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Indicator Assessment
Winter oxidized nitrogen (NO2 + NO3) concentrations in European seas in 2010
Note: The map shows the winter oxidized nitrogen concentrations in the European coastal and open waters in 2010. The low category refers to values within the lowest 20th percentile and the high category refers to values within the upper 20th percentile of concentrations in a regional sea
Winter orthophosphate concentrations in European seas in 2010
Note: The map shows the winter orthophosphate concentrations in the European coastal and open waters in 2010. The low category refers to values within the lowest 20th percentile and the high category refers to values within the upper 20th percentile of concentrations in a regional sea.
Trend in winter oxidized nitrogen concentrations in coastal and open waters of the Baltic, North East Atlantic (Greater North Sea, Celtic Seas) and Mediterranean Sea (Adriatic Sea), 1985 - 2010
Note: The figure shows trend in winter oxidized nitrogen (nitrate + nitrite) concentrations in coastal and open waters of the Baltic, North East Atlantic (Greater North Sea, Celtic Seas) and Mediterranean Sea (Adriatic Sea) (% of stations showing a statistically significant change within the period 1985-2010). Numbers in parentheses indicate the number of stations included in the analysis for each country. "Open sea" is the total of all off-shore stations (>20km) within a (sub)region.
Trend in winter orthophosphate concentrations in coastal and open waters of the Baltic, North East Atlantic (Greater North Sea, Celtic Seas, Bay of Biscay), and Mediterranean Sea (Western Mediterranean Sea, Adriatic Sea), 1985 - 2010
Note: The figure shows trend in winter orthophosphate concentrations in coastal and open waters of the Baltic, North East Atlantic (Greater North Sea, Celtic Seas, Bay of Biscay), and Mediterranean Sea (Western Mediterranean Sea, Adriatic Sea) (% of stations showing a statistically significant change within the period 1985-2010). Numbers in parentheses indicate the number of stations included in the analysis for each country. "Open sea" is the total of all off-shore stations (>20km) within a (sub)region.
Observed changes in winter oxidised nitrogen (NO2 and NO3) concentrations, 1985–2010
Note: The map shows stations with a statistically significant decrease (green), increase (red) or no trend (yellow) in winter oxidised nitrogen concentrations within the period 1985-2010. Selected stations must have at least data in the period from 2007 to present and at least 5 years data in all.
Observed changes in winter orthophosphate (PO4) concentrations, 1985–2010
Note: The map shows stations with a statistically significant decrease (green), increase (red) or no trend (yellow) in winter ortophosphate concentrationswithin the period 1985-2010. Selected stations must have at least data in the period from 2007 to present and at least 5 years data in all.
In 2010, the highest oxidized nitrogen (nitrate+nitrite) concentrations (> 8.7 µmol/l) and orthophosphate concentrations (> 0.76 µmol/l) were predominantly observed in coastal waters, such as in the Gulf of Finland, Gulf of Bothnia, Lithuanian coastal waters, Gulf of Gdansk and the southern coastal waters of the Bornholm Basin (Figures 1 and 2). Low concentrations of nitrogen (< 3.7 µmol/l) were measured mostly in the southern Baltic Sea, whereas low phosphate concentrations (< 0.32 µmol/l) were commonly observed in the Bothnian Bay.
Between 1985 and 2010, oxidised nitrogen concentrations decreased in 19% of the monitoring stations in the Baltic Sea and increased in 3% of the stations (Figure 3). Decreasing trends were detected especially in the open waters of the Gulf of Bothnia, Baltic Proper, Germany and Denmark (Figure 5), whereas the only increasing trend for this regional sea was observed within coastal waters of Finland.
Orthophosphate concentrations decreased in 5% of the stations and increased in 10% of the stations (Figure 4). Increasing orthophosphate trends were mainly detected in Finnish coastal waters (Gulf of Finland and Gulf of Bothnia) and in open waters of the Baltic Proper. Decreasing trends were observed mainly in Lithuanian and German coastal waters (Figure 6).
