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Baltic Sea suffers from eutrophication

Photo: HELCOM/Nikolay Vlasov
Photo: HELCOM/Nikolay Vlasov
Eutrophication is the major environmental problem of the Baltic Sea. It destroys the quality of the marine environment and reduces attractiveness, competitiveness and thus welfare of the whole region. Eutrophication is caused by excess load of nutrients - nitrogen and phosphorus - to the sea mainly from land-based sources. The availability of nutrients is one of the primary factors limiting the growth of aquatic plants and algae. Nutrient flow from land to the watercourses as such is a natural process, but human activities, e.g. habitation, industry, agriculture and forestry have multiplied the amount of nutrients discharged to lakes, rivers and seas. Baltic Sea suffers also from internal nutrient loading. Eutrophication increases oxygen consumption at the sea bottom due to intensified bacterial decomposition. In low-oxygen conditions, the phosphorus that has been bound in bottom sediments is released back into water.

Eutrophication alters the Baltic Sea fauna and flora. High amount of nutrients in the water promotes intense growth of microscopic planktonic algae and thereby decreases the transparency of water. The decomposition of dead algal mass causes oxygen depletion on bottom areas and creates dead zones where marine life cannot survive. Filamentous algae thrive in the turbid water and make seashores, beaches and fishnets slimy. Many economically important fish species’ spawning areas are deteriorated due to eutrophication. In many ways, phosphorus is the key nutrient and e.g. the massive occurrences of harmful blue-green algae are caused mainly by the overload of phosphorus.