Eutrophication is the biggest problem for the Baltic Sea

Eutrophication is the biggest problem for the Baltic Sea, and the Gulf of Finland is its most badly affected basin. Though eutrophying nutrient discharges have decreased lately, there has been an increase in the visible symptoms of eutrophication, such as blue-green algae, water opacity, beach mucilage and the number of anoxic seafloor areas. According to current estimates, climate change will further precipitate the eutrophication of the Baltic Sea.

Nutrients promote algae growth

Eutrophication is caused by nitrogen and phosphorus emissions, which nourish the growth of algae in the water. With respect to the occurrence of blue-green algae, phosphorus, in particular, plays a key part. Nitrogen and phosphorus drift into the sea in wastewater from cities and along with rainwater from fields, for example. In addition, part of the nitrogen emissions caused by traffic ends up in the Baltic Sea as fallout from the air. With regard to Finland's nutrient load, the proportion of agriculture is large: its share of the nitrogen load is approximately one third, and almost half of the phosphorus load.

Anoxic seafloors

Ample growth of small algae, i.e. phytoplankton, in the surface waters cause the oxygen to run out in the water areas near the bottom. Dead algae sink to the bottom, and their decomposition consumes oxygen from the seafloor. Under anoxic circumstances, the process of decomposition changes and begins to produce poisonous hydrogen sulphide, which kills the animal populations at the bottom of the area. In addition, phosphorus is released from the seafloor. This is called internal loading of the sea. If the water mixes very powerfully, the phosphorus released from the seafloor reaches the water surface layers and promotes the extensive growth of blue-green algae.

Changing ecosystems

In addition to microscopic algae, the large amount of nutrients in the water also precipitates the growth of annual filament algae on the stony beaches and cliffs. The more frequent filament algae suffocate the perennial algae of the Baltic Sea, such as bladder wrack, which has a significant role in the ecosystem of the Baltic Sea. Bladder wrack forms rich growths in shore waters, which act as an important spawning area and a ‘nursery’ for many fish species, including financially important ones.

Eutrophication has far-reaching consequences

Eutrophication is changing life in the Baltic Sea. The effects also reach financially important fish populations, not to speak of the detrimental effect the eutrophication symptoms have on tourism, for example. In order to curtail emissions, all countries around the Baltic Sea should start cooperating and take concrete action.