You are here: Home / Publications / Environmental signals 2000 / 13. Eutrophication

13. Eutrophication

Page Last modified 13 Apr 2011, 09:52 PM

13. Eutrophication

indicator policy issue DPSIR assessment
nitrogen and phosphorous concentrations in rivers do we see the results of nutrient policies in rivers? state /
nitrogen run-off what have been the main contributions to the total load of nitrogen? pressure
nitrogen balance has agriculture balanced its inputs and ouputs of nutrients? pressure
phosphorous load what have been the main contributions to the total load of phosphorous? pressure
discharge of phosphorous from urban wastewater treatment plants what has been the result of the urban wastewater directive and national measures? pressure
wastewater treated - " - response
nitrate concentrations in groundwater how often are groundwater quality aims for nitrogen exceeded? state
phosphorous concentrations in lakes do we see the results of a decrease in phosphorous emissions? state
phosphate concentrations in coastal water do we see the results of nutrient policies in coastal waters? state
nitrate concentrations in coastal water - " - state

Measures to reduce nutrient pollution of water bodies have been implemented with varying degrees of success. The Urban Waste Water Directive and investment by EEA member countries in nutrient removal have reduced phosphorus discharges. Nitrogen pollution has been reduced to a far lesser extent, with the nitrogen surplus from agriculture staying at the same concentration as in 1990. Phosphorus concentrations in major rivers have fallen significantly over the last 15 years, but nitrate concentrations have remained constant and high. Nitrate concentrations in many groundwater supplies exceed limits set by the Drinking Water Directive. Phosphorus concentrations in severely affected lakes have fallen significantly. Nutrient concentrations in coastal waters show little overall improvement.

13.1. What is eutrophication?

The overloading of seas, lakes, rivers and streams with nutrients (nitrogen and phosphorus) can result in a series of adverse effects known as eutrophication. Phosphorus is the key nutrient for eutrophication in fresh waters and nitrate is the key substance for salt waters.

In severe cases of eutrophication, massive blooms of algae (sessile and planktonic) occur. Some blooms are toxic. As dead algae decompose, the oxygen in the water is used up; bottom-dwelling animals die and fish either die or leave the affected area. Increased nutrient concentrations can also lead to changes in the aquatic vegetation. The unbalanced ecosystem and changed chemical composition make the water body unsuitable for recreational and other uses, and the water becomes unacceptable for human consumption. High concentrations of nitrate in drinking water are considered a human-health problem because in the stomach nitrate is converted rapidly to nitrite, which can cause a reduction in the blood’s oxygen-carrying capacity.

The main source of nitrogen pollution is run-off from agricultural land, whereas most phosphorus pollution comes from households and industry. The rapid increase in industrial production and household consumption during the 20th century has resulted in greater volumes of nutrient-rich wastewater. Nutrient removal during wastewater treatment in sewage-treatment plants is vital to minimise the impact of nitrogen and phosphorus pollution on Europe’s water bodies.

Since 1980, nitrate concentrations in major EU rivers have been about constant (Figure 13.1). There is no evidence that reduced application of nitrogen fertilisers to agricultural land has resulted in lower nitrate concentrations in rivers. The decline in phosphorus concentrations in major EU rivers is due to improved wastewater treatment and less phosphorus in household detergents.

Figure 13.1: Nitrogen and phosphorus in major EU rivers

Source: EEA-ETC/IW based on country returns under EC Exchange of Information Decision (77/795/EEC)
Note: Median of indexed values of concentrations of nitrate nitrogen and total phosphorus at 92 locations.

Nitrate concentrations have been largely unchanged since 1980.

Phosphorus concentrations in some EU rivers have fallen since the mid-1980s, particularly in the largest and most polluted rivers.

13.2. Controls of nutrient discharges

Control of point-source discharges varies between EU Member States. However, some improvement is likely as Member States invest in new infrastructure in order to comply with the Urban Waste Water Treatment Directive. This requires Member States to provide urban areas with sewage collection and wastewater treatment systems. In sensitive areas, nutrient removal is required as part of a more advanced treatment programme. Since May 1999 all Members States have fully or partly transposed this Directive into their national laws and developed implementation plans – in most cases with considerable delay. There are indications that it will be possible to reach the deadlines for achieving the environmental objectives of the Directive, although for Brussels and Milan much remains to be done.

