Phosphate is the most important factor causing freshwater eutrophication - nutrient enrichment leading to algal blooms, oxygen depletion and a decline in amenity and conservation value. The main sources of phosphate are sewage discharges and diffuse inputs from agricultural land.
The Department of the Environment (DoE) has long maintained that eutrophication is a problem in only a few waters such as the Norfolk Broads. But there is increasing support for the view that it is common in well populated and intensively farmed areas.
Last year, a leading academic averred that eutrophication is an "extremely widespread problem" affecting nature conservation, public amenity and water supply (ENDS Report 252, pp 3-5 ). And a survey sponsored by the former National Rivers Authority (NRA) found that 23% of lakes are severely affected by eutrophication (ENDS Report 258, pp 8-9 ).
English Nature, the statutory nature conservation agency, has spoken out recently on the need to protect aquatic wildlife sites from eutrophication. Target phosphate levels for conservation sites are between 2.5 and 11 times lower than current average levels in rivers (ENDS Report 266, p 12 ).
Despite the increasing weight of evidence, there has been little action on eutrophication other than limited measures required by the 1991 EC Directive on urban wastewater treatment. The action announced by the European Commission against Ireland last December was a surprise for the DoE because it is being taken under another Directive whose implications for eutrophication appear not to have been considered.
The 1976 Directive on discharges of dangerous substances requires Member States to set WQOs for "grey list" substances, including phosphate. WQOs have been set in Britain for some metals and organic compounds, but not for phosphate.
A spokeswoman for the Commission said that it will be asking other Member States about phosphate controls. Denmark, the Netherlands and Germany have either set or are developing objectives. Ireland is now doing so in response to the Commission's action.
A spokesman for the Irish DoE said that it expects shortly to receive a "reasoned opinion" from the Commission - the penultimate step in the EC's infringement procedure which may result in proceedings before the European Court of Justice. The action is believed to have been triggered by a complaint from angling groups about the deteriorating quality of some game fisheries. Recent surveys have confirmed that some of the country's best salmon rivers and lakes are becoming enriched with phosphorus.
The legal action has prompted the Irish DoE to develop a eutrophication strategy.1 Published in May, its key proposals are WQOs for phosphate in rivers and lakes, interim and long-term phosphate targets for eutrophic waters, the designation of sensitive areas under the wastewater treatment Directive, and nutrient management plans for farms. Limits on the phosphate content of detergents are also being considered.
Inputs of phosphate from agriculture are particularly important in much of Ireland. The strategy proposes that farmers measure the phosphate content of soils and integrate manure and fertiliser use to avoid a phosphate build-up. Soil phosphorus levels have increased ten-fold since 1950, and the strategy estimates that farmers could save £25 million annually by cutting back on phosphate fertilisers.
In the UK, the Environment Agency inherited a draft eutrophication strategy from the NRA. A revised draft is undergoing "internal consultation", a spokesman said, and should be passed to the DoE shortly.
Apart from the threat of legal action by the Commission, another major driving force for action on eutrophication is the negotiations between the Agency, the water industry and Ofwat on water companies' investment plans for 2000-5. Any requirement for additional phosphate stripping at sewage works will need to be included in their plans (see pp 40-41 ).
Phosphate stripping has already been required at 41 sewage works discharging into 29 waters designated as "sensitive areas" under the 1991 Directive. This requires works serving population equivalents of more than 10,000 and discharging to "sensitive areas" to remove phosphate unless it is shown that this would have no impact on eutrophication.
However, phosphate removal may be needed at many more sewage works following the first four-year review of designations under the Directive. The Agency is currently considering the case for designating about 150 additional waters as "sensitive areas".
A recent Agency study found that 90% of the phosphate inputs to the lower Thames come from sewage effluent.2 Whether phosphate stripping will now be required at all 67 of the major sewage works discharging to the river will depending on the extent to which each is deemed to affect its eutrophication status. A spokesman said that while there was a presumption in favour of phosphate removal, the Agency will be considering indices of eutrophication upstream and downstream of each discharge. Phosphate removal will not necessarily be sought where discharges produce no detectable deterioration in flora, fauna or chlorophyll levels.