiveness in treating agricultural run-off varies depending on site conditions and their design and management[6][7]. Buffers can be efficient at removing nitrogen from groundwater[5], but efficiency is strongly influenced by specific site characteristics, such as groundwater flow paths and soil saturation[5][3] Nitrogen can also be transformed through various processes in a buffer or swale, depending on water flow through the system which will vary seasonally. Most of the content on this webpage focuses on removal of sediments or sediment-bound nutrients in surface run-off.

Vegetated buffers and swales help protect wetlands and waterways from the impact of adjacent land uses and can also protect agricultural land from flooding and bank erosion. Swales typically contain grass. Buffers can be vegetated with native plants including sedges, grass, trees or shrubs and the type of vegetation influences the services that buffers can provide.

A grass buffer located immediately adjacent to a cropping area has been shown to be more effective than trees for treating run-off while deep rooted trees in the riparian area are more effective for bank stabilisation[7][1]. A buffer with grass closest to the agricultural production area and trees adjoining the receiving environment could therefore help achieve multiple water quality, bank stabilisation and habitat benefits (Figure 1). For more information on the different buffer designs and principles for different services or benefits, refer to the Queensland Wetland Buffer Planning Guideline.

When used as a treatment system, vegetated buffers and swales work by increasing the roughness of the ground surface and therefore increasing friction, which slows the water and allows settling of coarse to medium sediments and some particulate nutrients and pesticides. By slowing the flow velocity, water is given more opportunity to infiltrate into the soil. Infiltration of water into the soil is the most efficient way for vegetated structures to assist in removal of finer sediments (e.g. less than 40μm (microns) in diameter), nutrients and pesticides[4]. In some cases, pollutants can also be removed through adsorption to the plant or soil material[7] or uptake by vegetation[8].

Vegetated buffers and swales are best positioned as one of the first components in a treatment train to prevent erosion and enable trapping of coarse to medium sediments prior to run-off entering other treatment systems. They provide an important pre-treatment function for other elements in a treatment train.

Services and benefits

• Bank stabilisation
• Soil conservation, preventing erosion
• Water treatment (sediment, some nutrients and pesticides)
• Spray-drift management
• Wildlife habitat and corridor

While buffers can provide many services the focus of this content is on water quality improvement

References

1. ^ Department of Employment, EDI (2011), Wetland Management Handbook: Farm Management Systems (FMS) guidelines for managing wetlands in intensive agriculture.. [online], Queensland Wetlands Program, Brisbane. Available at: https://wetlandinfo.des.qld.gov.au/resources/static/pdf/resources/reports/fms/fms_025_handbook_web.pdf.
2. ^ Ekka, SA, Rujner, H, Leonhardt, G, Blecken, GT, Viklander, M & Hunt, WF (February 2021), 'Next generation swale design for stormwater runoff treatment: A comprehensive approach', Journal of Environmental Management. [online], vol. 279, p. 111756. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0301479720316819 [Accessed 12 April 2022].
3. ^ King, SE, Osmond, DL, Smith, J, Burchell, MR, Dukes, M, Evans, RO, Knies, S & Kunickis, S (July 2016), 'Effects of Riparian Buffer Vegetation and Width: A 12-Year Longitudinal Study', Journal of Environmental Quality. [online], vol. 45, no. 4, pp. 1243-1251. Available at: http://doi.wiley.com/10.2134/jeq2015.06.0321 [Accessed 12 April 2022].
4. ^ Liu, X, Zhang, Z & Zhang, M (2008), 'Major factors influencing the efficacy of vegetated buffers on sediment trapping: A review and analysis', Journal of Environmental Quality, vol. 37, pp. 1667-1674.
5. ^ a b Mayer, PM, Reynolds, SK, McCutchen, MD & Canfield, TJ (July 2007), 'Meta-Analysis of Nitrogen Removal in Riparian Buffers', Journal of Environmental Quality. [online], vol. 36, no. 4, pp. 1172-1180. Available at: http://doi.wiley.com/10.2134/jeq2006.0462 [Accessed 12 April 2022].
6. ^ McKergow, LA, Prosser, IP, Grayson, RB & Heiner, D (2004), 'Performance of grass and rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water quality.', Australian Journal of Soil Research, vol. 42, no. 4, pp. 485-498.
7. ^ a b c Reichenberger, S, Bach, M, Skitschak, A & Frede, H (2007), 'Mitigation strategies to reduce pesticide inputs into ground- and surface water and their effectiveness; a review.', Science of the Total Environment, vol. 384, pp. 1-35.
8. ^ USDA (2000), Conservation buffers to reduce pesticide losses.. [online], USDA Natural Resources Conservation Service. Available at: https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_023819.pdf.

Last updated: 5 November 2022