The global science community is watching the problem of oxygen depletion in marine and coastal areas with growing concern. Over the last few years the number of known dead zones globally has increased from 44 in 1995 to 169 according to a recent report from the World Resource Institute (WRI).
The global science community is watching the problem of oxygen depletion in marine and coastal areas with growing concern.
Over the last few years the number of known dead zones globally has increased from 44 in 1995 to 169 according to a recent report from the World Resource Institute (WRI). Another 246 areas are considered “vulnerable”.
The report also concludes that there is still insufficient information available to determine the real extent of the problem in many parts of the world.
WWF notes that together with overfishing and climate change, the growing number of dead zones is among the biggest threats to the world’s oceans in the 21st century.
Marine dead zones are caused by eutrophication – a process where bodies of water receive excess nutrients, mainly nitrogen and phosphorus. Dissolved in the water, the nutrients act as fertilisers and thereby enhance plant growth.
The dead zones occur when algae and other organisms die, sink to the bottom, and are decomposed by bacteria, using the available oxygen. Agriculture, human sewage, urban runoff, industrial effluent, and fossil fuel combustion are the most common sources of nutrients delivered to coastal systems.
“The situation is alarming – but a complete picture may be even worse”, says Jochen Lamp of WWF Germany, author of the briefing paper.
“Eutrophication is an issue that requires greater attention by governments and society in general. Left untouched, it may have dire consequences for many ecosystems, the food webs that they support, and the livelihoods of the populations that depend on them.”
According to one of the WRI scientists, Robert Diaz, 7 of the 10 largest dead zones recorded in their latest report are found in the Baltic Sea.
An assessment made by the Helsinki Commission (HELCOM) estimates these to cover an area of 42,000 km².
In some periods they can easily reach up to 90.000 km².
Other hotspots of oxygen depletion are found in the Gulf of Mexico, the Black Sea and the Adriatic Sea.
Around 4/5ths of the US coast and 2/3rds of Europe’s coasts are now faced with excessive eutrophication. Experts also believe that there are numbers of yet unexplored dead zones in the coastal waters of China and Southeast Asia.
Dead zones can also further add to the problem of eutrophication in the Baltic Sea in a vicious circle. Normally, phosphorus slowly binds to the sediments on the sea bottom and is thereby removed from the water. When there is no oxygen left in the sediments, these compounds are transformed and the phosphorus is released back into the water.
“Most people now connect eutrophication with the yearly algal blooms that we are now used to seeing each summer”, says Mats Abrahamsson from WWF. “For the Baltic Sea, these dead zones are an invisible but even larger problem over the longer term. Dead zones can lead to the collapse of whole ecosystems as bottom-dwelling organisms die and more phosphorus is released into the water.”
WWF believes that governments must take the consequences of eutrophication seriously.
As agriculture contributes to about 50% of the excess nutrients in the Baltic Sea, WWF advocates a reform of agriculture policy to curb these emissions.
- Baltic Sea environment and conservation
- Eutrophication and Hypoxia in Coastal Areas: A Global Assessment of the State of Knowledge
For more information, please contact:
Mats Abrahamsson, WWF Baltic Ecoregion Programme, Programme Director, tel: +46 705 821 499
Jochen Lamp, WWF Germany, Head of Baltic Sea Project Office leader, tel: +49 3831 297 018