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Indicator Assessment
Chlorophyll-a concentrations in European seas in 2010
Note: The map shows Chlorophyll-a concentrations in European coastal and open seas in 2010. The class boundaries “high”, “moderate” and “low” concentration are determined by the 80/20 percentiles of the data set in each sea (sub)region. 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.
Trend in summer chlorophyll-a concentrations in coastal and open waters of the Baltic, Celtic and Mediterranean Seas and NE Atlantic, 1985-2010
Note: This figure shows stationwise trends in chlorophyll-a 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 statistically significant change, within the years 1985–2010). Numbers in parentheses indicates 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 change in chlorophyll-a concentrations in coastal and open waters of the Baltic, North East Atlantic and Mediterranean Sea, 1985-2010
Note: The map shows stations with a statistically significant decrease (green), increase (red) or no trend (yellow) 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. Note that the open sea stations around Faroe Islands are included under Celtic Seas.
In 2010, the highest measured summer chlorophyll-a concentrations (>12.2 µg/l) were found in German waters along the Mecklenburg coast and the Gulf of Gdansk, and in a few locations in the Gulf of Riga and Finalnd. Low concentrations were predominantly observed in the open waters of the southern Baltic Sea (Figure 1).
Most of the stations (87%) did not show a significant change in chlorophyll concentration in the period 1985-2010. Overall, statistically significant decreasing trends were evident in 7% of the Baltic Sea stations (Figure 2). Chlorophyll concentrations decreased in Finnish coastal areas of the Bothnian Bay and at discrete stations in the Baltic Proper. In contrast, increases were observed in particular in the Gulf of Finland, and at some coastal stations in the Gulf of Bothnia and along the southern Baltic coast. Statistically significant increasing trends were evident in 7% of the Baltic Sea stations (Figure 3). In fact, HELCOM (2009, 2010) recognizes that eutrophication is a problem in large parts of the Baltic marine ecosystem.
In 2010, the highest summer chlorophyll-a concentrations (> 8.9 µg/l) were observed along the coast of Belgium and The Netherlands (Figure 1). These areas are also characterized by elevated concentrations of nutrients (see CSI 021) and frequent blooms of Phaeocystis globosa (OSPAR, 2008). According to OSPAR (2010), further actions are needed to improve problem areas like the continental coast of the Greater North Sea. Low chlorophyll concentrations were predominantly observed in the open waters of The Netherlands and in the Kattegat (Figure 1).
The majority of the stations (88%) did not show a statistically significant change in chlorophyll concentration between 1985 and 2010. In 10% of the stations, found in transitional and coastal waters along the continental coast, a statistically significant decreasing trend was observed whereas 2% of the stations (located in the open sea) showed an increasing trend (Figure 2, 3).
Generally, chlorophyll concentrations in the Celtic Seas, Bay of Biscay and the Iberian coast were generally low (< 2 µg/l) in 2010, with the exception of a few transitional water stations along the Irish and French coast (Figure 1). OSPAR (2008) has defined small coastal embayments and estuaries within the Celtic Seas and the Bay of Biscay and Iberian Coast as problem areas with respect to eutrophication.
A significantly increasing trend was observed in 15% of the stations, predominantly in open sea stations, whereas no trend was observed in the majority of the other stations (Figure 2, 3).
In 2010, only data from France,Croatia and Montenegro were available (Figure 1). The highest summer chlorophyll-a concentrations (> 5 µg/l) were observed in transitional and coastal waters of France and Montenegro. No offshore data of the Mediterranean chlorophyll concentrations have been reported to the EEA for the year 2010. The open waters of the Mediterranean Sea are, however, poor in nutrients and thus summer chlorophyll-a concentrations are also low.
Only France and Croatia have submitted long enough time series data to estimate trends. In 12% of these Mediterranean stations, significant decreases were observed, while no increases were observed in any of the stations. Significantly decreasing trends were observed in 16% of the French stations, mainly in the Gulf of Lions and in one (5 %) of the Croatian stations (Figure 2, 3).
Recent regional assessments show that nutrient over-enrichment, possibly leading to eutrophication and hypoxia, occur mainly in developed coastal areas and 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) (UNEP/MAP, 2012).The most eutrophic waters in Mediterranean are along the northern coastline, but eutrophication problem has been increasing gradually over the last decades also in the southern shore of the sea (UNEP/MAP 2007). Harmful algal blooms have been observed commonly in the northern coastal areas. These blooms have also consisted of dinoflagellates (e.g. Dinophysis and Alexandrium) potentially causing different types of shellfish poisoning (Koukaras and Nikolaidis 2004, Bravo et al. 2008).
Black Sea data for the year 2010 consisted of a number of coastal measurements along the Romanian coast near the Danube estuary, which showed high to moderate levels of concentration. The time series was too short to perform a trend analysis.