In the Greater North Sea, the highest winter oxidized nitrogen concentrations (> 46.4 µmol/l) and orthophosphate concentrations (> 1.31 µmol/l) in 2010 were observed in Belgian, Dutch and German transitional and coastal waters (Figures 1 & 2).
Long term time series indicate that oxidized nitrogen decreased in 13% of the stations (Figure 3), and orthophosphate concentrations decreased in 28% of the Greater North Sea stations (Figure 4). None of the stations showed an increasing trend in oxidized nitrogen, and only two stations showed an increasing trend in orthophosphate concentrations (Figure 5, 6). This positive development in nutrient reduction, in particular in phosphorus can be attributed to improved waste water treatment, which led to a 50 % reduction of phosphorus loading in most North Sea countries in the period 1985-2005 (OSPAR 2008).
In 2010, measurements of oxidized nitrogen concentrations in the Celtic Seas were only available from Irish and British coastal waters (Figure 1). High concentrations of orthophosphate (> 0.92 µmol/l) were observed in coastal waters in Ireland (Figure 2). In the Bay of Biscay and Iberian Coast, data for oxidized nitrogen concentrations were limited to some stations along the northern coast of Spain (Figures 1), therefore not significant to make an assessment for this sub-region. As for orthophosphate concentrations (Figure 2), most stations where data was available showed moderate to high concentrations.
In the Celtic Seas, the time series of oxidised nitrogen and orthophosphate concentrations showed no remarkable trends, but in general the time series were relatively short (< 10 years). However five stations in the Irish coastal waters (8%) showed a significantly increasing trend in orthophosphate concentration (Figure 4, 6). For the Bay of Biscay and the Iberian coast, not enough time series data were available for this sub-region to calculate trends.
As limited data are available, the assessments for the subregional Mediterranean seas are combinned. Data for 2010 consisted only of Croatian and French coastal observations and from one location in Cyprus for orthophosphate (Figures 1 & 2). High orthophosphate concentrations (>0.14 μmol/l) are observed at stations near the coast in the Gulf of Lyon and the Gulf of Ajaccio. High oxidised nitrogen (>4.3 μmol/l) concentrations are observed at near-coastal stations in Croatian waters.
Based on the current dataset, only a few notable changes in nutrient concentrations were detected. In four of the Croatian monitoring stations, an increasing trend in oxidised nitrogen concentrations was found. Generally orthophosphate concentrations did not show clear trends, except for a decreasing trend in one Croatian station (Figures 3 & 4).
It should be noted that in spite of the oligotrophic nature of the Mediterranean, meaning it is generally characterized by low concentrations of nutrients and low primary productivity, excessive nutrients are anyhow considered a major pollution problem in many of its developed coastal areas (UNEP/MAP 2007, UNEP/MAP, 2012). According to the recent initial integrated assessment by UNEP/MAP (2012), nutrient over-enrichment, possibly leading to eutrophication and hypoxia, are among the pressures and impacts that are common to all four subregions in the Mediterranean (Western Mediterranean, Central Mediterranean and Ionian, Adriatic Sea, Eastern Mediterranean).
The lack of data for this region does not allow showing annual concentrations or calculating trends.
The indicator shows 1) annual winter concentrations (micromol/l); 2) classification of concentration levels (i.e. low, moderate, high) and 3) trends in winter oxidised nitrogen (nitrate + nitrite) and phosphate concentration (micromol/l)in the regional seas of Europe.
Levels and trends of winter concentrations of dissolved inorganic nutrients are used for this indicator, as it is assumed that winter concentrations are not significantly reduced due to uptake by primary producers.
The winter period is defined as follows:
The used regional and subregional seas of Europe are in line with the geographical regions and sub-regions specified in the Marine Strategy Framework Directive (MSFD). Other European Seas (Icelandic Sea, The Norwegian Sea, the Barents Sea and the White Sea) are not covered in this indicator due to current lack of data.
