In open sea areas, good environmental status (GES) for chlorophyll-a has been achieved in the Kattegat and Gulf of Riga. In the remaining 15 sub-basins, GES has not been achieved.
In many sub-basins the summer-time chorophyll-a has increased until the 1990's (Arkona Sea, Kattegat) or early 2000's (Bothnian Bay, Northern Baltic Proper, Gulf of Riga, and Western Gotland Basin), but turned to decrease thereafter. Only in the Gulf of Finland, Bothnian Sea and Eastern Gotland Basin, increase has continued.
The confidence of the presented chlorophyll-a status estimate is low in the Gulf of Riga, Gulf of Finland, Åland Sea, Bothnian Sea, Quark and Bothnian Bay, due to lack of monitoring data.
Average chlorophyll-a concentration in the surface (0 – 10 m) during summer (June – September). (Open dynamic map viewer in new tab)
Phytoplankton increases along with increased eutorphication, as a result of increased nutrient concentrations. Chlorophyll-a concentration is used as a proxy of phytoplankton biomass. This core indicator focuses on one important aspect of the complex phenomenon, but does not alone assess the eutrophication status.
BSAP segment and objective
A Baltic Sea unaffected by eutrophication
MSFD descriptor and criteria
5.2. Direct effects of nutrient enrichment
Other relevant legislation
Water Framework Directive
Pyhälä M, Fleming-Lehtinen V, Laamanen M, Łysiak-Pastuszak E, Carstens M, Leppänen J-M, Leujak W, Nausch G, 2014. Chlorophyll-a status - HELCOM Core Indicator Report. Online. [Date Viewed], http://www.helcom.fi/baltic-sea-trends/indicators/chlorophyll-a