Despite dead zones and algal blooms – the Baltic Sea is recovering

The improvements are according to a study carried out by Danish, Swedish and Finnish scientists a direct result of reduced inputs of nutrients.

The improvements are according to a study carried out by Danish, Swedish and Finnish scientists a direct result of reduced inputs of nutrients.

Thirty-five years ago swimming was prohibited in many areas around the Baltic Sea. Today there is an outdoor so-called ‘harbour bath’ in the inner 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.

– We can document improvements in most open parts of the Baltic Sea, says Jesper Andersen, chief scientist (PhD) at NIVA Denmark Water Research.

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 sign of recovery in the Baltic Sea. It is a relief to see 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! Based on available data, Jesper Andersen answers.

– Indicators representing environmental conditions in upper water masses have improved significantly, while the situation nearer the bottom of the sea has worsened. But in total, we see that improvements outweigh setbacks.

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

During 1970ies and 1980ies, 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.

Facts: This is how we did it

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.

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.


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

Last updated 27.10.2015