Eutrophic standing waters are nutrient-rich, naturally or through artificial enrichment. They are characteristically green in colour due to the dense populations of algae.
- Site: Nutrient-enriched, anaerobic mud
- Main species: Algae
- UK: 1785 km2
- NI: 940 km2
- Eutrophic standing waters are rich in plant nutrients & are characterised by algae populations in mid-summer.
- The beds are typically composed of dark anaerobic mud that has high organic matter content.
- Water bodies such as lakes, reservoirs, gravel pits may become eutrophic through natural or artificial enrichment (e.g. input of fertilisers).
- Nitrogen & phosphate, which are required for plant growth, are present in high concentrations from natural or artificial sources. Inorganic nitrogen & total phosphorus are the main indicators of the nutrient content of lakes. Eutrophic standing waters have nutrient levels of >0.035 mg 1-1 total phosphorus & >0.5mg 1-1 total inorganic nitrogen.
- Characteristic plant species vary with the area, nutrient levels & exposure. They include duckweeds Lemna spp., white water-lily Mymphaea alba, yellow water-lily Nuphar lutea & spiked water-milfoil Myriophyllum spicatum.
Current Status in UK & Northern Ireland
- A large proportion (72%) of lakes in Northern Ireland have a surface area of <2 ha, representing only 1.2% of the total water surface. In NI lakes cover approximately 4.5% of the total surface area.
- There is an estimated 1785 km2 of eutrophic standing water in the UK (UK Biodiversity Steering Group, 1998)
- Northern Ireland contains a high proportion (>52%) of the UK resource, especially in the east & west lowlands (NIBG, 2000). The EHS estimated that eutrophic standing water covers 940 km2 in NI.
- The largest eutrophic standing waters in Northern Ireland are Lough Neagh & Lough Beg & Upper Lough Erne.
- Eutrophic standing waters are under considerable pressure from human activities, which may reduce their biodiversity. Threats include:
– Agricultural practices may pollute water bodies through inappropriate application of slurry or inorganic fertilisers.
– Eutrophication is a considerable concern in Northern Ireland waters, which occurs due to the release of nutrients, particularly phosphorus. This stimulates excess phytoplankton growth, which results in a cloudy underwater environment & submerged plants do not receive sufficient sunlight.
– Drainage & water removal can result in low water levels, which can cause drying out of important wetland habitats & prevent fish from spawning.
– Dredging & bank side vegetation clearance may increase suspended sediment & nutrient concentrations.
– Invasive species, such as the Zebra mussel, can negatively affect native species by direct competition and/or altering the natural habitat.
– Recreational activities (e.g. boating) can damage aquatic plants & disturb bird populations.
– Fish farms on rivers may release waste & partly decomposed food into natural waterways, which may lead to enrichment, increased suspended solids & decreased oxygen levels.