Sub-regional assessment of eutrophication status in the Baltic Sea

Figure: Overview of eutrophication classifications per sub-basin based on the application of the HELCOM Eutrophication Assessment Tool (HEAT).

All sub-basins except for the Quark have areas classified as poor or bad. All areas assessed in the Gulf of Riga were assessed to have a bad eutrophication status. All basins of the Baltic Sea including the open parts of the Bothnia Sea were classified as affected by eutrophication. The reason for classifying the open parts of the Bothnian Sea as affected is related to a well-documented increase in chlorophyll-a concentrations (see HELCOM 2009 for details). For most of the coastal water in the Baltic Sea, the general picture is that nutrient concentrations and chlorophyll-a concentrations are elevated, not only compared to so-called reference conditions but also compared to target values. For most open basins, the benthic invertebrates are outside the range of what is being considered as being a good status. Only four out of 110 coastal waters were classified as having good or high status. All of these four areas are located in the Gulf of Bothnia. It is noteworthy that all coastal areas outside the Gulf of Bothnia are classified as affected by eutrophication. The explanations for having impaired conditions include elevated levels of nutrients and chlorophyll-a, loss of submerged aquatic vegetation as well as periods of oxygen depletion affecting in particular benthic invertebrates.

References

HELCOM 2009. Eutrophication in the Baltic Sea – An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region. Helsinki Commission. Baltic Sea Environment Proceeding No. 115B.

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Last updated: 19 February 2010