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.
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.
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.
No uncertainties have been specified.