The Dying Baltic Sea: When Will Lithuania Face the Consequences?

The so-called dead zone formed in the Baltic Sea is one of the largest in the world. In the latest episode of the Vilnius University (VU) podcast "Mokslas be pamokslų" ("Science Without Sermons"), Kęstutis Jokšas, Associate Professor at the Faculty of Chemistry and Geosciences, talks about the reasons behind this issue, explains what dead zones are in general, and argues what consequences marine pollution will have on Lithuania. According to the scientist, the world’s largest dead zone lies in the Arabian Sea, the second by size can be found in the Gulf of Mexico, while the third lurks in the Baltic Sea.

What is a dead zone?

Assoc. Prof. Dr Jokšas explains that a dead zone refers to an area with a reduced level of oxygen in the water. Such places are also known as hypoxic areas, oxygen minimum zones, or biological deserts. Oxygen is vital for most living organisms; thus, in oxygen-deprived environments, few organisms can survive: aquatic plants tend to disappear, and animals either leave their natural habitats or are doomed to die.

"Researchers have found that dead zones are expanding, and oxygen levels in the global ocean have declined by 2% over the last 50 years. Marine species respond to ocean deoxygenation and can abandon such areas. For instance, fish are capable of swimming long distances to reach different locations. Yet, some life forms are less mobile than others – algae and other organisms that live on the seafloor, as well as molluscs and shrimps, find it difficult to leave such zones. This means they either develop various diseases, die, or stop reproducing, expanding their population and ecosystem, and so on," says the VU researcher.

According to him, dead zones are quite widespread in the world’s oceans. The first one was reported in 1950. As explained by Assoc. Prof. Dr Jokšas, that year, scientists all around the globe recorded about 50 dead zones in total. Recently, the number of such areas in the global ocean has reached around 530 and is further increasing each year.

"They can vary in size from a few tens of square kilometres to several hundred, even up to 1,000 km2. At the moment, these low-oxygen areas are estimated to cover approximately 4.5 million km2. Originally observed next to the coast of America, in the Gulf of Mexico, they are now found in huge numbers near the Kuril Islands in Japan, in the Kamchatka region, and in the South Atlantic Ocean on the west coast of South Africa," states the scientist.

Why do dead zones occur?

According to Assoc. Prof. Dr Jokšas, dead zones can be triggered either by natural or anthropogenic factors. Often, both causes are at work. Some such zones may only occur seasonally or at specific times of the day, week, or month.

The scientist points out that there are many such areas in the Baltic Sea: "The most common cause behind this issue is eutrophication – excessive plant and algal growth determined by the overabundance of chemical nutrients. Some oxygen minimum zones form naturally, but a much smaller proportion of them."

Eutrophication is the process that occurs when algae grows rapidly due to increased nutrient levels in the water, or put simply, when the water starts to "bloom". Water eutrophication is mainly caused by the excessive loading of nutrients into water bodies, such as nitrogen and phosphorus. According to the researcher, agriculture is a major source of this type of water pollution.

"Transport and industry are also significant contributors, with high emissions of nitrous oxide and nitrogen compounds from combustion. The shipping industry has a particularly negative impact on the environment, with pollution from ships generated by their diesel engines. This explains the global push for alternative options to diesel to make shipping "greener". Similarly, industrial facilities strive to minimise emissions of both carbon dioxide and nitrogen oxides," adds Assoc. Prof. Dr Jokšas.

The key sources of pollution

The VU scientist argues that chemical fertilisers used in agriculture are one of the main contributors to eutrophication in water bodies. Manure and livestock complexes are the other significant producers of nitrogen compounds.

"One of the main issues is that a significant share of the nitrogen and phosphorus is not fully absorbed by plants, and some of it ends up in the underground hydrosphere, rivers, and lakes, and, through tributaries, finds its way to the Baltic Sea, the Curonian Lagoon, or the global ocean, especially when agriculture is developed close to the coast.

Another important source of water pollution is the use of various household products that contain phosphorus compounds. For example, many people use detergents. /.../. Sometimes, the food industry even adds certain phosphate compounds for a variety of specific purposes to improve different foods, etc. Therefore, if household wastewater is not properly treated, it ends up – along with all the mentioned compounds – in rivers and lakes," notes the Associate Professor.

As part of the Green Deal, the EU is looking to step up its efforts to cut water pollution. One of the proposed measures is to prevent fertilisation of fields within a certain distance of water bodies. The EU also aims to increase the efficiency of domestic and industrial sewage treatment.

According to the scientist, this mission is feasible and actively pursued.

How bad might the situation in the Baltic Sea get?

However, Assoc. Prof. Dr Jokšas claims that the Baltic Marine Environment Protection Commission, also known as the Helsinki Commission (HELCOM), which brings together all the Baltic Sea countries, has recently reported that the situation is not improving. Together with the EU, it works to keep the Baltic Sea clean, encouraging the maritime states to carry out research and control, as well as to employ monitoring methodologies, etc.

"Their latest report issued in 2023 shows that the state of Baltic Sea has not improved in 30 years, either in terms of eutrophication or other types of pollution, and the current situation is quite challenging," says the researcher.

HELCOM has adopted the Baltic Sea Action Plan, although similar plans previously bore no fruit. According to Assoc. Prof. Dr Jokšas, one of the main focuses is to minimise pollution from agriculture, i.e. revise agricultural policies, continue to apply certain environmental protection measures, develop buffer zones, and adhere to strict fertilisation plans.

However, the Baltic Sea already shows visible signs of damage. Its high eutrophication caused by human activities and climate change continues to contribute to the expansion of the dead zone. As the water warms and nutrient concentration increases, algae start multiplying more rapidly, algal blooms become denser, and fish populations decline.

Another major challenge is climate change. Rising sea temperatures decrease oxygen solubility. Warming global temperatures lead to heavier rainfall, which allows even more fertilisers to leach into water bodies from the soil, carrying nutrients into the sea and leading to eutrophication processes.

"A key point here is the following: if we curb nitrogen and phosphorus emissions today, we will still have eutrophication in its full swing during the next 30 to 50 years due to the ubiquitous buffer zones. One such accumulation zone with a particularly high concentration of phosphorus can be found in the sediment on the seafloor of the Curonian Lagoon and the Baltic Sea," concludes Kęstutis Jokšas, Associate Professor at the Faculty of Chemistry and Geosciences.