Anoxia Threatens Kochi Backwater Ecosystem

Problems such as decrease in the flow of water, deepening of channels, anoxia (total depletion in the level of oxygen) and denitrification is plaguing Kochi backwaters

Published: 23rd October 2014 06:03 AM  |   Last Updated: 23rd October 2014 06:03 AM   |  A+A-


KOCHI: The backwaters in Kochi are being suffocated to death. Problems such as decrease in the flow of water, deepening of channels, anoxia (total depletion in the level of oxygen) and denitrification is plaguing Kochi backwaters. All this has lead to the formation of greenhouse gases like hydrogen sulphide and nitrous oxide in the bottom waters of Kochi. The study titled ‘Formation of anoxia and denitrification in the bottom waters of a tropical estuary, southwest coast of India’ was done jointly by National Institute of Oceanography and CUSAT in 2010 and the detailed report was published in 2014.

“The formation of anoxia in the bottom waters of lower Kochi backwaters has been reported for the first time in the estuaries along the West coast of India. The decreased movement of water and deepening of channels has probably reduced the natural flow and increased intrusion of upwelled coastal waters. The intrusion of the upwelled waters from Arabian Sea to Kochi backwaters has lead to further oxygen depletion due to weak flushing along with high organic input from anthropogenic

loadings. This anoxia ultimately leads to denitrification and oxygen becomes less available for many organisms that live near the surface of the water, and this may be a reason for their exclusion from this zone,” the study states.

Experts see red in this situation and point out that rapid economic growth makes the region’s coastal environments highly vulnerable.

“In view of the rapid development of the region and population upsurge (expected to cross fifty lakh by 2025) proper environmental conservation plans to minimise pollution and counter developmental impacts that are inevitable needs to be put in place,” the study points out.

“The prevalent upwelling in the Arabian Sea brings cool, saline, oxygen deficient and nutrient-rich waters towards the coastal zone and bottom layers of Kochi backwaters during

the high tide. Intrusion of Arabian Sea waters seems to be stronger in the upstream end, than previously reported. This due to the lowering of river discharges and deepening of channels in the estuary. Increased stratification coupled with low ventilation and presence of high organic matter has resulted in anoxic condition 2-6 km away from barmouth of the estuary and this leads to the formation of hydrogen sulphide. The expansion of oxygen deficient zone, denitrification and formation of hydrogen sulphide may lead to a destruction of biodiversity and an increase in green house gas emissions in this region,” said G D Martin, who was a member of the study team.

Kochi backwaters are known for their rich bio-resources, but its pristine condition has suffered severly due to human intervention, the report said.

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