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Signs of recovery in the Baltic Sea

Despite dead zones and algal blooms – the Baltic Sea is getting better. The improvements are according to a study carried out by Danish, Swedish and Finnish scientists a direct result of reduced inputs of nutrients.
Swimming in the Baltic Sea in Copenhagen.
The Baltic Sea has been cleaned up enough to be able to swim in the harbour of Copenhagen. Photo: Creative Commons

Thirty-five years ago swimming was prohibited in some areas around the Baltic Sea. Today there is an outdoor swimming pool in the harbour of the city of Copenhagen, Denmark because of reductions in pollution loadings. The open waters of the Baltic Sea are also cleaner today as shown in a new unique study by Danish, Swedish and Finnish scientists.

– Our studies have shown improvements in water quality in most parts of the Baltic Sea, says Professor Daniel Conley in the Department of Geology, Lund University.

The article ”Long-term temporal and spatial trends in the eutrophication status of the Baltic Sea”, which has been published recently in the scientific journal Biological Reviews, reveals a unique overview of how the effects of nutrient enrichment has developed in different parts of the Baltic Sea over a 112 year period, from 1901 to 2012.

– Our study documents the very first signs of recovery in the Baltic Sea. Our work clearly demonstrates that long-term efforts to reduce inputs of nutrients – especially nitrogen and phosphorus, now are having large-scale effects.

Significant improvements are seen in the Kattegat. The same positive signals are found on other areas, even in an area like the southern Baltic Proper.

Nutrient enrichment of the Baltic Sea – also known as eutrophication – is often debated in more negative terms, not at least in the media. The coverage of areas depleted of oxygen, so-called dead zones is record high and algal blooms are a significant problem in many areas.

Is it really true that the negative trend of eutrophication in the Baltic Sea has been reversed?

– Yes! The available data show clear improvements, answers Daniel Conley.

– Indicators of environmental conditions show significant improvements in the surface waters, while bottom waters of the sea have worsened. However, overall we see that the improvements outweigh the setbacks. 

The study also evaluates monitoring activities and the access to data used for assessing the eutrophication status.

During 1970s and 1980s, all Baltic Sea countries started harmonized and coordinated monitoring activities. But since then, especially during the recent 10 years, data availability has declined.

This decline, especially if it is accelerated, could potentially have profound implications in regard to our capabilities to document temporal trends in the environmental status of the Baltic Sea and to our ability to understand changes in the ecology of the Baltic Sea.

– Billions are being spent on reducing inputs of nutrient to the Baltic Sea in order to reduce the effects of eutrophication. It could seem illogical, that adequate resources are not allocated to document the positive effects of huge investments.


Denmark: Jesper Andersen, NIVA Danmark Water Reasearch + 45 2031 3221

Finland: Alf Norkko, Helsinki University + 338 2941 28104

Sweden: Bo Gustavsson, Stockholm University + 46 8 674 7593

International: Daniel J. Conley, Lund University + 46 7 749 4341

Facts: This is how we did it

Baltic Sea

The scientists have collated huge data sets consisting of historical environmental data from national marine monitoring activities. An important source was the BED database, hosted by the Baltic Nest Institute at Stockholm University’s Baltic Sea Centre. Based on internationally agreed environmental assessment criteria in combination with a multi-metric indicator-based eutrophication assessment tool (HEAT 3.0), long-term trends in nutrient enrichment and eutrophication has been mapped in the different parts of the Baltic Sea over a 122 year long period.

The article in Biological Reviews can be downloaded via this link:

Facts: Nutrient enrichment and eutrophication in a 100 year perspective

For hundred year ago, the open parts of the Baltic Sea were classified as "unaffected by eutrophication". Eutrophication became a significant and large-scale problem during the 1950ies as inputs from land increased. A culmination in regard to eutrophication was reached in the beginning of the 1980’ies. Since then, external nutrient loads have declined gradually due to improved waste water treatment and to reduction of emission, discharges and losses from the agricultural sector.

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