Concentrations in micromol/l
Measures to reduce the adverse effects of excess anthropogenic inputs of nutrients and protect the coastal and marine environment are being taken as a result of various initiatives at all levels - global, European, regional (i.e. through Regional Sea Conventions and/or regional Ministerial Conferences), and national.
There are a number of EU Directives aimed at reducing the loads and impacts of nutrients, including the Nitrates Directive (91/676/EEC) - aimed at the protection of waters against pollution caused by nitrates from agricultural sources; the Urban Waste Water Treatment Directive (91/271/EEC) - aimed at reducing pollution from sewage treatment works and from certain industries; the Integrated Pollution Prevention and Control Directive (96/61/EEC) - aimed at controlling and preventing pollution of water from industry; the Water Framework Directive (2000/60/EC) - which requires the achievement of good ecological status or good ecological potential of transitional and coastal waters across the EU by 2015 and the Marine Strategy Framework Directive (2008/56/EC) which requires the achievement or maintenance of good environmental status in European seas by the year 2020 at the latest, through the adoption of national marine strategies based on 11 qualitative descriptors.
Additional measures arise from international initiatives and policies including: the UN Global Programme of Action for the Protection of the Marine environment against Land-Based Activities; the Mediterranean Action Plan (MAP) 1975; the Helsinki Convention 1992 (HELCOM); the OSPAR Convention 1998; and the Black Sea Environmental Programme (BSEP) 1993.
The most pertinent EU target with regard to concentrations of nutrients in water arises from the implementation of the Water Framework Directive, where one of the environmental objectives is to achieve good ecological status. Member States have defined water-type specific environmental standards to support the achievement of good ecological status.
As natural and background concentrations of nutrients vary between and within the regional seas, and between types of coastal water bodies, nutrient targets or thresholds for achieving good ecological status have to be determined while taking into account local conditions.
Within the scope of the Marine Strategy Framework Directive, nutrient levels (nutrient concentrations in the water column and nutrient ratios for nitrogen, phosphorus and silica, where appropriate), are the relevant criteria and indicators in marine waters under Descriptor 5: Human-induced eutrophication. The assessment of eutrophication in marine waters needs to combine information on nutrient levels as well as a range of ecologically relevant primary effects and secondary effects, taking into account relevant temporal scales. The nutrient targets and thresholds for achieving good environmental status are expected to be defined by 2013.
Other relevant regional targets related to nutrient pollution are:
The data used in this indicator is part of the WISE - State of the Environment (SoE) data, available in Waterbase - TCM (Transitional, Coastal and Marine) waters. Waterbase is the generic name given to EEA´s database on status, quality and quantity of Europe´s water resources. Waterbase – TCM waters contains data collected both from EEA member countries (i.e. belonging to the EIONET) and from the Regional Seas Conventions through the WISE-SoE TCM data collection process (WISE-SoE was formerly known as Eionet-Water and Eurowaternet). The resulting WISE SoE TCM dataset is therefore made of sub-samples of national data assembled for the purpose of providing comparable indicators of state and impact of transitional, coastal and marine waters () on a Europe-wide scale.
Levels and trends of winter concentrations of dissolved inorganic nutrients are used for this indicator, as it is assumed that winter concentrations are not significantly reduced due to uptake by primary producers.
Annual winter concentrations of Nitrogen and Phosphate, and classification of concentration levels
The primary aggregation consists of:
1. Identifying stations and assigning them to countries and sea regions
All geographical positions defined in the data are assigned to a sea region by coordinates. The used regional and subregional seas of Europe are in line with the geographical regions and sub-regions specified in the Marine Strategy Framework Directive (MSFD) (see below). Other European Seas (Icelandic Sea, The Norwegian Sea, the Barents Sea and the White Sea) are not covered by this indicator due to current lack of data. Also, because of the limited amount of data, only the following (sub)regions are distinguished in the maps: Baltic Sea, Celtic Seas, Greater North Sea, Bay of Biscay and Iberian coast, Mediterranean Sea, Black Sea.
| Regional Sea | Subregional Sea |
|---|---|
| Baltic Sea | None |
|
North East Atlantic Ocean |
Greater North Sea Celtic Seas Bay of Biscay and the Iberian coast Macaronesian region |
| Mediterranean Sea |
Western Mediterranean Sea Adriatic Sea Ionian Sea and Central Mediterranean Aegan - Levantine Sea |
| Black Sea | none |
The stations are then further classified as coastal or off-shore (>20 km from coast) by checking them against the coastal contour. Off-shore stations – open seas - are distinguished per sub-regional sea, whereas coastal stations are further attributed to country. These classifications are done in ArcView. Smaller regions within the regional and sub-regional seas described above are used in the aggregation process of different determinants.
