Pressures and Impacts
Several occurrences may cause a reduction in biodiversity in 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:
A potential threat, which may override all the others, is 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.
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 can release nutrients from the soil and these 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 which acts as an effective barrier to particulate matter and a sink for nutrients.
Water 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 reduce 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.
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, can cause turbidity and accelerate the release of nutrients from sediments. This has caused major problems of enrichment in some eutrophic water bodies.
Use of standing waters for recreational and sporting purposes may create disturbance which 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 Use of standing waters for recreational and sporting purposes may create.
Release of non-native plants and animals can be very damaging. The signal crayfish 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.
In their natural state, eutrophic waters have high biodiversity. Planktonic algae and zooplankton are abundant in the water column, submerged vegetation is diverse and numerous species of invertebrate and fish are present.
Bottom-dwelling invertebrates such as snails, dragonflies and water beetles are abundant and calcareous sites may support large populations of the native freshwater crayfish.
Coarse fish such as roach, tench and pike are typical of eutrophic standing waters but salmonids also occur naturally in some. Amphibians, including the protected great crested newt, are often present and the abundance of food can support internationally important bird populations.
Loch Leven in Scotland and Lough Neagh in Northern Ireland, for example, each support over 20,000 waterfowl, including large numbers of wintering whooper swan. Loch Leven is nationally important for breeding ducks, such as wigeon, gadwall and shoveler, and Lough Neagh is of national importance for breeding great crested grebe.
For centuries, periodic ‘blooms’ of blue green algae, which may be natural phenomena, have been documented in Llyn Syfaddan (Llangorse Lake), South Wales and in the meres of the West Midlands.
Lakes change naturally over time, slowly filling with silt and vegetation and usually, in the absence of human impact, gradually becoming less fertile. In water bodies which are heavily enriched as a result of human activity, biodiversity is depressed because planktonic and filamentous algae (blanket-weed) increase rapidly at the expense of other aquatic organisms. Sensitive organisms, such as many of the pondweed Potamogeton and Stonewort Chara species, then disappear and water bodies may reach a relatively stable but biologically impoverished state.
Lake and Reservoir Protection
The upland tracts of land in the UK have, for many years, represented a valuable resource for a number of differing activities and these have largely co-existed without mutual disadvantage.
However, as with many aspects of life in the 20th and 21st centuries, the pressures upon these parts of our natural environment have increased substantially, to the extent that conflicts of interests are becoming increasingly evident.
In many parts of the country, where upland water supply systems are common, local geology is such that the land is very sensitive to disturbance. In mid-Wales, for example, a thin surface layer of peat overlies fluvial deposits which include red marls, responsible for serious water quality problems when exposed by ploughing and drainage works. Many rivers, streams, lakes and reservoirs have become degraded, largely through the increased impact of man’s activities, resulting in poor water quality, poor wildlife habitat, increased flooding and reduced amenity and aesthetic value. The way that we use water has a direct impact on the natural environment. This means that we must have a plan for the management of water that will protect the long-term future of the environment while encouraging sustainable development.
A number of safeguards have been put in place to enable the restoration and rehabilitation of degraded water bodies. The Environment Agency, Natural Resources Wales, the Scottish Environment Protection Agency and the Northern Ireland Environment Agency all have a duty to secure the proper use of water resources throughout the UK. They monitor water in the environment and issue ‘abstraction licences’ to regulate who can take water from the environment. These specify the amount of water someone can take from a location over a period of time. They also have long-term strategies for water resources that looks 25 years ahead and considers the needs of both the environment and society. The Water Framework Directive has established a new, integrated approach to the protection, improvement and sustainable use of surface waters (see accompanying Information Notes on the Water Framework Directive).
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