Eutrophication or over-enrichment of fresh and coastal waters is recognised as a threat to the health and diversity of ecosystems. Nuisance blooms of algae, toxic tides and scums and the loss of species of importance for conservation are being increasingly blamed on excessive levels of phosphorus and nitrogen.
WWF's report sets out the extent of eutrophication around the UK and its likely environmental impacts. Although the UK has signed up to EU and international agreements to limit nutrient inputs, the report says that progress has been slow and faltering.
The effects of coastal eutrophication include increased growth of seaweeds. An example is the proliferation of mats of sea lettuce on intertidal mudflats which may hamper wading birds that feed on invertebrates. One such case is the Ythan estuary in eastern Scotland, designated as a nitrate vulnerable zone last year (ENDS Report 303, p 39 ).
The report also points to increased dumping of foul-smelling masses of seaweed along the strand line, resulting in loss of amenity and higher clean-up costs for local authorities.
Changes in nutrient levels may alter the abundance of species and have knock-on effects for other wildlife. There may have been a decline in certain seaweed species, the report notes, but perhaps the most notable effect has been the decline in eelgrass.
Eelgrass beds were once abundant around the UK coast, helping to provide protection against erosion. They are also an important habitat for species like seahorses, pipefish and cuttlefish and commercially important sea bass and grey mullet.
The three kinds of eelgrass around the UK have been in decline for 50 years due to a wasting disease which appears to be promoted by high nutrient levels. Only 20 of 155 estuaries now possess eelgrass beds larger than one hectare in size, WWF says - an 85% decline since the 1920s. It concludes that eelgrass "now demands the highest level of protection and restorative measures, and the avoidance of eutrophication must be an important part of that strategy."
Eutrophication also alters the abundance of smaller marine algae such as the sewage-like Phaeocystis - which commonly appears around the coast in summer. Toxic species such as Alexandrium andGymnodinium , which poison shellfish and kill wildlife and farmed fish, appear to be a growing problem. It is "not credible", the report says, "to assert without doubt that current levels of toxic and other harmful blooms are purely natural."
The report reviews the UK's faltering commitment to reducing marine eutrophication in recent years. It chose not to implement a 1987 Ospar target to reduce inputs of nitrogen and phosphorus to the North Sea by 50%.
However, the UK is bound by the 1988 Ospar eutrophication strategy, which incorporates the source-based 50% goal of reducing nutrient inputs. It also includes a target-based approach based on ecological quality objectives to protect particular sites. It requires the eutrophication status of all coasts and estuaries to be established and ecological quality objectives set by 2002.
The goal is to achieve a healthy marine environment "where eutrophication does not occur by 2010". If the UK is to comply, WWF believes that there will need to be substantial new investment in nutrient removal during the water industry's 2005-2009 investment period. Other industries such as food and drink might also be required to cut nutrient discharges, and a new drive will be needed to reduce diffuse nutrient inputs from agriculture.
Two weeks later, blooms were detected off Orkney and the north-west of the Scottish mainland. Hundreds of thousands of fish died at farms in the Torridon and Skye areas, but some of these were later blamed on larval jellyfish mixed in with the algae. The invertebrates have poisonous stings and can suffocate fish by blocking their gills.
The cause of such blooms is controversial. They appear in warm and settled weather, and some experts believe they are becoming more frequent and are exacerbated by nitrate inputs via rain and coastal discharges (ENDS Report 295, p 12 ).