Nutrients in transitional, coastal and marine waters in Europe

Eutrophication in marine, coastal and estuarine ecosystems is caused by human activities that enrich waters with nutrients, with harmful effects. To address this, an integrated approach to reducing nutrient inputs is taken in catchments surrounding Europe's seas. Between 1980 and 2019, nitrogen levels declined overall in the Greater North, Baltic and Celtic Seas. Trends analysis of phosphorous concentrations reflected increasing levels of phosphorus in some parts of the Baltic Sea, while levels declined overall in the Greater North Sea. Time series data were not sufficient to identify trends in other regional seas. Although progress has been made, more effort is needed, along with better monitoring to allow more comprehensive assessments.

Eutrophication in marine, coastal and estuarine ecosystems is a consequence of nutrient over-enrichment, with nitrogen and phosphorus coming from land-based sources, marine activities and atmospheric deposition, as well as fluxes from neighbouring water bodies . The resulting excessive availability of nitrogen and phosphorus accelerates the growth of microalgae and higher forms of plant life, with indirect effects on aquatic organisms and water quality.

The EU takes an integrated approach to reducing the input of nutrients to aquatic systems to reduce the risk of eutrophication and achieve good status for marine waters. EU legislation aimed at addressing this issue includes the Water Framework Directive and the Marine Strategy Framework Directive, both of which set targets in relation to nutrient levels. The Nitrates Directive and the Urban Waste Water Treatment Directive are also relevant. The EU Biodiversity Strategy to 2030 and Farm to Fork are the main policies under the EU Green Deal setting ambitious targets for the reduction of nutrients from agriculture. International initiatives and policies that outline measures aimed at reducing nutrient loads and impacts include the Regional Sea Conventions: the Oslo-Pasis Convention (OSPAR), the Helsinki Convention (Helcom), the Barcelona Convention (UNEP-MAP) and the Black Sea Convention.

In the Greater North, Baltic and Black Seas, the number of assessment areas recording significant decreasing trends in dissolved inorganic nitrogen (DIN) levels is greater than the number recording increasing trends. However, for most of the assessment areas, no significant trend is observed. For phosphorus (orthophosphate), significant increasing trends are observed in some parts of the Baltic Sea, whereas in the Greater North Sea a significant decreasing trend is observed. For both nitrogen and phosphorus, in some regional seas no clear trends can be identified because of limited time series data.

Overall, these results show some significant decreasing trends in the levels of nutrients in regional seas and areas where nutrient management strategies have been implemented. However, phosphorus concentrations are still increasing in some regional seas (e.g. the Baltic Sea) and more needs to be done to tackle this issue.

The availability of time series data for the assessment of nutrient levels varies across regional seas, with the number of time series much larger for the Baltic and Greater North Seas than for the Mediterranean and Black Seas.

DIN concentrations in Atlantic European marine waters and in the Baltic Sea have decreased in the last four decades, reflecting the effects of reductions in nutrient inputs as a consequence of EU policy implementation.

The increasing trends in phosphorus concentrations observed in some parts of the Baltic Sea are probably related to phosphorus release from sediment under anoxic conditions. Decreasing trends are observed in the Greater North Sea.

The availability of long time series data is clearly important for assessing the effectiveness of measures taken to achieve good status for Europe’s seas. Therefore, efforts should be made to increase the spatial coverage of the assessment and fill the gaps in some regional seas.

Supporting information

Definition

This indicator looks at trends in concentrations of DIN (sum of ammonium, nitrite and nitrate) and orthophosphate in the upper 10m of the water column in Europe's seas during the season of low phytoplankton growth (SLPG) for the period 1980-2019. Data were aggregated into squares of 0.01 degree × 0.01 degree for coastal stations (within 20km of the coastline) and 0.05 degree × 0.05 degree for open water stations. The SLPG was considered August-October in the Mediterranean and Black Seas, January-March in the Baltic Sea and January-February in the other regional seas. Temporal trends were estimated with the non-parametric Mann-Kendall test. Only stations with data for at least 5 years and for the last 5-year period (2015-2019) were considered. A p-value of <0.05 was considered to indicate a statistically significant trend.

Methodology

The two sources of data for this indicator are ICES and EMODNet (Chemistry data).

The procedures of data extraction, data selection and aggregation, trend analysis and plotting of results are carried out in R.

Data with bad quality flags (bad value, probably bad value) or uncertain (value in excess, uncertain value, missing value) were discarded.

For phosphorus, concentrations of orthophosphate were used. For nitrogen, DIN, as the sum of ammonium, nitrite and nitrate, was used. Units of nutrients are expressed in µmol/l.

Only data from depths of <10m were considered.