Controls have been most effective for major point sources, such as urban wastewater and industrial effluents, and where nutrient use has been restricted or banned, e.g. phosphate in detergents. However, many small point sources are not covered effectively by current legislation and are likely to discharge into small rivers where they can have a significant negative impact.

Efficient control of diffuse sources such as nitrate run-off from agriculture has rarely been achieved. Fertiliser use and nutrient loads from manure have fallen since the 1980s, mainly due to the effects of CAP reforms. Nutrient inputs to water bodies from agriculture are still too high. Implementation of the Nitrate Directive has been unsatisfactory in most Member States and the Commission has begun legal action against those Member States that have not yet complied.

Although phosphorus pollution from point sources has fallen, it may be necessary to take measures to reduce diffuse loads from agricultural areas — particularly in areas where the soil’s absorption capacity for phosphorus is exceeded.

13.3. Nitrogen flows

Comparison of nitrogen run-off with the application of fertiliser shows that diffuse sources – particularly agriculture – dominate (Figure 13.2). Human activities account for less than half the nitrogen discharged in the Nordic countries, where about 7 % of the land is cultivated and population density is low. Most comes from run-off from forested and uncultivated areas.

Those areas with the five highest amounts of nitrogen run-off in Figure 13.2 have similar amounts (40-50 %) of arable land. The marked increase in run-off from 6.5 kg/hectare in Poland to 28 kg/hectare in western Europe is due to more intensive agriculture – as shown by the higher rates of fertiliser application.

Figure 13.2: Nitrogen run-off and fertiliser application in selected European areas, latest available year between 1988 and 1996

Source: EEA-ETC/IW
Note: All areas greater than 300 000 km2. Run-off and fertiliser application per hectare of total land area.

Agriculture is the main source of nitrate pollution. Nitrogen run-off in areas with intensive agriculture is over 5, and often more than 10 times higher, than that from forested areas.

The two main nitrogen inputs to agricultural land are mineral fertilisers and manure. Between 1990 and 1995, the total input in the first 12 EU Member States fell by around 5 % (Figure 13.3). However, there was a similar decrease in nitrogen removal by harvested crops (i.e. output). Surplus nitrogen – a source of pollution – remained almost constant at 7.2 .7.4 million tonnes. Nitrogen surpluses in EU Member States for 1990, 1993 and 1995 are shown in Table 13.1. The nitrogen balance in the 15 EU Member States is only available for 1995, but is almost identical to that for the 12 Member States included in Figure 13.3.

Figure 13.3: Nitrogen balance for agricultural soil in EU Member States, 1990-1995

Source: Eurostat
Note: Based on data from the first 12 EU Member States.

About a third of nitrogen applied to agricultural land is not removed with the harvest.

13.4. Phosphorus flows

Figure 13.4 shows that the annual phosphorus load per hectare area increases with population density. In relatively sparsely populated areas with low agricultural activity, such as the Nordic countries, only half the phosphorus loading is due to human activities. The other half comes from diffuse run-off from forested and uncultivated land. For example, in the Baltic Sea catchment area where the population density is less than 50 inhabitants/km2, the phosphorus load is 0.23 kg/hectare. In the North Sea catchment area, the population density is about 200 inhabitants/km2 and the phosphorus load is 2.7 kg/hectare.

Figure 13.4: Sources of phosphorus in selected European countries and catchment areas, latest available year between 1988 and 1996

Source: EEA-ETC/IW
Note: All areas greater than 300 000 km2.

Households and industry are the biggest contributors of phosphorus to the environment. However, in those parts of Europe with intensive agriculture, the contribution from agriculture approaches 50 % of the total.

