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Oxygen depletion: Danish marine waters severely affected
The inner Danish marine waters have been hit by oxygen depletion this autumn. The phenomenon arose unusually early this year and has been more extensive than normal. It has severely affected the benthic invertebrates in many places. In the short-term this might affect desmeral fish and diving ducks, for which the benthic invertebrates are a food resource. The oxygen depletion is now receding in most areas, and the National Environmental Research Institute expects that oxygen conditions will return to normal during the course of November.
The unusually severe and early oxygen depletion is attributable to the high level of precipitation in January/February and again in June/July combined with a long, calm and warm summer period. Due to the high level of precipitation, nutrient runoff into the fjords and coastal waters has been greater than normal, providing close to ideal conditions for phytoplankton growth. Decomposition of the dead algae has used up the oxygen in the bottom water. At the same time, the lack of strong winds has meant that oxygen input to the water has been minimal. Large amounts of nutrients still continue to runoff into the marine environment, and wind and weather conditions will therefore continue to influence the occurrence of extensive oxygen depletion
Further information: Gunni Ærtebjerg, National Environmental Research Institute. Phone: +45 4630 1260. E-mail: gae@dmu.dk
The reports (English summary) are available at:
http://www.dmu.dk/1_Viden/2_Miljoe-tilstand/3_vand/4_iltsvind/rapporter/rapport.asp
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