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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 Jan 2009

Chlorophyll in transitional, coastal and marine waters (CSI 023) - Assessment published Jan 2009

Indicator Assessment Created 13 Mar 2008 Published 29 Jan 2009 Last modified 07 Nov 2012, 06:34 PM
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Generic metadata


Water Water (Primary topic)

Coasts and seas Coasts and seas

soer2010 | thematic assessments | water | chlorophyll-a | marine and coastal | csi
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 023
Geographic coverage:
Belgium, Denmark, Estonia, Finland, Italy, Latvia, Lithuania, Malta, Netherlands, Norway, Poland, Sweden, United Kingdom

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

Key messages

The highest summer chlorophyll-a concentrations were observed in coastal areas and estuaries and are at many locations associated with nutrient inputs from major rivers. Of the 413 stations reported to the EEA in 2005 with more than 5 years of observations, decreasing trends in summer chlorophyll-a concentrations were found at 7% of stations, increasing trends were found at 8% of stations, and the majority of stations (85%) indicate no statistically significant change in concentration. The stations with descreasing trends are located either in the Baltic Sea or along the coast of Italy.

Map of summer chlorophyll-a concentrations observed in 2005

Note: 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

Data source:


Downloads and more info

Key assessment

NE Atlantic

It is not possible to make an assessment of summer chlorophyll-a in the NE Atlantic, because data for the year 2005 only includes observations from the Seine, Brest, Loire and Gironde River estuaries, France and observations from two Scottish stations (Figure 1). In the Seine, Loire and Gironde Estuaries, average summer chlorophyll-a concentrations exceed 6.6 g/l, and they were among the highest reported to the EEA in 2005 for all of the regional seas. All time series from the region are less than five years of duration and thus trend detection is not possible based on the information available.

North Sea

In the North Sea, the highest summer chlorophyll-a concentrations in 2005 were observed at the Danish North Sea stations, Belgian coastal stations and in the Scheldt Estuary. All three locations are impacted by water from large rivers (the Danish North Sea stations are impacted by water from the Elbe River, the Belgian stations by the River Scheldt, and possibly the River Rhine) and the high summer chlorophyll-a  concentrations in the sea are likely to reflect the high nutrient loads coming from the rivers feeding into those areas (Figure 1). Observations made at at stations updated to include 2005 show that concentrations have increased at 14 % of danish stations and 7% of Swedish stations in the North Sea (corresponding to one station in each country), and increased at 14% of the danish station, but the majority of stations (91%) show no statistically significant change (Figure 2, left).  Observations made prior to 2005 suggest a smiliar pattern (Figure 2, right).

Baltic Sea

In the Baltic Sea, summer chlorophyll-a concentrations were highest at Finnish coastal stations in 2005 and in the estuaries of the rivers Vistula and Oder (Figure 1) and the concentrations at these locations were among the highest observed in Europe. Concentrations increased at 21% of the Finnish stations and 25% of Lithuanian stations (Figure 2, left),  although concentrations also decreased at 7% of the Finnish stations.  Low concentrations are predominantly observed at Baltic open water stations (Figure 1) and decreasing concentrations are found at 9% of the Danish Baltic Sea stations (Figure 2, left). In recent years the Baltic Sea has suffered from frequent and extensive summertime blooms of cyanobacteria, which are partly responsible for increasing chlorophyll concentrations.

Mediterranean Sea

The Mediterranean Sea is oligotrophic and thus summer chlorophyll-a  concentrations are lower than in the other regional seas. In 2005, the highest summer chlorophyll-a  concentrations were observed along the North East coast of Italy, in proximity of the city of Naples (Figure 1). High concentrations were also observed at single stations in Malta,and in the Gulf of Orfani in Greece (Figure 1). Only Italy and Malta has submitted long enough time series to perform a trend analysis (Figure 2 left and right) which shows that summer chlorophyll-a  concentrations are increasing at 8% of the italian stations, decreasing at 5% of the stations, and no statistically significant trend can be detected at the remaining 87% of stations.

Black Sea

No chlorophyll-a observations made in Black Sea have been subteed to the EEA. 



Data sources

More information about this indicator

See this indicator specification for more details.

Contacts and ownership

EEA Contact Info

Constança De Carvalho Belchior


EEA Management Plan

2009 1.5.2 (note: EEA internal system)


Frequency of updates

Updates are scheduled once per year in July-September (Q3)
European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Phone: +45 3336 7100