Buckinghamshire & Milton Keynes Biodiversity Action Plan Chalk Rivers Habitat Action Plan Chalk Rivers Key associated species Bewick’s Swan River Water-crowfoot Brook Lamprey River Water-dropwort Brown Trout Snipe Bullhead Spined Loach Cetti’s Warbler Water Crowfoot Grayling Water Rail Green Sandpiper Water Shrew Kingfisher Water Vole Otter Freshwater White-clawed Crayfish Reed Bunting Chalk rivers are amongst the most species-rich and productive riverine habitats and have a characteristic plant community often dominated in mid- channel by River Water-crowfoot species and Starworts, with Watercress and Lesser Water-parsnip along the edges. Such habitat provides suitable sites for a rich diversity of invertebrate life and provides important fisheries, with low banks also supporting a range of water-loving plants and associated fauna. All chalk rivers are fed from groundwater and in order for them to maintain their flow, adequate winter rainfall is needed to recharge the aquifer. In winter when more rain percolates down into the aquifer the source of the river will be higher up the valley. In summer, as the water table drops, so the source of the river moves back down the valley. These stretches of the streams with intermittent flow are known as ‘winterbournes’. A number of specialised invertebrates and plants are adapted to such conditions. Calcareous fen communities and carr woodland occur within the river corridor of chalk streams where these have not been lost to intensive agriculture or development. The characteristics of chalk streams can be summarised thus: y they are fed primarily from groundwater y the temperature of the water does not vary greatly throughout the year (2-3 degrees max) as it comes from the ground y they have a high biodiversity y they are not generally liable to flash flooding as they are little affected by direct rainfall y the source of the river will move up and down the valley through the seasons y they generally have very clear water, filtered by its passage through the chalk and gravel bed. 1 Buckinghamshire & Milton Keynes Biodiversity Action Plan Chalk Rivers Habitat Action Plan 1 Current status in UK Biological status 1.1 The soft, calcareous, porous rock known as chalk only occurs in England, France and New Zealand. In England it is found in hills (downs) and plains within a crescent extending from Dorset, through Kent, Buckinghamshire and Hertfordshire to Norfolk and East Yorkshire. The smaller rivers rising from this rock are known as chalk streams. As a result of a combination of climate, geology and human activity, they have several characteristic features, which encourage plant and animal life and make them unique. 1.2 Chalk streams are internationally important and are listed in Annex I of the European Habitats Directive as ‘floating vegetation of Ranunculus of plain and submountainous rivers’. England has the majority of this resource in Europe and therefore has special responsibility for the conservation and enhancement of chalk streams systems. This status was reflected in the UK Biodiversity Steering Group Report, which prioritised chalk rivers as a key habitat. The 2007 Habitats and Species Review proposed that rivers be defined as a UK BAP Priority Habitat with the inclusion of Chalk Rivers within this wider definition. However the Chalk Rivers in Buckinghamshire are considered such a priority for the county Biodiversity Action Plan that the separate Chalk Rivers HAP has been retained. 1.3 The characteristic plant community of chalk streams is often dominated in mid-channel by Water-crowfoots and Water-starworts, whilst Watercress and Lesser Water-parsnip grow along the edges. They have low banks which support a range of water-loving plants. The adjacent riverside habitats are often of considerable value for wildlife. Wet meadows may provide areas of species-rich grassland and are particularly important for breeding birds such as Redshank and Snipe. 1.4 All chalk streams are fed from groundwater aquifers, producing clear waters and a generally stable flow and temperature regime. These conditions and the gravel substrate support a rich diversity of invertebrate life and important fisheries, notably for brown trout. Brook Lamprey, Salmon, Freshwater White-clawed Crayfish and otter are among the species listed on Annex II of the EC Habitats Directive that chalk streams support. Most chalk streams have winterbourne stretches in their headwaters. These often run dry, or partially dry, in late summer because of lack of rainfall recharging the aquifer. A characteristic range of invertebrates has adapted to these conditions, as has the pond Water-crowfoot. 