Finnish scientists came to the conclusion that the main reason for the rapid growth of anoxic zones in the Baltic Sea was household and agricultural waste falling into the sea water, according to Biogeosciences.

"Dead zones" are areas where there is practically no oxygen in the water and almost no living organisms. Such areas are in many seas: for example, recently scientists have told about the rapid growth of the "dead zone" in the Gulf of Oman. In the Baltic Sea, the most extensive zones of the oxygen minimum in the world are found: their total area reaches 70 thousand km2.

The authors of the new work analyzed two four-meter sedimentary core extracted from the bottom of the Archipelago Sea (between the Botnic and the Gulf of Finland). These samples allowed to restore about 1,5 thousand years of the history of formation of sediments. It turned out that the rate of oxygen loss in the last century has significantly accelerated. "Dead zones" left many living things, including mollusks and annelids. At the same time, such violations affect the inhabitants of neighboring areas of the sea.

According to scientists, the main reason for the growth of the oxygen minimum zones is domestic, industrial and agricultural wastewater.

They contain a large number of nutrients, for example nitrogen or phosphorus, which provoke the flowering of water. Dead algae sink to the bottom, where they are processed by bacteria. Microorganisms are actively consuming oxygen, so the pond gradually "suffocates". Scientists believe that this process can be slowed down if the amount of polluting emissions is reduced, but the restoration of some areas can take decades. Cyanobacteria can absorb nitrogen from the atmosphere, repeating the "vicious circle" of flowering water.

Source: "Around the world. Ukraine".