The indicator shows 1) annual mean summer surface concentrations (microgram/l), 2) classification of concentration levels (i.e. low, moderate, high) and 3) trends in mean summer surface concentrations of chlorophyll-a (microgram/l) in the regional seas of Europe.
Summer period is:
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.
The concentration of chlorophyll-a is expressed as microgram /l in the uppermost 10 m of the water column during summer.
There are a number of EU Directives aimed at reducing the loads and impacts of nutrients. These include: the Nitrates Directive (91/676/EEC) aimed at reducing nitrate pollution from agricultural land; the Urban Waste Water Treatment Directive (91/271/EEC) aimed at reducing pollution from sewage treatment works and certain industries; the Integrated Pollution Prevention and Control Directive (96/61/EEC) aimed at controlling and preventing pollution of water from industry; and 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 acheivement or maintenance of good environmental status in European sea basins by the year 2020 at the latest, through the adoption of plans of action based on 11 qualitative descriptors, one of which is Eutrophication.
Measures also arise from a number of other 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) on the Protection of the Marine Environment of the Baltic Sea Area; OSPAR Convention 1998 for the Protection of the Marine Environment of the North East Atlantic; and the Black Sea Environmental Programme (BSEP).
Natural and background concentrations of chlorophyll vary between regional seas, between sub-areas within the same regional sea, and between different water bodies types within a sub-area depending on physical and biological factors, such as natural nutrient loads, water residence time and annual biological cycling.
The most pertinent target with regard to chlorophyll concentrations arises from the Water Framework Directive. Target chlorophyll concentrations/ranges that support the biological quality elements at a good status (high-good boundary and good-moderate boundary) have been defined in the Commission Decision (2008/915/EC) based on the results of the intercalibration exercise carried out by the geographical intercalibration groups in Baltic Sea, North East Atlantic and Mediterranean. These target chlorophyll concentrations/ranges are determined locally for different water types and water categories, including coastal and transitional water bodies.
Chlorophyll concentration in the water column is considered as an indicator of the direct effect of nutrient enrichment in marine waters under Marine Strategy Framework Directive’s Good Environmental Status Descriptor 5: Human-Induced Eutrophication. The assessment of eutrophication in marine waters needs to take into account the assessment for coastal and transitional waters under the Water Framework Directive and related guidance, in a way which ensures comparability, taking also into consideration the information and knowledge gathered and approaches developed in the framework of regional sea conventions. Chlorophyll targets or thresholds for achieving good environmental status in marine water have not yet been determined.
Methodology for indicator calculation (including description of data used)
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.
Annual mean summer surface concentrations of Chl-a, 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.
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 were 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.
The basic data consists of two tables:
| Measurements values table |
|---|
| WaterbaseID (Country and Station) |
| Date (Year, Month and Day) |
| SampleDepth |
| SampleID |
| Determinant with the Determinant code "Chlorophyll" |
| Stations table |
|---|
| Unique identifier: data provider, Country and StationID |
| 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 | Chlorophyll |
|---|---|
|
Step 1 |
Select query selecting data for determinand "Chlorophyll-a", and including Sea Region, WaterbaseID, date and SamplingDepth. Include data for:
For each combination of WaterbaseID*Station*Date, calculate arithmetic mean of chlorophyll-a over depths. |
|
Step 2 |
For each combination of WaterbaseID*Year, calculate the arithmetic mean over the depth averages from Step 1. Export result to Aggregate database as table 't_Base_Metadata_Chl_a' |
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 Chl-a 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). 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 chlorophyll 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.
n/a
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 two growing seasons are distinguished, one for the northern part of the Baltic Sea (June- September) and one for the southern part of the Baltic Sea, the North Sea, NE Atlantic waters, Mediterranean and Black Sea (May-September). It is questionable whether using one growing season for all waters that range geographically from the Mediterranean and the Black Sea to the North Sea and Baltic Sea, is appropriate. Moreover, currently only surface concentrations are considered. However, in the Black Sea, not only do the chlorophyll concentrations show peaks in late winter, late spring and autumn, these peaks do not only occur at the surface but also in subsurface layer (BS SoE, 2008).
Data for this assessment are still scarce considering the large spatial and temporal variations inherent in European transitional, coastal and marine waters. Long stretches of European coastal waters are not covered by the analysis due to lack of data. Trend analyses are only consistent for the eastern North Sea, the Baltic Sea area and French and Croatian coastal waters in the Mediterranean.
For the assessment of chlorophyll-a concentrations, different analytical methods are generally used. Although these different analytical methods generally give comparable results with reasonable to good correlations between methods, simple fluorometric and photometric methods are less accurate and therefore may be a source of uncertainty.
Low sampling frequencies increase the risk of not detecting phytoplankton blooms, and differences in sampling frequency between stations are an additional source of uncertainty.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/chlorophyll-in-transitional-coastal-and/chlorophyll-in-transitional-coastal-and-3 or scan the QR code.
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