2 Buckinghamshire & Milton Keynes Biodiversity Action Plan Chalk Rivers Habitat Action Plan 2 Current status in Buckinghamshire Cover and distribution 2.1 The chalk streams of the Chilterns are an important component of the wildlife resource of Buckinghamshire. The river valleys contribute a great deal to the character and quality of the Chilterns landscape and they support distinctive wildlife communities. Buckinghamshire has a number of chalk streams running to the south of the Chilterns, namely: River Chess, River Misbourne, River Wye, and Hughenden Stream. Trends 2.2 Since forest clearance around 1000 BC, chalk streams have been heavily influenced by human activities. The Romans and Saxons started building water mills. Impoundments on the streams resulted in localised decreases in gradient and stream flow energy, resulting in siltation and a reduction in dissolved oxygen. They also caused a problem for the passage and migration of aquatic invertebrates and fish. Drainage of the fields in the valley bottoms reached a climax between 1650 and 1900 in the elaborate system of water meadows. As the population of the valleys increased, human and animal sewage affected the chalk rivers (today it is mostly discharged as well-treated effluents), increasing the amount of phosphorus entering the water. 2.3 Intensive agriculture in conjunction with drainage has destroyed wetlands and degraded the river corridor and has led to increased nutrients and sediments within the rivers. Urban pressures can lead to bank reinforcement and the loss of river corridor. Modification of the temperature, mineral and organic content of the water will affect plant and animal life as will the introduction of non-native species such as rainbow trout and signal crayfish. More and more subterranean water is abstracted from the chalk for human use, which has sometimes reduced the flow. 3 Current factors affecting the habitat Pollution 3.1 Discharge of effluent arising from sewage treatment works, industry and agriculture, including point and diffuse sources, leads to high nitrate and phosphate levels, causing eutrophication and acidification. Abstraction 3.2 Excessive ground water and surface water abstraction, results in low flows and reduced dilution of pollutants. Loss of riverine habitats and floodplain 3.3 This can include artificial channel modification, construction of dams and reservoirs, insensitive land drainage and flood defence works. 3 Buckinghamshire & Milton Keynes Biodiversity Action Plan Chalk Rivers Habitat Action Plan Inappropriate land use and bank management 3.4 This can result from intensive agriculture, overgrazing and allowing cattle uncontrolled access to banks. Insensitive fisheries management 3.5 Poor management can lead to reductions in native animal and plant populations. Invasive species 3.6 Invasive plant and animal species can be introduced or arrive naturally and result in a loss of habitat quality. Climate change 3.7 This may result in different hydrological regimes and extreme environmental effects. Development 3.8 This may include industrial and housing development within the floodplain. Recreation 3.9 Recreation can cause disturbance and erosion and lead to a loss of habitat quality. 4 Current action Legal status 4.1 The Environment Act came into force in 1995. Under this Act, the Environment Agency has two primary statutory duties in respect of conservation interest. *To further, wherever possible, conservation when carrying out water management functions. This also applies to Freshwater Fisheries Act 1975, Land Drainage Bylaws and Water Resources Act 1991, and licensing functions. *To have regard to sites of special conservation interest when carrying out pollution prevention and control functions. 4.2 In fulfilment of these duties the Environment Agency seeks to conserve and enhance the water environment when carrying out all its regulatory and advisory activities. 4.3 As a statutory planning consultee the Environment Agency also applies these duties and a free-standing duty, generally, to promote the conservation of natural beauty and amenity, and the wildlife dependant on the aquatic environment, to seek to influence structure plans, major development and individual planning applications. 4 Buckinghamshire & Milton Keynes Biodiversity Action Plan Chalk Rivers Habitat Action Plan 4.4 The Conservation (Natural Habitats etc) Regulations 1994 states the importance of rivers and other linear features as wildlife habitats and mechanisms for dispersal. As such their protection and management is encouraged. This is also recognised in DOE PPG 9 Nature Conservation. 4.5 Agri-environment schemes can help to protect chalk streams. For example, in the Chilterns Area, Environmental Stewardship objectives include Arable Margins for the conservation of river valleys and chalk streams by provision of arable field margins to link and buffer