Eutrophic standing water is a fancy name for still water rich in nutrients. Ponds, lakes, canals, gravel pits and reservoirs are all examples of eutrophic standing water.
The two main nutrients required for plant growth (nitrogen and phosphate) are present at high levels. These nutrients occur naturally or come from a number of external sources such as industry, sewage works and chemicals used on agricultural land. Phosphates are produced from animal waste products, including human sewage. Conventional waste treatments do not remove phosphates and lakes in areas with large populations can suffer from this type of pollution. Phosphates can be removed from waste but that is expensive. Nitrogen comes mainly from agricultural sources where it is used as a fertilizer.
The high nutrient levels make these bodies of water very productive, with dense populations of algae in mid summer often making the water green. Some naturally eutrophic waters get so polluted with these nutrients that they are classified as hypertrophic (a shortage of oxygen).
The estimated the area of eutrophic water in Northern Ireland at 940 km2 which is slightly over 52% of the total UK resource. The total surface area of all lakes represents about 4.5% of the total surface area of Northern Ireland.
A great example of eutrophic standing water is Lough Neagh - the largest lake in Northern Ireland. Five of the six counties share a part of the edge of Lough Neagh and a third of all rainfall in Northern Ireland drains into Lough Neagh.
Lough Neagh is hypertropthic, which means that, although it is a naturally eutrophic standing water, levels of nutrients are much higher than they should be, reflecting the impact of human activities in the catchment area.
Lakes can be formed by a number of natural or artificial processes. Glaciers or landslides, for example, can form natural lakes. Artificial processes such as quarrying can form man-made lakes. Either way they can be an important freshwater habitat and support a wide variety of species.
Lakes are a popular amenity for people too, for water sports, fishing and general recreational use. This can bring tourists into rural areas and can be beneficial to the local community. Lakes can tell us a lot about levels of environmental pollution and climate change over the years can be measured by the sediment at the bottom of the lake. It is easy for lakes to be polluted by human use and it is important that action is taken to preserve these valuable habitats
A lot of our agricultural, domestic and industrial water requirements are supplied from surface water, around half of which is contained in lakes.
In their natural state eutrophic standing waters have a high biodiversity. Plankton and algae are plentiful and together with the submerged vegetation they support a large variety of species.
Aquatic plants of eutrophic standing water vary with the area, nutrient concentration and exposure. They include duckweeds, white water-lily, yellow water-lily and spiked water-milfoil. Submerged aquatic plants are usually restricted to shallow waters owing to poor light penetration.
Dragonflies, water beetles, stoneflies and mayflies are found in eutrophic standing water habitats. Bottom-dwelling invertebrates such as snails and the larval stages of non-biting midges, dragonflies, water beetles and shrimps are abundant. Several introduced fish species such as roach have become established and are now accepted as part of the biodiversity associated with standing open water. Loughs also support other coarse fish such as trench and pike. Lough Neagh is an important breeding ground for Atlantic salmon. These salmon migrate from the Atlantic Ocean, up the Lower River Bann and into Lough Neagh. This migration can take place during any month of the year but is particularly pronounced in late summer and early autumn.
Amphibians including frogs and newts may be present in the water.
Eutrophic standing waters and the area surrounding them are important for a number of bird species, such as the whooper swan, tufted duck, cormorant and graylag geese. The marginal habitats support important breeding wader and wildfowl populations including snipe redshank, lapwing, curlew and shoveler.
Eels are also abundant in some eutrophic habitats. After crossing the Atlantic Ocean as young eels they change into elvers and swim into freshwater during the spring months. They then live in freshwater for at least seven or eight years during which time they are called yellow eels and grow to over 40cm in length. After this time the eels turn silvery in appearance and stop feeding prior to their seaward migration during autumn and early winter to complete their life cycle somewhere in the Sargasso Sea. The yellow eel and the silver eel are both harvested and the Lough Neagh Eel Fishery is one of the largest fisheries in Europe. Eel numbers have declined in recent times across Europe, and this has been evident in Lough Neagh.
Lakes change naturally over time. They fill with silt and plants and, without human intervention, gradually become less fertile. In bodies of water that have become enriched with nutrients as a result of human activity, biodiversity is depressed because plankton and algae (blanket-weed) increase rapidly at the expense of other aquatic organisms. Sensitive species such as pondweed and stonewort disappear and the water may reach a relatively stable but biologically poor state.
Agricultural activities such as poor waste storage facilities, farmers applying slurry and fertilizers during adverse weather conditions or on steeply sloping land can lead to phosphates entering the waterway. This is commonly referred to as diffuse pollution.
Phosphates stimulate the growth of phytoplankton and this makes the water cloudy, reducing the light reaching the plants that grow underwater. Increased phytoplankton also depletes the water of dissolved oxygen. Ploughing up grassland and other habitats surrounding open standing water, drainage and overgrazing can all increase the possibility of soil erosion with a consequent increase in water-borne sediments.
Discharges from water treatment works, industrial sites and septic tanks can be a source of nutrient enrichment of open standing waters.
Competition from the deliberate or accidental introduction of non-native invasive species such as zebra mussel can have a damaging effect on the native flora and fauna of open standing water.
Drainage and removal of water can result in low water levels. All fish movements and migrations depend on adequate water levels and flows and low water levels can also cause important wetland habitats, such as marshes and wet woodlands, to dry out.
Dredging and the clearance of bank side vegetation can also affect downstream water quality by increasing sediment loads and nutrient concentrations, and water quality by allowing water to flow more quickly.
It is predicted that climate change will mean drier summers and milder winters and this could have an adverse effect on some species which have adapted to the cold water.
Litter is deposited each year all around the shores of our open water. Lead shot, used in hunting, can be eaten by ducks and swans and will poison them.
Boats and jet skis can damage plants, cause waves that erode the banks and disturb breeding or feeding animals and birds.