EIONET stations
WISE SoE TCM data reported directly from countries are assigned to station identifiers (i.e. EIONET stations) that are listed with coordinates. For these data, which are mostly along the coast of the reporting country, stations are kept as defined.
Regional Seas Conventions data
For the data reported through the Regional Sea Conventions (and assembled by ICES), there are no consistent station identifiers available in the reported data, only geographical positions (latitude/longitude). The reported coordinates for what is intended to be the same station may vary between visits, because the exact achieved position is recorded, not the target position. Identifying station on exact position may therefore fragment time series too much.
Furthermore, duplicates between Eionet and RSC data may occur for coastal stations. A visual inspection of coastal data (< 20 km from shoreline) is therefore needed to eliminate these duplicates. For the open waters (>20 km from shoreline) coordinates are rounded to 2 decimals, and this is used to create stations (i.e. for the purpose of establishing time series) with station names derived from rounded coordinates. As coordinates for the stations are used averages over visits to the station, rather than the rounded coordinates. This ensures that in cases where most observations are in a tight cluster within the rounding area, a position within the cluster is used. The open water observations are not assigned to countries, but listed as belonging to 'Open waters' in the Country column, without reference to country.
For the coastal ICES stations, there may be overlap with Eionet stations, and for the stations close to the coast, rounding coordinates to 2. decimal may be too much (about 500 m to 1 km). However, in this update, the rounding is done also for coastal stations, but the grouping of observations to rounded coordinates is done only within observations from each country separately, and the originator country is listed. Note that these stations are not necessarily close to the coast of the originator country.
2. Annual concentration of N and P per station
The statistical aggregation for calculating annual concentrations for Nitrogen (i.e. Nitrates, Nitrites and Total Oxidised Nitrogen) and Phosphate (i.e. Orthophosphates) is done in two- or three-stage query sequences, which include:
The basic data consists of two tables:
| Measurement values table |
|---|
| WaterbaseID (Country and Station) |
| Date (Year, Month and Day) |
| SampleDepth |
| SampleID |
| Determinant, with Determinant codes "Nitrate", "Nitrite", "Total oxidised nitrogen" and "Orthophosphate". |
| Stations table |
|---|
| Unique identifier: data provider, Country and Station ID |
| Position |
| Sea region (Atlantic, North Sea, Baltic, Mediterranean and the Black Sea) |
The two tables are combined in a query which joins data to stations, linked by WaterbaseID, and including Country Code and Sea Region (used in Selection Criteria below). This query (or a table made from it) is used in the Aggregate queries.
| Description of specific aggregation query sequences | Nitrogen and Phosphate |
|---|---|
| Step 1 |
Crosstable query, with determinands "Nitrate", "Nitrite", "Total oxidised nitrogen" and "Orthophosphate" as columns, and row heading Sea Region, WaterbaseID, Year, Month, and SampleDepth. |
| Step 2 |
For each combination of WaterbaseID*Year*Month*Day, calculate [Total Oxidised Nitrogen]: Calculate best possible estimate of nitrate including nitrite:Oxidised Nitrogen is equal to Total Oxidised Nitrogen if Total Oxidised Nitrogen is measured, else calculate Oxidised Nitrogen equal to sum of Nitrate and Nitrite. Aggregate arithmetic mean of Oxidised Nitrogen and Orthophosphate over depths. |
| Step 3 |
For each combination of WaterbaseID *Year, calculate the arithmetic mean over the depth averages from Step 2. |
3. Classification of N and P concentration levels, for each station
For each (sub)regional sea, the observed concentrations are classified as Low, Moderate or High. Concentrations are classified as Low when they are lower than the 20-percentile value of concentrations within a (sub)region. Concentrations are classified as High when they are higher than the 80-percentile value of concentrations within a (sub)region. The classification boundaries therefore change between regional and/or sub-regional seas.
