The scientific review was commissioned by the Agriculture and Environment Departments following a threat of further legal action by the European Commission against the UK for failing to implement the 1991 Directive fully.
The ECJ held the UK to be in breach of the Directive in 2000 (ENDS Report 311, p 54 ), and continuing non-compliance may result in sizeable fines. The prospect of further legal proceedings prompted substantial additional designations of nitrate vulnerable zones (NVZs) in Britain last year within which controls on the application of nitrogen via fertilisers and manures apply.
As usual, Northern Ireland is lagging behind. It currently has just three small NVZs designated in 1999 in catchments where nitrate levels in groundwater exceeded 50mg/l. These cover 0.1% of its land area.
On 17 December, Ministers announced that there will shortly be a consultation proposing four additional small NVZs.
However, this will not be the end of the process. A second consultation was promised early in 2003 on the far-reaching conclusions drawn by the scientific review, and a stakeholder group will also be appointed to consider the implications.
The driver in this case is not the 50mg/l threshold at which NVZ designations are triggered. The Directive also requires designations where waters are already eutrophic or may soon become so if corrective action is not taken.
Until recently, it was generally believed that the eutrophication criterion applied only in marine waters, where nitrogen is the nutrient limiting the onset of eutrophication. In freshwaters, phosphate is usually perceived to be the limiting nutrient.
However, an ECJ judgement last summer in a case brought by the Commission against France has changed all that. It upheld the Commission's view that nitrogen can also stimulate the growth of algae in freshwaters, and hence that nitrogen inputs to eutrophic lakes and rivers cannot be disregarded under the Directive.
In practice, the Commission says, this means that NVZs should be designated where a water body has been shown to be eutrophic and farms contribute more than 20% of the nitrogen loading.
In Northern Ireland, nitrate levels in surface waters are generally comfortably below the 50mg/l designation threshold. But the position on eutrophication is very different. According to the scientific review, the phenomenon is "commonplace" throughout the country.
Prominent cases are the two largest freshwater lakes, Lough Neagh and Lough Erne, which drain 44% of the Province's land area. The review acknowledges that algal growths in Lough Neagh are probably limited by nitrogen during the summer months, and also suggests that "the possibility of some degree of nitrogen limitation is probable" in Lough Erne.
Smaller lakes are also affected. A survey at the end of the 1980s found that 70% out of 495 lowland lakes were eutrophic or hypereutrophic. A further survey of 100 small lakes last year confirmed that eutrophication is "widespread".
The phenomenon is also common in rivers. If an EU guide level on the phosphorus content of rivers is used then some 27% of river lengths monitored in 2000 were eutrophic. The figure rises to 74% if the tougher standard applied in the Republic of Ireland is used as the yardstick.
Finally, several major sea loughs, including Lagan, Quoile and Belfast Lough, are all eutrophic, and nitrogen is the limiting nutrient. Investigations are under way on the nutrient status of several others, including Strangford and Foyle.
Where nitrogen budgets have been studied, the case for NVZ designation appears overwhelming. Agriculture accounts for at least 76% of the nitrogen load into Lough Neagh, and 92% in Lough Erne.
Summarising their findings, the review team conclude that some 77% of major water bodies may require designation as NVZs on the basis of eutrophication. The total excludes catchments of many small lakes known to be eutrophic as well as those of rivers showing signs of nutrient enrichment.
Commenting on the findings, Agriculture Minister Ian Pearson said the question now is whether "to tackle eutrophication by further NVZ designations or by adopting action programmes for the whole of Northern Ireland." An assessment of the financial implications for farmers is to be commissioned.
That is the issue from a legal perspective. From an environmental perspective, however, the review team makes clear that reducing nitrogen inputs alone will achieve little reduction in eutrophication "unless phosphorus losses to water are controlled simultaneously."
Mr Pearson said nothing about this, but it is a question facing the whole of the UK. The Government, however, appears to be set on taking little action to tackle phosphorus inputs from farms until the end of the decade, when measures must be put in place under the EU water framework Directive so that "good ecological status" is achieved in all waters by 2015.
However, the review team is adamant that a delay of this kind will result in failure to meet that objective. "The current widespread eutrophic conditions of surface waters in Northern Ireland are the product of decades of high nutrient loadings," it notes. "It will therefore require immediate and effective action to reduce the inputs of both nitrogen and phosphorus to these waters in order to meet the obligations of the water framework Directive."