Over the past 15 years, phosphorus discharges from urban wastewater treatment plants in many countries in north-west Europe have fallen by 50-80 % (Figure 13.5). The main reason for this reduction is the upgrading of wastewater treatment plants to include phosphorus removal. The shift to phosphate-free detergents has also contributed.

Figure 13.5: Discharge of phosphorus from urban wastewater treatment plants in north-west Europe

Source: EEA-ETC/IW
Note: Data from Denmark, Finland, the Netherlands, Norway, Sweden and North Rhine–Westphalia (Germany).

Total phosphorus discharges from urban wastewater treatment plants in north-west European countries have fallen significantly during the past 15 years.

During the same period, marked changes have occurred both in the proportion of the population connected to the sewerage system and in wastewater treatment technologies (Figure 13.6). In northern and central European countries, most of the population was connected to the sewerage system and a wastewater treatment plant by the early 1980s. In southern countries, the population connected to sewers has increased significantly – but by 1995 only about half had their wastewater treated.

In the 1980s, secondary treatment (i.e. biological removal of oxygen-consuming substances) became common in western countries. However, countries like Finland and Sweden were already using tertiary treatment (i.e. nutrient removal) as well. Many western European countries built treatment plants with nutrient removal in the late 1980s and the 1990s.

Figure 13.6: Developments in wastewater treatment in European regions between 1980-85 and 1990-95

Source: Eurostat and national information
Notes: Nordic: Finland, Iceland, Norway and Sweden. EEA Central: Austria, Denmark, Germany, Ireland, Luxembourg, the Netherlands and the UK. EEA South: Greece and Spain.

Nordic and central European countries have the highest percentage of wastewater subject to tertiary treatment (particularly phosphorus removal).

13.5. Nutrients in ground and surface waters

13.5.1. Nitrate in groundwater
When nitrate is washed out of agricultural soil, it first contaminates shallow groundwater. At a later stage, deeper groundwater in vulnerable positions is affected, e.g. parts of the UK with fractured limestone with thin soil cover and the eastern Netherlands with its sandy soils and severe nitrogen loading. Most groundwater supplies in the EU are from deep wells and are therefore not immediately affected by high nitrate concentrations. In areas where the nitrogen concentrations in groundwater are high and the water is obtained from shallow groundwater sources (the usual practice for private and small communal supplies), the population can be at risk.

Figure 13.7 shows that the Drinking Water Directive guideline value of 25 mg nitrate/litre for drinking water is exceeded at over half the groundwater sampling sites used in the compilation of two EEA databases. The maximum allowable concentration (MAC) is exceeded at around a quarter of the sampling sites.

Figure 13.7: Nitrate concentrations in groundwater, latest available year between 1990 and 1996

Source: EEA-ETC/IW
Notes: Percentage of groundwater bodies where the guide value and the MAC are exceeded: very frequently (>50 % of sites); frequently (>25 %); rarely (0–25 %); and not at all. Numbers in brackets indicate the number of administrative authorities responsible for the groundwater bodies in the database.

The Drinking Water Directive guideline value and the maximum allowable concentration for nitrate in drinking water are exceeded in many EU groundwater supplies.

13.5.2. Phosphorus in lakes
Like rivers (Figure 13.1), phosphorus concentrations in many lakes have fallen (Figure 13.8). This is particularly true for lakes that had high concentration in the early 1980s. The improvement is due to better wastewater treatment and use of phosphate-free detergents. Diverting wastewater away from the lake is another frequently used method of reducing external loading.

Despite considerable reduction in phosphorus inputs from point sources, many lakes have not yet shown the expected environmental improvement. The main reason for this is accumulation and release of phosphorus from the lake bottom or continued contamination from scattered dwellings and agricultural sources.

Figure 13.8: Phosphorus in lakes

Source: EEA- ETC/IW
Note: Number of lakes: Finland 71; Denmark 13; Ireland 6; Sweden 6; Austria 5; Germany 5; France 4; Norway 4; the Netherlands 2.

Lakes that had high phosphorus concentrations (>50 µg/litre) in the early 1980s have lower concentrations today. However, only slight changes in phosphorus concentrations have been observed in less-affected lakes.

