Constructed Farm Wetlands - Treating Agricultural Water Pollution and Enhancing Biodiversity Produced by Wildfowl and Wetlands Trust with Natural England
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Constructed farm wetlands - treating agricultural water pollution and enhancing biodiversity Produced by Wildfowl and Wetlands Trust with Natural England Mackenzie, S.M. and McIlwraith, C.I. May 2013 This guidance is aimed at farm advisers, primarily Catchment Sensitive Farming Officers, as well as other Natural England and Environment Advisers working with farmers. The aim is to provide further information and examples on the use of constructed wetlands and sustainable drainage systems on farms. These wetland features can reduce diffuse water pollution from agriculture as well as improving biodiversity and other benefits. Different types of constructed wetlands and sustainable drainage systems are described, with guidance on their suitability for different farm situations and pollution issues, location, design, costs, permits required and case studies. Foreword Rivers, lakes, ponds and coastal waters are important habitats and part of our landscape, as well as providing drinking and bathing water. Water quality and biodiversity have improved dramatically but are still impacted by diffuse water pollution from agriculture. Constructed wetland systems can be designed to create wetland habitats, reduce pollution on farms, control flooding and enhance public enjoyment of the countryside. In order to be effective their design needs to be appropriate for the site and pollutant issues and this guidance aims to give an introduction to constructed farm wetlands and where to seek further advice and support. Catchment Sensitive Farming (CSF) provides training and support to farmers on a range of farm practices and infrastructure improvements that reduce diffuse water pollution from agriculture. Constructed wetlands and sustainable drainage systems (SuDS) can be used to trap and treat pollutants, as part of a CSF approach to tackling agricultural pollution. Wildfowl and Wetlands Trust (WWT) have experience in design, construction and maintenance of constructed wetlands for treating pollutants and creating wetlands and amenity features at sites across the world. WWT worked with CSF to develop this guidance for advisers, on the role of constructed wetlands and sustainable drainage systems on farms. How and where to use these options, singly or in combination, to reduce the source of a pollutant, break the pathway of pollution and protect water bodies or sensitive habitats is described. Philippa Mansfield, Catchment Sensitive Farming Contacts for this publication Head of Wetlands for Water [email protected] Sally Mackenzie Wildfowl & Wetlands Trust http://www.wwt.org.uk/ Trust Project officer - Wetlands [email protected] Catherine McIlwraith for Water Wildfowl & Wetlands http://www.wwt.org.uk/ [email protected] Philippa Mansfield Catchment Sensitive Farming http://www.naturalengland.org.uk/csf Cover photo, Fabrice Gouriveau Contents 1 Introduction ................................................................................................... 1 1.1 Why use wetlands? ................................................................................... 2 1.2 Type of water that can be treated ............................................................... 2 1.2 How are wetlands used ................................................................................. 4 1.3 Multiple benefits (Ecosystem services) ......................................................... 5 1.4 Limitations of using wetlands ...................................................................... 6 2 Types of farm wetlands .................................................................................... 7 2.1 Summary table of wetland options .............................................................. 8 2.2 General consent issues ............................................................................ 11 2.3 Lining .................................................................................................... 12 3 Farm wetland options .................................................................................... 13 3.1 Swales (1-2 Star systems) ....................................................................... 13 3.2 In-ditch wetlands (2-3 Star systems) ........................................................ 17 3.3 Sediment ponds (2 star systems) .............................................................. 21 3.4 Constructed wetlands (3-5 Star systems) ................................................... 26 4 Complementary Measures – Woodlands ........................................................... 37 5 Funding sources ............................................................................................ 38 5.1 The CSF Capital Grant Scheme ................................................................. 38 5.2 Environmental Stewardship ...................................................................... 38 6 Management of wildlife during creation & management of wetlands ..................... 42 7 Suitable Planting Schemes ............................................................................. 43 8 Further sources of information ........................................................................ 45 9 References ................................................................................................... 46 10 Annex I Case studies .................................................................................. 49 10.1 In ditch wetlands ................................................................................. 49 10.2 Sediment ponds ................................................................................... 52 10.3 Constructed wetlands for diffuse effluent ................................................ 54 10.4 Constructed wetlands for high strength point source effluent ..................... 58 Contributing authors Fabrice Gouriveau, Dianne Mathews, Philippa Mansfield & Louise Webb Acknowledgements We would like to thank Tim Bushell (Natural England), Jamie Letts (Environment Agency), James Grischeff (Catchment Sensitive Farming), Kirstie Richardson-Bull (Environment Agency), Andy Graham (Wildfowl & Wetlands Trust) and Rob Shore (Wildfowl & Wetlands Trust) for their contribution and comments on this document. We are also very grateful to Des Kay (Catchment Sensitive Farming/Natural England), Kathryn Mitchell (Linking Environment and Farming), Stuart Moss (Catchment Sensitive Farming) and John Renner of Bellshill Farm for providing case studies and information to illustrate examples of wetland features in action. Whilst the Wildfowl and Wetlands Trust and Natural England have used their best endeavours to ensure the accuracy of the guidance, we cannot accept any responsibility for any liabilities arising from its use. 1 Introduction The purpose of the guidance is to provide a basic introduction to the benefits and use of farm wetlands to reduce diffuse water pollution from agriculture (DWPA) and enhance biodiversity. The aim is to provide guidance on the options, suitability, placement, design, construction and cost of farm wetlands and sustainable drainage systems. In this guidance a broad definition of farm wetlands is used to cover rural sustainable drainage systems (Rural SuDS), including sediment ponds and traps, bunds and swales, as well as the creation of artificial wetlands to improve water quality and how these options can be used together. Please refer to Section 3 for more information on each of these features. The aim is to enable Catchment Sensitive Farming Officers (CSFOs) and other advisers, including Natural England local land management advisers and Environment Agency Officers, to understand how and where to use these options, as part of a suite measures that could be implemented on farms to reduce water pollution. Farm wetlands can be used to treat and control pathways of agricultural pollutants, provide some attenuation of flood flow and create wildlife habitats and public access opportunities (See Figure 1). They can be used as an additional option to the existing suite of measures available and require careful targeting and design as part of an overall farm water management plan. Figure 1. Farm swale (WWT) – see section 3. This guidance will build on existing available information and cover a range of wetland options from simple easily created options to treat lightly contaminated water to multi- stage treatment systems which are designed to treat point source high strength wastewater. Depending on the nature of the wastewater, designs will vary in complexity from those the farmer can easily create to something which requires more technical support. 1 1.1 Why use wetlands? Wetlands can be used to improve water quality. They can successfully treat a range of pollutants associated with agricultural wastewater including: Biological Oxygen Demand, suspended solids, ammonia, nitrate, phosphate, faecal indicator organisms (FIO’s) and some pesticides. With careful and specific design wetlands provide many opportunities for wildlife habitat especially if receiving less contaminated water. They are a practical, sustainable, environmentally friendly, aesthetically pleasing option to treating contaminated water in rural areas They can be designed to provide additional benefits such as biofuels, e.g. using willow coppice systems and for wildlife. 1.2 Type of water that can be treated Wetlands can be used to treat lightly contaminated water from farmyards or as a result of run-off from roads, tracks and fields. They are one of the