Eutrophication – causalities,monitoring and time lag in recovery: experiences from the Baltic Sea region

Eutrophication – causalities, monitoring and time lag in recovery: experiences from the Baltic Sea region

The negative effects of excess of nutrients in marine systems are well described from many areas around the world. The Baltic Sea region is particularly effected due to a high population density and intense agricultural activities in the catchment leading to high nutrient inputs. This, combined with a long residence time, means that the Baltic Sea and many of its coastal areas are severely affected by eutrophication. Therefore, all countries around the Baltic Sea has agreed to reduce nutrient inputs. This is also the case for Denmark, where eutrophication is widespread and severe. The reduction in nutrient inputs have been around 50 percent for nitrogen and 90 percent for phosphorous in Denmark and somewhat similar for the Baltic Sea. Clear improvements in the marine environment are observed thanks to a well-established monitoring program, but it is also evident that there is a considerably time lag from nutrient reductions take place to the full effect is realized found in the marine environment. For smaller estuaries, the time lag is in the order of two-three decades, where it is estimated to about 400 years for the Baltic Sea.

In this lecture, the mechanisms for eutrophication are discussed based on 30 years’ experience in the Baltic Sea region and a hypothesis is presented for the mechanisms for time lag and tipping points in marine eutrophication during a phase with reduced nutrient inputs.

Dr. Stiig Markager is a professor in biogeochemistry and marine ecology at Aarhus University Denmark. He has been working about marine eutrophication for 24 years and is a member of the expert groups in HELCOM (Baltic Sea) and OSPAR (the North Atlantic) for eutrophication.