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Indicator Assessment
Mean winter surface concentrations of phosphate in the Greater North Sea, the Celtic Seas and the Northeast Atlantic, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of phosphate in the Baltic Sea Area, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of nitrate+nitrite in the Black Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of nitrate+nitrite in the Mediterranean Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of nitrate+nitrite in the Greater North Sea, the Celtic Seas and the Northeast Atlantic, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Summary of trends in winter nitrate and phosphate concentration, and N/P ratio in the coastal waters of the North Atlantic (mostly Celtic Seas), the Baltic Sea, the Mediterranean and the North Sea, 1985-2003
Note: Trend analyses are based on time series 1985-2003 from each monitoring station having at least 3 years data in the period 1995-2003 and at least 5 years data in all
Waterbase (data from OSPAR, HELCOM, ICES and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of nitrate+nitrite in the Baltic Sea Area, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface nitrate/phosphate-ratio in the Black Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface nitrate/phosphate-ratio in the Mediterranean Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface nitrate/phosphate-ratio in the Greater North Sea, the Celtic Seas and the Northeast Atlantic, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface nitrate/phosphate-ratio in the Baltic Sea Area, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of phosphate in the Black Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
Mean winter surface concentrations of phosphate in the Mediterranean Sea, 2003
Note: Coastal stations are marked by circles and ICES open-water stations (>20 km from coast) by squares
Waterbase (data from OSPAR, HELCOM and EEA member countries compiled by ETC Water).
In the OSPAR (the North Sea, the English Channel and the Celtic Seas) and HELCOM (the Baltic Sea bounded by the parallel of the Skaw in the Skagerrak at 57o44.8'N) areas the available time-series show no clear trend in winter surface concentrations of nitrate. Both decreasing and increasing trends are observed at 3-4 % of the stations (Figure 1) which is certainly attributable to the temporal variability of nutrient loads resulting from varying run-offs.
In the Baltic Sea, winter surface nitrate concentrations are low, even in many coastal waters (the background concentration in the open Baltic Proper is around 65 microgram/l (EEA 2001)). The higher concentrations observed in the Belt Sea and the Kattegat are due mainly to the mixing of Baltic waters with the more nutrient-rich North Sea and Skagerrak waters. The enhanced concentrations resulting from local loading are particularly noticeable in the coastal waters of Lithuania, the Gulf of Riga, the Gulf of Finland, the Gulf of Gdansk, the Pommeranian Bay and Swedish estuaries (Figure 2).
In the OSPAR area the nitrate concentrations are high (>600 microgram/l) due to land-based loads into the coastal waters of Belgium, the Netherlands, Germany, Denmark, and in a few UK and Irish estuaries (Figure 13). Background concentrations in the open North Sea and Irish Sea are about 129 microgram/l and 149 microgram/l, respectively (EEA 2001). In the Dutch coastal waters, an overall decrease of 10-20% in winter nitrate concentrations has been observed, when normalising the concentration to salinity and using a smoothing trend detection method. Denmark reported significant decreasing trends in the annual mean concentrations of nitrate+nitrite+ammonium, both in coastal waters and in the open Kattegat and Belt Sea.
In the Mediterranean Sea, nitrate concentrations have increased at 24 % and decreased at 5 % of the Italian coastal stations (Figure 1). The background concentration is low, i.e. only 7 microgram/l. Relatively low concentrations are observed in the Greek coastal waters, around Sardinia and the Calabrian Peninsula. Slightly higher concentrations are observed along the north-west and south-east Italian coasts. High concentrations are observed in most of the northern and western Adriatic Sea, as well as close to rivers and cities along the Italian west coast.
In the Black Sea, the background concentration of nitrate is very low, i.e. 1.4 microgram/l (Figure 11). A slight decrease in nitrate concentration has been reported in the Romanian coastal waters, with a steady decline in the Turkish waters at the entrance to the Bosphorus (Black Sea Commission 2002). An increased level of both nitrate and phosphate in Ukrainian waters during recent years is connected to high river run-offs (Black Sea Commission 2002).
