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You are here: Home / Data and maps / Indicators / Chlorophyll in transitional, coastal and marine waters / Chlorophyll in transitional, coastal and marine waters (CSI 023) - Assessment published Mar 2013

Chlorophyll in transitional, coastal and marine waters (CSI 023) - Assessment published Mar 2013

Created : May 21, 2012 Published : Mar 26, 2013 Last modified : Mar 27, 2013 11:19 AM

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Generic metadata

Topics:

Water Water (Primary topic)

Coasts and seas Coasts and seas

Tags:
SOER2010 | coastal | water | coastal water | thematic assessment | chlorophyll-a | marine and coastal | ecosystems
DPSIR: State
Typology: Descriptive indicator (Type A – What is happening to the environment and to humans?)
Indicator codes
  • CSI 023
Dynamic
Temporal coverage:
1985-2010
 
Contents
 
Switch to full indicator view

Indicator definition

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:

  • June to September for stations north of latitude 59 degrees in the Baltic Sea (Gulf of Bothnia and Gulf of Finland) 
  • May to September for all other stations 

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.

Units

The concentration of chlorophyll-a is expressed as microgram /l in the uppermost 10 m of the water column during summer.


Key policy question: Is eutrophication in European surface waters decreasing?

Key messages

  • In 2010, the highest summer chlorophyll-a concentrations were observed in coastal areas and estuaries where nutrient concentrations are also generally high (see CSI 021 Nutrients in transitional, coastal and marine waters). These include the Gulf of Riga, Gulf of Gdansk, Gulf of Finland and along the German coast in the Baltic Sea, coastal areas in Belgium and The Netherlands in the Greater North Sea and in few locations along the coast of Ireland and France in the Celtic Seas and Bay of Biscay, respectively. High chlorophyll concentrations were also observed along the Gulf of Lions and in Montenegro coastal waters in the Mediterranean Sea, and along Romanian coastal waters in the Black Sea. Low summer chlorophyll concentrations were mainly observed in the Kattegat and open sea stations in the Greater North Sea, and in open sea stations in southern Baltic Sea. 
  • Between 1985 to 2010, decreasing chlorophyll concentrations (showed in 8% of all the stations in the European seas reported to the EEA) were predominantly found along the southern coast of the Greater North Sea, along the Finnish coast in the Bothnian Bay in the Baltic Sea and in a few stations in the Western Mediterranean Sea and Adriatic Sea. In the Black Sea, it was not possible to make an overall assessment due to the lack of time series data. Increasing concentrations (observed in 5% of the reported stations) were generally observed in coastal locations in the Northern Baltic Sea but also in the open sea stations outside the north of the Celtic Seas. Most stations (87%) however showed no changes over time.

Chlorophyll-a concentrations in European seas in 2010

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.

Data source:
Downloads and more info

Observed change in chlorophyll-a concentrations in coastal and open waters of the Baltic, North East Atlantic and Mediterranean Sea, 1985-2010

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.

Data source:
Downloads and more info

Key assessment

Baltic Sea

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.

Greater North Sea

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). 

Celtic Sea, Bay of Biscay and the Iberian coast

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). 

Mediterranean Sea

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

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.



References

Data sources

Justification for indicator selection

The water quality in transitional, coastal and marine regions can be adversely affected by land-based and water-based anthropogenic activities, which outputs can reach directly or indirectly this environment. Most pollution comes from land-based activities, through inland waterways, such as the application of agricultural fertilizers and animal farming, or the discharge of poorly or untreated wastewater. Pollution can however also be airborne, from emissions, although this is more relevant for marine off-shore waters. These activities may result in elevated nutrient (mostly nitrogen and phosphorus) concentrations (see also CSI 021 Nutrients in transitional, coastal and marine waters) leading to eutrophication and causing a chain of undesirable effects. 

The primary effect of eutrophication is excessive growth of plankton algae which increases the concentration of chlorophyll-a. The negative effects of excessive phytoplankton growth are 1) changes in species composition and functioning of the pelagic food web, 2) increased sedimentation of organic material, and 3) increase in oxygen consumption that may lead to oxygen depletion and the consequent changes in community structure or death of the benthic fauna. The excessive settling of plankton algae may be enhanced by changes in species composition and functioning of the pelagic food web. Eutrophication can also promote harmful algal blooms that may cause discoloration of the water (and thus negative aesthetical impacts), foam formation, death of benthic fauna and fish, or shellfish poisoning of humans.

Measurements of chlorophyll-a, used as an estimate of phytoplankton biomass, are included in most eutrophication monitoring programmes, and chlorophyll-a represents the biological eutrophication indicator with the best geographical coverage at the European level (although coverage in Southern Europe is still not evenly distributed when compared to Northern Europe) . Measurements using satellite radiometers of water-leaving radiance in the visible range (ocean colour) are also nowadays used to determine the chlorophyll-a concentration. Chlorophyll-a can be estimated from ocean colour data at daily frequency and 250m horizontal resolutions.

Chlorophyll-a concentrations can also be used to assess the effects of measures taken to reduce eutrophication (i.e. through discharges of nutrients, namely nitrogen). However, due to variations in freshwater run-off, light climate, hydro-geographic variability of the coastal zone and internal cycling processes, trends in chlorophyll-a concentrations as such can not be directly related to measures, but must be evaluated in a broader context.

Scientific references:

Policy context and targets

Context description

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).

Targets

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.

Related policy documents

Methodology

Methodology for indicator calculation

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 (in line with the geographical regions specified in the MSFD) 
  2. Creating statistical estimates for each combination of station and year and deriving the average annual mean summer surface concentration of Chl-a
  3. Classifying Chl-a concentration levels for each station (i.e. according to low, moderate, and high boundaries)

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 SeaSubregional 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 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 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.

2. Annual concentration of Chl-a per station
The statistical aggregation for calculating annual concentrations for Chl-a is done in two- or three-stage query sequences, which include:
  • Selecting season (month) and depth 
  • If needed, building a cross-table with determinants in columns, and water samples in rows, and deriving composite determinants from that. 
  • Aggregating over depth for each combination of station and date. 
  • Aggregating over dates within each combination of station and year. 

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 sequencesChlorophyll

Step 1

Select query selecting data for determinand "Chlorophyll-a", and including Sea Region, WaterbaseID, date and SamplingDepth.

Include data for:

  • Depth less than or equal to 10 metres and
  • Month = 6,7,8,9 (Jun.-Sep.) for stations north of latitude 59 degrees in the Baltic Sea (Gulf of Bothnia and Gulf of Finland)
  • Month = 5,6,7,8,9 ( May-Sep.) for all other stations

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'

3. Classification of Chl-a 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 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.

Methodology for gap filling

n/a

Methodology references

Uncertainties

Methodology uncertainty

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 sets uncertainty

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.

Rationale uncertainty

Due to variations in freshwater run-off and hydro-geographic variability of the coastal zone and internal cycling processes, trends in chlorophyll-a concentrations as such can not be directly related to measures taken, but must be evaluated in a broader context.

More information about this indicator

See this indicator specification for more details.

Contacts and ownership

EEA Contact Info

Constança De Carvalho Belchior

Ownership

EEA Management Plan

2012 1.5.2 (note: EEA internal system)

Dates

First draft created:
May 21, 2012 11:09 AM
Publish date:
Mar 26, 2013 11:11 AM
Last modified:
Mar 27, 2013 11:19 AM
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