Effects of Eutrophication

Since the 1800s, the Baltic Sea has changed from an oligotrophic clear-water sea into a eutrophic marine environment. Nitrogen and phosphorus are among the main growth limiting nutrients and as such do not pose any direct hazards to marine organisms. Eutrophication, however, is a condition in an aquatic ecosystem where high nutrient concentrations stimulate growth of algae which leads to imbalanced functioning of the system:

• intense algal growth: excess of filamentous algae and phytoplankton blooms;

• altered communities of fauna and flora;,

• production of excess organic matter;

• increase in oxygen consumption;

• oxygen depletion; and

• death of benthic organism, including fish.

Marine life can be suffocated by eutrophication

In the Baltic Sea, the excess biomass of primary producers accumulates on the sea-bed, and the decomposition of this organic material consumes oxygen from the water. This leads to oxygen depletion, especially in areas where water mixing is restricted, such as in deeper waters below the halocline, or in shallower waters affected by thermal stratification during the summer.