Hypoxia in the Baltic Sea hits the coastal zone
New study shows that the spread of dead zones in the Baltic Sea have reached the coastal zone.
115 sites have been identified during the period 1955 - 2009, with the Baltic Sea coastal zone containing over 20% of all known sites worldwide.
Spread of Baltic Sea dead zonesHypoxia in off-shore deep waters of the Baltic Sea is well-described, but knowledge of coastal zone hypoxia has previously been lacking. The new study, compiling coastal monitoring and research data from Baltic Sea countries using the Baltic Environmental Database (BED), show that the dead zones in the Baltic Sea have now also reached the coastal zone.
Lead author Daniel Conley reports to Swedish Television "I am very worried, we never expected to see so many coastal areas with hypoxia. Hypoxia removes the habitat for fish, and they have much smaller areas that they can live in because the deeper areas are devoid of oxygen. Unfortunately things appear to be getting worse, these dead zones are spreading in the coastal areas".
The researchers found at least 115 sites along the Baltic Sea coast where hypoxia occured. On 32 sites, the level of oxygen have decreased during the last 50 years, 10 sites showed improvement in oxygen content, while 76 sites showed no trend.
Baltic Sea hypoxia
Hypoxia is devastating to ecosystems, threatening benthic communities and potentially reducing biodiversity, as animals are unable to survive in these “dead zones”. Research show that the increase of the spatial extent and intensity of hypoxia is coupled to anthropogenic eutrophication.
Hypoxia is common in estuaries
located in the Danish Straits due to the large load of nutrients
sustaining algal production and the strong stratification caused by
large differences in surface and bottom water salinity. Hypoxia
in the Swedish and Finnish archipelagos are influenced by
phytoplankton growth stimulated by nutrient loads from urban
and agricultural sources, but also by restricted water circulation. By contrast, hypoxia is rare in the
northern Baltic Sea estuaries located in the Bothnian Sea
coastal zone where nutrient loads are lower. Hypoxia is
uncommon along the eastern shore from Estonia to Poland
due to enhanced circulation of water in open areas along the
Research have identified the Baltic Sea as home to the world's largest anthropogenic "dead zone", with hypoxia, (i.e. oxygen depletion) representing a marked decline in water quality. The coastal zone displays an alarming trend with hypoxia steadily increasing with time since the 1950s effecting nutrient biogeochemical processes, ecosystem services, and coastal habitat. Including the sites found in the new study, the Baltic Sea coastal zone now contains over 20% of all known hypoxia sites worldwide.
Read more about the new study.
Swedish media coverage on the study was extensive, including the following coverages in SVT, Sveriges Radio, DN, Göteborgs Posten, TV4, Hela Gotland, Skånskan.
The Baltic Nest Institute have published numerous articles on hypoxia, which can all be found on our publication list, as well as being a major partner of the HYPER-project.