Trend analysis of Nitrogen and Phosphate concentrations
Consistent time series are used as the basis for assessment of changes over time. The trend analyses are based on time series from 1985 onwards. Selected stations must have at least data in the last four years of the current assessment (2007 or later), and 5 or more years in the overall assessment period (since 1985). For nitrogen nutrients nitrate+nitrite is used, but gaps may be populated with nitrate alone to complete the time series.. Trend detection for each time series was done with the Mann-Kendall Statistics using a two-sided test with a significance level of 5% (Sokal & Rohlf, 1995).
The Mann-Kendall method is a non-parametric test suggested by Mann (1945) and has been extensively used for environmental time series (Helsel and Hirsch, 2002; Hipel and McLeod, 2005). Mann-Kendall is a test for monotonic trend in a time series y(x), which in this analysis is nutrient concentration (y) as a function of year (x). The test is based on Kendall's rank correlation, which measures the strength of monotonic association between the vectors x and y. In the case of no ties in the x and y variables, Kendall's rank correlation coefficient, tau, may be expressed as tau=S/D where S = sum {i<j} (sign(x[j]-x[i])*sign(y[j]-y[i])) and D = n(n-1)/2. S is called the score and D, the denominator, is the maximum possible value of S. The p-value of tau is computed by an algorithm given by Best and Gipps (1974). The tests reported here are two-sided (testing for both increasing and decreasing trends). Data series with p-value < 0.05 are reported as significantly increasing or decreasing. The test analyzes only the direction and significance of the change, not the size of the change.
For oxidized nitrogen, the sum of nitrate and nitrite is used. However, if nitrite values are not available, gaps may be populated by assuming that oxidized nitrogen is equivalent to the prevalent nitrate fraction, in order to complete the time series.
The Mann-Kendall test for the detection of trends is a robust and accepted approach. However, due to the multiple trend analyses, approximately 5% of the tests conducted will turn out significant if in fact there is no trend. Also, the accuracy at the regional level is largely influenced by the number of stations for which data is available.
There are also a number of uncertainties related to temporal and spatial use of the data. Currently, the winter period is defined as January and February for all stations except for stations east of longitude 15 degrees (Bornholm) in the Baltic Sea. However, this definition may be too broad to reflect the climatic differences across the European sea regions. For example, for the Black Sea, it is suggested to also consider spring concentrations due to the nutrient enrichment of coastal waters as a result of increased riverine inputs (BSC, 2010).
Moreover, two types of geographical aggregation are performed in the current methodology, based on the Country Code and Sea Region. In both cases, differences in physical, chemical and biological characteristics between sampling stations are not taken into account. Measured nutrient concentrations should be related to natural background values that reflect spatial/geographical differences. Furthermore, data collected over the different years is obtained from different laboratories, possibly following different methodologies,,and it is being combined in the same trend analysis. This might influence the results as well.
Data for this assessment is still scarce considering the large spatial and temporal variations inherent to the European transitional, coastal and marine waters. Long stretches of European coastal waters are not covered in the analysis due to lack of data or sufficiently long and recent time series.
Trend analyses are only consistent for the North Sea and the Baltic Sea, for which data is updated yearly within the OSPAR and HELCOM conventions, as well as for some stations in Croatian coastal waters.
Due to variations in freshwater discharges and the hydro-geographic variability of the coastal zone and internal cycling processes, trends in nutrient concentrations as such cannot be directly related to measures taken in nearby river basins. However, overall trends reflect the effects of measures to reduce nutrient pollution.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/nutrients-in-transitional-coastal-and/nutrients-in-transitional-coastal-and-4 or scan the QR code.
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