Baltic Sea
The Baltic sea dead zone is considerably the world's largest dead zone. The Baltic Sea's sensitive waters have been overwhelmed by phytoplankton, which are depleting the oxygen levels and suffocating marine life. The hypoxic zone was discovered over the last 40 years and is now home to world's ten of the largest marine dead zones. The Baltic Sea is a large and almost entirely closed marine region with both salt and fresh water. The Danish straits through to the North Sea is its only connection to the ocean. Since the sea is surrounded by a huge drainage area, it is most likely that human activities have influenced the formation of the dead zone.
Save Our Baltic Sea. (2014). About the Baltic Sea. Available: http://www.saveourbalticsea.com/index.php/our-baltic-sea/about-the-baltic-sea. Last accessed 25th March 2014.
Save Our Baltic Sea. (2014). About the Baltic Sea. Available: http://www.saveourbalticsea.com/index.php/our-baltic-sea/about-the-baltic-sea. Last accessed 25th March 2014.
Figure 8:
Figure 8 is a satellite image made courtesy by Jeff Schmaltz that was taken in July 2005 and it depicts the world's largest dead zone in the Baltic Sea. The dead zone can be recognized the lighter swirls in the sea which displays algal blooms and eutrophication. As seen in the image, the hypoxic area expands over a vast area.James Owen. (2010). World's Largest Dead Zone Suffocating Sea.Available: http://news.nationalgeographic.com.au/news/2010/02/100305-baltic-sea-algae-dead-zones-water/. Last accessed 25th March 2014.
Figure 8 is a satellite image made courtesy by Jeff Schmaltz that was taken in July 2005 and it depicts the world's largest dead zone in the Baltic Sea. The dead zone can be recognized the lighter swirls in the sea which displays algal blooms and eutrophication. As seen in the image, the hypoxic area expands over a vast area.James Owen. (2010). World's Largest Dead Zone Suffocating Sea.Available: http://news.nationalgeographic.com.au/news/2010/02/100305-baltic-sea-algae-dead-zones-water/. Last accessed 25th March 2014.
Causes
About nine countries are found along the Baltic Sea, making it extremely vulnerable to human activities. Where there are large populations of humans, there is usually industrialization and extensive practices of agriculture. The Baltic Sea has been affected by huge amounts of algal blooms, which are caused by excess inputs of nitrogen and phosphorus which come from many sources. Mainly agricultural fertilizers and sewage cause the nutrient enrichment and the dead zone to eventually form. The huge drainage area that surrounds the sea consists of large areas of farmland. When downpours occur, the excess fertilizers run-off from the land and enter the Baltic Sea. Urban waste waters that are being dumped into the Lake also increase the risk of eutrophication.
Overfishing had also been proved to contribute the formation of dead zones. The Baltic Sea home to a huge population of cod, whose purpose is to eat sprats, which are small herring like species. The sprats eat zooplankton which in turn feeds on algae. This is a food chain which becomes disrupted due to overfishing. By excessively removing cod from the sea , it would effectively increase algal blooms, because the population sprats are not being controlled by the cod. This results in less zooplankton and an explosion of algae growth which deplete oxygen levels and ultimately cause dead zones to form.
This is an animation of an example of how agriculture caused eutrophication and dead zones:
Animation_
SOBS. (2009). Baltic Sea Dead Zones. Available:
http://www.saveourbalticsea.com/index.php/baltic-sea-dead-zones. Last accessed
23rd March 2014.
Overfishing had also been proved to contribute the formation of dead zones. The Baltic Sea home to a huge population of cod, whose purpose is to eat sprats, which are small herring like species. The sprats eat zooplankton which in turn feeds on algae. This is a food chain which becomes disrupted due to overfishing. By excessively removing cod from the sea , it would effectively increase algal blooms, because the population sprats are not being controlled by the cod. This results in less zooplankton and an explosion of algae growth which deplete oxygen levels and ultimately cause dead zones to form.
This is an animation of an example of how agriculture caused eutrophication and dead zones:
Animation_
SOBS. (2009). Baltic Sea Dead Zones. Available:
http://www.saveourbalticsea.com/index.php/baltic-sea-dead-zones. Last accessed
23rd March 2014.