DEAD ZONES

 UPSC GS MAINS IMPORTANT QUESTIONS

What are the consequences of spreading of 'Dead Zones' on marine ecosystem?




Dead Zones are hypoxic(low-oxygen) areas in the world's oceans  and larger lakes. Aquatic and marine dead zones can be caused by the process of Eutrophication, triggered by an excess of plant nutrients ( nitrogen and phosphorous) from fertilizers, sewage, combustion emissions from vehicles and factories.





The nutrients trigger a bloom of phytoplankton at the bottom of the marine food chain, allowing zooplankton to proliferate. As phytoplankton and zooplankton die and sink below the photic zone where photosynthesis can occur, a bloom of natural bacterial degradation exhausts water's dissolved oxygen. 





Dead Zones have spread exponentially since the 1960's and have serious consequences for marine ecosystem functioning. Low oxygen levels recorded along the Gulf Coast of North America have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.





The algae overgrowth blocks the sunlight which hampers the photosynthesis. Lack of sunlight can also lead to death of species in the littoral zones. Dead zones have now been reported from more than 400 systems, affecting a significant proportion of marine ecosystem and probably a key stressor on marine ecosystem.



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