In the Baltic and North Seas, phosphate concentrations have decreased at 25 % and 33 % of the coastal stations, respectively (Figure 1). In the Greater North Sea, the decline in phosphate concentrations is especially evident in the Dutch and Belgian coastal waters, which is probably due to reduced phosphate loads from the river Rhine. Decreases in phosphate concentrations have also been observed at some stations in the German, Norwegian and Swedish coastal waters, and in the open North Sea (more than 20 km from the coast). In the Baltic Sea area, decreases in phosphate concentrations were observed in the coastal waters of most countries, except Poland, as well as in the open waters.
In the Baltic Sea area (Figure 10), the winter surface phosphate concentration is very low in the Bothnian Bay compared with the background concentrations in the open Baltic Proper, and is potentially limiting primary production in the area. The concentration is slightly higher in the Gulf of Riga, the Gulf of Gdansk, in some Lithuanian, German and Danish coastal waters and in estuaries. Remedial measures have been taken in the catchment areas and a reduction in the use of fertilisers has occurred. However, recent research indicates that phosphate concentrations, for example in the open Baltic waters including the Kattegat, are strongly influenced by processes and transport within the water body due to variable oxygen regimes in the bottom water layer (Rasmussen et al. 2003). The phosphate concentration is exceptionally high in the Gulf of Finland due to hypoxia and the up-welling of phosphate-rich bottom water in the late 1990s (HELCOM 2001).
In the North Sea, the English Channel and the Celtic Seas, phosphate concentrations in the coastal waters of Belgium, the Netherlands, Germany and Denmark are elevated compared to those of the open North Sea. The concentrations in the estuaries are generally high due to local loads (Figure 9).
In the Mediterranean Sea, phosphate concentrations have increased at 26 % and decreased at 8 % of the Italian coastal stations (Figure 1). Concentrations higher than the background value (i.e. about 1 microgram/l) are observed in most coastal waters, and much higher concentrations are observed in hot spots along the east and west coasts of Italy (Figure 8).
In the open Black Sea, the background phosphate concentration is relatively high (about 9 microgram/l) compared with the Mediterranean Sea and the background nitrogen value. This is probably due to the permanently anoxic conditions in the bottom waters of most of the Black Sea, which prevent the phosphate from being bound in the sediments. The phosphate concentration along the Turkish coast is lower than in the open sea, while it is higher in the Romanian coastal waters influenced by the Danube River (Figure 7). In the Black Sea, a slow decline in the concentrations of phosphate has been reported in the Turkish waters at the entrance to the Bosphorus (Black Sea Commission 2002).
In the Baltic Sea, the N/P ratio, based on winter surface nitrate and phosphate concentrations, is increasing in all areas (Figure 1) except the Polish coastal waters. The N/P ratio is high (>32) in the Bothnian Bay, where it is likely that phosphorus limits the primary production of phytoplankton. However, the N/P ratio is low (<8) to relatively low (<16) in most of the open and coastal Baltic Sea area, indicating that nitrogen can be a potential growth-limiting factor (Figure 6).
In the Greater North Sea and Celtic Seas, high N/P ratios (>16) are observed in the Belgian, Dutch, German and Danish coastal waters and estuaries (Figure 5), indicating potential phosphorus limitation, at least early in the growing season. In more open waters, the N/P ratio is generally below 16, indicating potential nitrogen limitation.
In the Mediterranean Sea, high N/P ratios (>32) are found along the northern Adriatic coast and at hot spots along the Italian coasts and the north coast of Sardinia (Figure 4), indicating potential phosphorus limitation, at least during some periods of the growing season.
In the Black Sea, the N/P ratio is generally low, especially in the open sea and along the Turkish coast, indicating potential nitrogen limitation. High N/P ratios (>32) are found only at a few Romanian coastal stations (Figure 3), indicating potential phosphorus limitation.
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 or scan the QR code.
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