Fishing for clean water

In cases of eutrophication, depth of visibility is one of the best indicators of lake condition. Shallow healthy lakes should have plants growing on the lake bottom, providing refuge for animal plankton from fish. The animal plankton keep plant plankton under control, thus preventing the harmful algal blooms characteristic of eutrophication. To become established and survive, however, underwater plants need high water clarity.

In Denmark, Lake Væng still showed the symptoms of severe eutrophication in 1986 despite a 63 % reduction in phosphorus inputs from 1982. Between 1986 and 1988, half the population of fish feeding on animal plankton were caught. This manipulation of the food chain resulted in an increase in the numbers of animal plankton grazing on the plant plankton and a corresponding decrease in plant plankton. Water visibility improved as the plant plankton were kept under control, leading to the establishment of underwater plants. The amount of plant plankton in the lake has remained low and stable, indicating a sustainable and clean lake environment with fewer signs of eutrophication than before the fish were removed.

Source: EEA, 1999c

13.6. Phosphorus in coastal waters

All signatories to the Third International Conferences on the Protection of the North Sea achieved the Conferences’ objective of reducing phosphorus inputs to surface waters by 50 % between 1985 and 1995 (Andersen and Niilonen, 1995). However, this reduction is not yet reflected in overall phosphate concentrations in coastal waters.

In most coastal waters, there has been zero or limited change in phosphate concentration (Figure 13.9, 13.10). However, the reduced phosphate content of detergents and other measures in the catchment area have resulted in a fall in phosphate concentrations in parts of the coastal zones in some regions, e.g. the Skagerrak,Kattegat, the German Bight and the Dutch coastal zone. The average decrease in phosphate concentration of 46 % in these areas reflects the reduction in inputs. Reduced phosphorus loads in the River Rhine have resulted in an average 50 % reduction in concentrations in the Dutch coastal zone since 1985 and less phytoplankton biomass. Present phosphate concentrations in the area are still 2 .3 times higher than marine background concentrations (De Vries et al, 1998). In the Gulf of Finland, leaching from sediment has caused phosphate concentrations to increase recently. In general, the presence of a large buffer of phosphorus in coastal sediments is the main reason why the reduction in phosphate inputs has not been reflected immediately by a reduction in phosphate concentrations.

Figure 13.9: Changes in phosphate concentration in OSPAR and HELCOM coastal waters, 1985-1998

Source: ICES; Finnish National Focal Point
Notes: Trend in winter phosphate concentrations expressed as a percentage of squares (10×10 km) in coastal waters of OSPAR and HELCOM countries within the EU and Norway. The total number of squares in each area is given in brackets. The category 'no/limited trend' indicates a trend between +10 % and -10 %. The methodology for the aggregation of squares in each region in given by Van Buuren et al. (draft)

Most coastal waters show little or no change in phosphate concentrations. However, there is a substantial decrease in 35 % of OSPAR and HELCOM coastal waters within the EU and Norway.

Figure 13.10: Nitrate and phosphate concentrations in Atlantic, North Sea and Baltic coastal waters, 1985-1996

13.7. Nitrogen in coastal waters

No signatory state to the Third International Conferences on the Protection of the North Sea achieved the Conferences’ objective of reducing nitrogen inputs to surface waters by 50 % between 1985 and 1995. However, all North Sea States are expected to have reached a substantial reduction of nitrogen inputs to surface waters of around 25 % (Andersen and Niilonen, 1995).

Figure 13.11 shows a gradual reduction in nitrate concentrations in coastal waters for 48 % of the 10 km2 squares in each sub-region. A 100 % decrease was found only in sub-regions with up to three squares per sub-region; this might therefore be due to the limited data available. The mean decrease in nitrate concentration is around 25 %. Part of the decrease appears to be due to very low run-off into rivers in 1996 and 1997.

About 20 % of the squares in each sub-region show an increase in nitrogen concentration. These are mainly sub-regions of the Baltic Sea, Kattegat and Skagerrak, where the increased nitrate concentrations are probably related to internal fluxes (remineralisation of nitrogen).