Stations are defined geographically by position, e.g. longitude and latitude in decimal degrees. The reported data do not contain reliable and consistent station identifiers and this may fragment time series. To improve the aggregation into time series, data were aggregated into squares of 0.01 degree × 0.01 degree for coastal stations (within 20km from the coastline) and 0.05 degree× 0.05 degree for open water stations. These squares can be considered ‘stations’.

Average concentrations by station and day were calculated.

To use the average annual concentrations corresponding to the SLPG, the following temporal periods were considered: August-October in the Mediterranean and Black Seas; January-March in the Baltic Sea; and January-February in the other regional seas. In this way, average SLPG values were calculated per station and year.

Temporal trends were estimated with the non-parametric Mann-Kendall test. Only stations with data for at least 5 years and from the last 5-year period (2015-2019) were considered. A p-value of <0.05 was considered to indicate a statistically significant trend. Gap filling in the time series is not necessary for trend analysis that uses the Mann-Kendall test.

Policy/environmental relevance

The EU takes an integrated approach to decreasing nutrient inputs to aquatic systems, to reduce the risk of eutrophication and achieve good status for marine waters. The most relevant pieces of EU legislation addressing these issues are the Water Framework Directive and the Marine Strategy Framework Directive (MSFD).

In particular, the Commission Decision developed under MSFD CIS, establishes, under descriptor D5 on eutrophication, a primary criterion (D5C1) to ensure that ‘nutrient concentrations are not at levels that indicate adverse eutrophication effects. Threshold values should be set to assure Good Enviornmental Status (GES) and be harmonised with the WFD. Commission Decision (EU) 2018/229 of 12 February 2018 summarises the results of the third phase of the WFD intercalibration exercise, providing different threshold values for chlorophyll-a depending on the regional sea and water typology (EU, 2018). Nevertheless, threshold values and indicators are different for different regions and water typologies and are currently still hard to implement in an assessment on the pan-European scale. Other EU directives such as the Nitrates Directive and the Urban Waste Water Treatment Directive are also related to the conrol of eutrophication, by aiming to reduce the loads and impacts of nutrients.

In addition, international initiatives and policies such as the Regional Sea Conventions — the Oslo-Paris Convention (OSPAR), the Helsinki Convention (Helcom), the Barcelona Convention (UNEP-MAP) and the Black Sea Convention — also outline measures that aim to reduce the loads and impacts of nutrients and include countries beyond the EU.

This indicator assesses trends in nutrient levels in European transitional, coastal and marine waters to provide an indication of whether measures taken to reduce the risk of eutrophication are on track to be effective. It does not provide information on whether or not policy objectives have been achieved, as threshold values (boundaries between good and bad condition) were not available for each location.

Accuracy and uncertaintiesData sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of disseminationContact

References and footnotes

EEA, 2019, 'Nutrient enrichment and eutrophication in Europe’s seas — European Environment Agency', (https://www.eea.europa.eu/publications/nutrient-enrichment-and-eutrophication-in) accessed May 12, 2022.

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EU, 2000, Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy, OJ L 327, 22.12.2000, p. 1-73.

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EU, 2008, Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive), OJ L 164, 25.6.2008, p. 19-40.

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EU, 1991, Council Directive 91/676/EEC of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources, OJ L 375, 31.12.1991, p. 1-8.

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EU, 1991, Council Directive 91/271/EEC of 21 May 1991 concerning urban waste water treatment, OJ L 135, 30.5.1991, p. 40-52.

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EC, 2020, COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONS EU Biodiversity Strategy for 2030 Bringing nature back into our lives

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EC, 2021, 'Farm to fork strategy', European Commission (https://ec.europa.eu/food/horizontal-topics/farm-fork-strategy_en) accessed December 16, 2021.

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EC, 2022, 'Our oceans, seas and coasts — The Regional Sea Conventions', European Commission (https://ec.europa.eu/environment/marine/international-cooperation/regional-sea-conventions/index_en.htm) accessed January 12, 2022.

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OSPAR Commission, 2017, Third OSPAR integrated report on the eutrophication status of the OSPAR maritime area, 2006-2014, OSPAR Thematic Assessment,

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Commission Decision (EU) 2017/848 of 17 May 2017 laying down criteria and methodological standards on good environmental status of marine waters and specifications and standardised methods for monitoring and assessment, and repealing Decision 2010/477/EU (Text with EEA relevance. ), 2017, OJ L.

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Commission Decision (EU) 2018/229 of 12 February 2018 establishing, pursuant to Directive 2000/60/EC of the European Parliament and of the Council, the values of the Member State monitoring system classifications as a result of the intercalibration exercise and repealing Commission Decision 2013/480/EU (notified under document C(2018) 696)Text with EEA relevance., 2018, OJ L.

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