The Baltic Sea water is getting warmer. “Phytoplankton is increasing, oxygen is decreasing”

Water temperature in the Baltic Sea, from Swinoujscie after Heliumhas remained at 20 degrees Celsius in recent weeks. Scientists also confirm the clear warming of the “Polish” sea in recent decades. – The water in the Baltic Sea has been warming up significantly over the past decades. This is indicated by temperature measurements and clear changes that we notice in its ecosystem. In 1990, the average temperature of the Baltic Sea was 7.7 degrees, while in 2023 it will be 9.5 degrees – said Dr. Artur Skowronek from the Institute of Marine and Environmental Sciences of the University of Szczecin. This data comes from the German Institute for Baltic Research in Warnemünde – Leibniz-Institut für Ostseeforschung. – Phytoplankton is also increasing, there are algae and cyanobacteria blooms, species of aquatic plants that prefer higher temperatures appear, for example brown algae, and algae that prefer cooler waters, such as the once common fucus, are becoming increasingly rare – added the scientist.

Should the Baltic Sea temperature, which remains at around 20 degrees Celsius in the summer, worry us? As Skowronek noted, the water in different parts of the sea and at different depths has always been, is and will be different. There is no universal “just right” temperature.

– The decisive phenomenon influencing the water temperature in summer in many locations on the Baltic coast is not the air temperature, but the strength and, above all, the direction of the wind – said the doctor. – Regular, several-day winds blowing from the land push warm surface waters to the open sea, and cold water from deeper parts of the sea flows in their place. This is the phenomenon of the so-called upwelling – he explained. According to the researcher, in 20 years the Baltic Sea is unlikely to become a very warm sea, where conditions will be similar to those we know from southern Europe. – However, it may change even more, and rather for the worse. Unfortunately, even more intense blooms should be expected Cyanobacteria and changes in water parameters, especially a decrease in its oxygenation – said Skowronek. An increase in water temperature brings many consequences. – A change in each water parameter – temperature, of course – brings consequences. There are several basic principles that are based on physicochemical phenomena. One of the most important is the dependence of the oxygen content dissolved in water on temperature. The general rule is that the warmer the water, the lower the content of dissolved oxygen, which is necessary for aquatic organisms to live – explained the scientist. He added that water temperature and sunlight therefore have a direct impact on the development of phytoplankton. – With an appropriate supply of nutrients – nitrogen compounds, but above all phosphorus – there is a lush development of algae, phytoplankton and the famous cyanobacteria. Their mass occurrence causes a sudden increase in biomass, which dies after a short time and is decomposed by microorganisms that need oxygen for their metabolism – he added. So will there be less and less oxygen in water? According to the doctor, this is where a serious problem begins. – Oxygen, which is less dissolved in warm water anyway, is used up in the bottom zone by microorganisms and is not available to other organisms, such as vertebrates, which may not survive such a stifling experience – he said. The researcher noticed that there is another aspect related to phytoplankton blooms: abrupt changes in water pH. Phytoplankton need carbon dioxide CO2 for photosynthesis and take it from the water. – A significant loss of CO2 (with an acidic pH) in water causes a change in the water pH towards alkaline, the water can become downright toxic to sensitive organisms and cause, for example, gill burns or the death of fry. Another important relationship is the effect of temperature on the intensity of biological decomposition of organic remains, mainly accumulated in bottom sediments – explained Skowronek.

As the researcher said, most lakes are filled with sediment with a high content of organic remains, plants and animals, which can reach a thickness of several meters. – These sediments are home to abundant life. Various organisms live and feed in them, such as mussels or insect larvae, but also microorganisms. These include bacteria that need oxygen to live and those whose metabolism is based on anaerobic respiration. Both produce gases, the former carbon dioxide, anaerobes methane or hydrogen sulphide. The activity of these organisms is favored by higher temperatures. This means that as the water temperature in the reservoirs increases, the production of these gases will increase, which means further consequences in the ecosystem – he said.

What other long-term consequences of systematic warming will there be? – There will be many of them and we certainly do not know about all of them. One of the most serious problems is the rise in sea level. We will lose coastal areas – sea erosion cannot be prevented, it can only be limited and slowed down – he said. Secondly – the intensity of extreme weather phenomena, such as storm surges, will increase. Thirdly – in many areas the level of groundwater will also rise, causing seepage and the formation of wetlands, and even changing the load-bearing parameters of the land. Another problem is the increasingly frequent droughts, including hydrological ones. This has serious consequences for agriculture, the supply of drinking water, but also for technological water, e.g. cooling water for power plants, inland navigation or even recreation and related economic activities. The risk of forest fires is also increasing.