The biggest problem in the Baltic Sea is anthropogenic eutrophication, or enrichment with nutrients

The Baltic Sea is one of the seas most influenced by human activity in the world. The Baltic Sea basin (the area from where water flows into the sea), four times the size of the sea itself, is home to more than 85 million people. Therefore, the pollution load on the sea is quite high. Given the geomorphological features of the Baltic Sea (e.g. low and narrow connections to the ocean and slow water exchange), its ability to offset negative pressures from human activities and other factors is rather limited. The Baltic Sea is therefore very sensitive to all kinds of changes and pollution. 

Today, the most important environmental problems in the Baltic Sea are the enrichment of seawater with nutrients and pollutants, the overcatching of fish, and the introduction of alien species. Intense shipping and the resulting threats (including alien species and oil pollution) are also major pressure factors. In addition, the problems of marine litter and drug residues, which have been addressed more and more recently, cannot be overlooked.

The biggest problem is eutrophication

The biggest problem in the Baltic Sea is anthropogenic eutrophication, or enrichment with nutrients. This has led to an increase in algal biomass, for example, or algal blooms, which increase the turbidity of the water. This, in turn, increases oxygen consumption near the seabed and can lead to oxygen loss. These conditions lead to changes in the species composition and abundance of the benthos [1]. The main cause of the eutrophication in the Baltic Sea is the inflow of nitrogen and phosphorus from land-based sources, which reach the Baltic Sea via rivers [2]. Another major problem is the various pollutants that reach the sea through both rivers and the atmosphere. The assessment of the state of the Estonian marine environment [3] confirms that the amounts of nutrients in the Baltic Sea are too high and the water status on the basis of this indicator is unsatisfactory. Organic compounds are found in sediments (for example in the Tallinn, Haapsalu, and Pärnu areas) as well as in fish in small concentrations.

The microbiological quality of the Estonian coastal waters in the Baltic Sea is affected by point source pollution (waste water and rain water discharges), diffuse pollution (flush water and rain water from land), and, taking into account the growing popularity of cruise ships, faecal pollution from ships (untreated or partially treated faecal water being released into the sea, pollution from ports). The most important sources of the pathogens of the coastal sea are the waste water discharges from medical facilities [4].

The Estonian marine fish stocks are relatively diverse, but also under strong human influence. The main anthropogenic pressures are fishing, agricultural, household, and industrial pollution, and the resulting eutrophication, as well as the invasion of alien species. At least 35 alien species have been found in Estonian seawater over time [5]. Increasing shipping traffic, combined with climate change, is encouraging the spread of alien species. The area with the highest initial invasion risk (the area where new alien species are most likely to be detected) in Estonia is the area around Tallinn, especially the Muuga Bay with its large port.

The impact of fishing on populations is the removal of large quantities of mature fish from the population. As a result, the structure of the stock is changed, with the average length, individual body weight, and age of the fish in the population decreasing. At the same time, the impact of fishing in the Estonian coastal sea on non-target species (species that get caught in traps, although they are not the species the traps are set for) mainly concerns seals and water birds, as the most important fishing gear is various fixed gear [5].

The state of the coastal sea is assessed on the basis of the EU Water Framework Directive. The environmental status under the Water Framework Directive consists of two aspects: ecological status and chemical status. The ecological status consists of the status of aquatic organisms (benthic flora, benthic fauna, phytoplankton) and the status of other indicators affecting it (hydromorphology, water quality, content of pollutants in water). The chemical status is assessed based on the concentrations of priority substances. As of 2022, the ecological status of most of the Estonian coastal sea is moderate (63%), 19% of the coastal sea is in a good state, 13% is in a poor state and 6% is in a bad state. The chemical status is poor everywhere. The overall status of Estonian coastal waters as of 2022 is bad in one body of water and poor everywhere else [6].

The impact of climate change

Major changes, including changes in atmospheric processes due to climate change, are directly reflected in the seawater circulation, temperature, and salinity regime. The projected increase in temperature and precipitation in the climate scenarios, as well as the acidification of seawater and the increase in storms, will lead to changes in different directions. The intensification of overgrowth, the invasion of southern species, and the decline of key cold-loving species will affect the biodiversity and balance of the marine environment. In addition, climate change will lead to changes in food chains, a longer growing season, and an increase in overall biomass production. The exact impact of the latter changes on the various processes and the overall functioning of the marine environment is unknown [7].

Last modified: 17.11.2023

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[1] R. Aps, M. Kangur, E. Ojaveer, T. Saat. Läänemere loomastik. Eesti Entsüklopeedia, 2002; 2011.
http://entsyklopeedia.ee/artikkel/l%C3%A4%C3%A4nemere_loomastik 
[2] R. Roasto jt. Eesti looduse kaitse aastal 2020. Tallinn: Keskkonnaagentuur, 2020
[3] A. Lotman, G. Martin, K. Viik, U. Lips (toim). Eesti mereala keskkonnaseosund 2018. Tallinn: Keskkonnaministeerium.
[4] K. Künnis-Beres, I. Lips. Merevees esinevate võimalike patogeenide pilootseire. Aruanne, 2018
[5] G. Martin. Eesti mereala keskkonnaseisundi esialgne hindamine. Aruanne EL-i merestrateegia raamdirektiivi artikkel 8-st tulenevate riiklike kohustuste täitmiseks. TÜ Eesti Mereinstituut, 2012. 

[6] Pinnavee ja põhjavee seisund - interaktiivne kaart. Keskkonnaagentuur. https://kaur.maps.arcgis.com/apps/MapSeries/index.html?appid=fd27acd277084f2b97eee82891873c41
[7] BioClim. Kliimamuutuste mõjuanalüüs, kohanemisstrateegia ja rakenduskava looduskeskkonna ja biomajanduse teemavaldkondades. Lõpparuanne. Tartu: Eesti Maaülikool, 2015, lk 28.