What is it?
Eutrophic standing water is nutrient rich and is found in lakes, canals, gravel pits and reservoirs. In the UK Biodiversity Action Plan this habitat covers natural and manmade still waters such as lakes, reservoirs and gravel pits but it excludes small pools, field ponds and brackish waters. The Biodiversity Action Plans for mesotrophic and eutrophic waters are therefore complementary and their implementation should be coordinated.
Eutrophic waters are most typical of hard water areas of the lowlands of southern and eastern Britain. Eutrophic standing waters are highly productive because plant nutrients are plentiful, either naturally or as a result of artificial enrichment. They support a wide diversity of plant and animal species. Eutrophic standing waters are significant waterfowl habitats all year round, providing breeding, feeding and winter roosting sites for a large number of species. In addition, eutrophic standing waters are important feeding areas for bats as flying insects emerge from the waters in spring.
The swamp and marsh margins of eutrophic water column typically contains at least 0.035 mg L -1 total phosphorus (which includes phosphorus bound up in plankton and 0.5 standing waters are an important habitat for aquatic invertebrates such as dragonflies and water beetles. When silt accumulates around the marginal vegetation it provides habitat for detritus feeders such as snails and crustaceans.
These water bodies are characterised by having dense, long-term populations of algae in mid-summer, often making the water green. Their beds are covered by dark anaerobic mud, rich in organic matter. Many lowland water bodies in the UK are now heavily polluted, with nutrient concentrations far in excess of these levels, although there is some geographical variation in the extent of the enrichment.
The situation in the South East
|Extent in England||67,500 ha|
|Extent in the SE region|| data to be added
|Percentage UK resource in the SE|
|Extent covered by SSSI designation|
Rate of change
|County||1998 extent (ha)||2008 extent (ha)|
|Buckinghamshire||unknown|| data to be added
|Isle of Wight||unknown|| to be added
|Kent||unknown|| to be added
|Surrey||unknown||data to be added
|Sussex||unknown|| date to be added
|Total||unknown|| data to be added
One or more of the following factors may cause a reduction in biodiversity in a eutrophic standing water. The response of any given water body is unique, as some lakes are relatively resistant to change whereas others are more sensitive.
Climate change. A substantial change in water supply and throughput would alter the character of water bodies and a rise in temperature would produce wide-ranging effects such as acceleration of plant growth.
Pollution. Pollutants find their way into these waters not only from point sources, but also from diffuse sources. Organic and inorganic fertilisers and nitrogen-rich gases cause nutrient enrichment (eutrophication) of the water, with consequent damage to plant and animal communities. Diffuse-source pollution generally exceeds that from point-sources.
Changes in land cover. These can release nutrients from the soil that may enter water bodies, causing enrichment. The long-term effect of such land-use changes is an increase in the risk of pollution and of siltation, which can smother fish spawning sites and damage aquatic vegetation. These problems are exacerbated by the removal of waterside vegetation and reed-swamp, which are effective barriers to particulate matter and act as sinks for nutrients.
Water abstraction. Abstraction for potable supply, industry or irrigation, either directly from a standing water body or from surface feeders or aquifers, can depress water levels and increase water retention time and reduced flushing rate. This may exacerbate nutrient enrichment, cause deterioration of marginal vegetation through drawdown and cause shallow lakes to dry out. For coastal sites, a reduction in the throughput of fresh water could increase the salinity of a water body.
Fishing. The introduction of fish, the removal of predators, and the manipulation of existing fish stocks for recreational fishing leads to the loss of natural fish populations and may affect plant and invertebrate communities. Heavy stocking of bottom-feeding fish such as carp Cyprinus carpio can cause turbidity and accelerate the release of nutrients from sediments. This has caused major problems of enrichment in some eutrophic water bodies.
Recreation. Use of standing waters for recreational and sporting purposes may create disturbance that affects bird populations. Marginal vegetation may suffer from trampling and the action of boat hulls and propellers destroys aquatic plants and stirs up sediment, contributing to enrichment and encouraging the growth of algae. The construction of marinas and other leisure facilities may destroy valuable habitat and can lead to increased pollution.
Non-native plants and animals. Release of non-native plants and animals can be very damaging. The signal crayfish Pacifastacus leniusculus, has had the dual impact of destabilising the biota of some waters by consuming large amounts of aquatic vegetation and eliminating many populations of native crayfish by spreading crayfish plague.
Vision for Eutrophic Lakes
The South East Biodiversity Forum’s vision for this habitat is that there should be:
No further loss of existing habitat
Good management, including visitor management, on all extant sites
No damage to site integrity from activities arising outside the sites, eg. inadequately managed public access • Re-creation of mesotrophic lakes on appropriate sites to restore some past losses, including the linking up of fragmented sites
Greater public appreciation of mesotrophic lakes and their specialist wildlife, including greater awareness of the impacts of human pressures, such as dog-walking, mountain-biking, dumping of waste
Creation of alternative green space around important mesotrophic lakes under pressure for increasing new housing, such as the Thames Basin Heaths
How we can deliver this vision
- Provision of land management advice by statutory (Natural England) and non-statutory agencies (NGOs)
- Project funding (SITA Trust, WREN etc)
- Site management plans
- Minerals after-use (http://www.afterminerals.com/)
- Land purchase/management agreements by NGOs
- River restoration linked to Water Framework Directive Programme of measures
- Catchment Sensitive Farming tackling diffuse pollution issues