Eutrophication is one of the major threats to the health of estuarine, coastal and shelf sea ecosystems around the world. It occurs when the enrichment of water by nutrients (often from fertilizer run-off from agricultural land or sewage discharges) causes an accelerated growth of algae and higher forms of plant life. This in turn leads to an undesirable disturbance to the balance of organisms present in the water and to the quality of water concerned. (This definition is based on the Urban Waste Water Treatment Directive, UWWTD; 91/271/ EEC.) For this assessment, undertaken in 2007, we focused on the risk posed by nutrient enrichment in the period 2001 to 2005 and in the near future, and the extent of eutrophication problems in UK waters.

We used OSPAR’s Comprehensive Procedure for identifying the eutrophication status of coastal and offshore waters. This uses a ‘weight of evidence’ approach to identify ‘non-problem areas’, ‘potential problem areas’ at risk of eutrophication, and ‘problem areas’ that are already experiencing undesirable disturbance to the balance of organisms. For estuarine water we used the results of similar assessments carried out in support of the EU UWWTD and Nitrates Directive. We assessed field measurements against a checklist of parameters including concentrations of nutrients, chlorophyll and dissolved oxygen, phytoplankton indicator species, macrophytes and toxin-producing algae. Figure 4.14 shows data collected using a SmartBuoy. Higher concentrations of nitrogen and silicate are seen during the winter and of chlorophyll in the spring and summer, in response to blooms of algae which consume nutrients and photosynthesise. Each dot represents a single, automatic, measurement. Traditionally, nutrients levels and trends were monitored using a relatively small number of discrete samples analysed on-board ship or in the laboratory. Newer developments allow the gathering of much more frequent data (as shown in Figure 4.14).

Figure 4.14 A time series of nitrate + nitrite (TOxN), silicate and chlorophyll concentrations (in situ data) from the Cefas SmartBuoy in Liverpool Bay, together with the results from periodic ship-based surveys (discrete).

We found that UK coastal and offshore waters in each of the eight regions are currently non-problem areas with respect to eutrophication. The coastal waters include five areas that had caused concern in an earlier assessment undertaken in 2002 and reported in Charting Progress – these were East England, East Anglia, Liverpool Bay, the Solent and the Firth of Clyde. Although these areas are still nutrient enriched, and some showed evidence of accelerated growth of algae, there was no evidence for undesirable disturbance, and the risk is not increasing.

However, in 2007 we identified 17 small estuaries and harbours as problem areas and 5 as potential problem areas. These water bodies are also designated as Sensitive Areas under the UWWTD and as Nitrate Polluted Waters (eutrophic) under the Nitrates Directive, and hence are already subject to nutrient reduction programmes. But there is such a large reservoir of nutrients in soils and sediments that the environmental response to the reduction in nutrient inputs is likely to be slow. Moreover, it is not clear to what extent these protective measures will lead to ecological recovery, because the eutrophication process is complex and may not be easily reversible.

The biggest pressures on eutrophication status occur in the east, south and north-west of England where nutrients of human origin (notably nitrate and phosphate from agriculture and urban waste water sources) have enriched coastal waters. We found no changes in eutrophication status over the period 1996 to 2005, and re-assessment of the five areas cited above with additional data confirmed them to be non-problem areas. The designation of Nitrate Vulnerable Zones covering 69% of the land in England, 14% of Scotland, 4% of Wales and the whole of Northern Ireland is likely to lead to a reduction in nutrient inputs from agriculture, as is the effective implementation of the UWWTD which will reduce nutrient inputs from waste water. Since 1998, total inputs of phosphate have declined by around 6% to 9% per year in all regions, while total inputs of dissolved inorganic nitrogen have decreased by 2% per year in the North Sea (Region 1) and the Irish Sea (Region 5).

We have high confidence in the assessments of eutrophication in most areas due to the availability of extensive datasets, and enhanced monitoring which was put in place in areas that were previously reported to be vulnerable.

In conclusion, we have reached a situation where eutrophication problems are apparent in some small estuaries, which occupy only a small percentage of our seas (< 0.2% of the area in each region, and < 0.03% overall). However, we should continue to reduce nutrient pressures through appropriate actions under EU Directives to address areas where there are still problems, even though recovery may take many years. A further application of the OSPAR Comprehensive Procedure to assess the current eutrophication status will begin shortly.