Figure 13.11: Changes in nitrate concentration in OSPAR and HELCOM coastal waters, 1985-1998

Source: ICES; Finnish National Focal Point
Notes: Trend in winter nitrate concentrations expressed as a percentage of squares (10×10 km) in coastal waters of OSPAR and HELCOM countries within the EU and Norway. The total number of squares in each area is given in brackets. The category 'no/limited trend' indicates a trend between +10 % and -10 %. The methodology for the aggregation of squares in each region in given by Van Buuren et al. (draft)

Nitrate concentrations in coastal waters fell in nearly half OSPAR and HELCOM coastal waters within the EU and Norway between 1985 and 1998. However, there were also some increases.

13.8. Indicator improvement

An ideal pressure indicator for eutrophication would be the total emissions of nutrients to waters and to the atmosphere by country and by source (point and diffuse). OSPARCOM is developing guidelines for the measurement and calculation of such emission data for nutrients.

When fully implemented, the EEA’s water information and monitoring network, Eurowaternet, will provide information on water quality and quantity issues for different types of water bodies. Information will also be gathered on the status and trends in the quality and quantity of Europe’s inland water resources and how these relate and respond to driving forces and pressures on the environment.

For the future, impact indicators on eutrophication (e.g. algae blooms, oxygen deficiency, changes in macrophyte and bottom animal communities) should be developed. Also indicators and analysis of the effectiveness of response measures such as the Urban Waste Water Treatment Directive and the Nitrates Directive against the costs of implementation, will be needed.

Table 13.1: Nitrogen surplus in agricultural areas of EU Member States, 1990-1995
Unit: kg nitrogen/ha utilised agricultural area (UAA)
  1990 1993 1995
Austria     16
Belgium 106 109 103
Denmark 93 92 72
Finland     51
France 47 54 57
Germany 105 101 102
Greece 84 61 58
Ireland 47 60 62
Italy 62 83 76
Luxembourg 124 124 121
Netherlands 229 212 213
Portugal 27 23 22
Spain 40 37 37
Sweden     38
UK 40 39 40
EU 12/15 60 60 60
Source: Eurostat

Note: Surplus calculated as balance of inputs (mineral fertilisers, manure, biological fixation and atmospheric deposition) and outputs (harvested crops). Total average in EU 12 given for 1990 and 1993, and for EU 15 for 1995.

13.9. References and further reading

Andersen, J. and Niilonen, T. Eds. 1995. Progress report. Fourth international conference on the protection of the North Sea. Ministry of the Environment and Energy, Danish Environmental Protection Agency, Copenhagen.

Borum, J. 1996. ‘Shallow waters and land/sea boundaries’ in Eutrophication in Coastal Marine Ecosystems. Eds: B.B. Jørgensen and K. Richardson. American Geophysical Union. pp. 179-205.

De Vries, I., Duin, R.N.M., Peeters, J.C.H., Los, F.J., Bokhorst, M. and Laane. R.W.P.M. 1998. ‘Patterns and trends in nutrients and phytoplankton in Dutch coastal waters: comparison of time-series analysis, ecological model simulation and mesocosm experiments.’ In ICES Journal of Marine Science Vol.55, pp. 620-634.

EEA (1999a). Groundwater quality and quantity in Europe. Environmental assessment report No 3. European Environment Agency, Copenhagen.

EEA (1999b). Environment in the European Union at the turn of the century. Environmental assessment report No 2. European Environment Agency, Copenhagen.

EEA (1999c). Nutrients in European ecosystems. Environmental assessment report No 4. European Environment Agency, Copenhagen.

HELCOM (1996). Third periodic assessment of the state of the marine environment of the Baltic Sea 1989-1993.Balt. Sea Environ. Proc. No. 64 B.

HELCOM. The state of the Baltic marine environment.

Van Buuren, J., Smit, T., Poot. G., and van Elteren, A. (draft). Testing of indicators for the marine and coastal environment in Europe. The development of the ETC/MCE indicator database. European Environment Agency technical report, Copenhagen.

European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Phone: +45 3336 7100