The wetlands outside India’s Kolkata have for generations provided tons of food every day and thousands of jobs as they filter sewage into fish ponds—but rapid urbanization threatens the ecosystem.
Conservationists warn that pollution and rampant land grabbing are putting a lifeline for the megacity’s 14 million residents at risk.
“We’re destroying the environment,” said Tapan Kumar Mondal, who has spent his life farming fish in a clever system of canals and ponds spanning about 125 square kilometers (48 square miles).
“The population… has increased, there is pressure on the environment, they are destroying it,” added Mondal, 71 years old.
Listed as a wetland of global importance under the United Nations Ramsar convention, the bodies of water offer natural climate control by cooling hot temperatures—and act as important flood defenses for lower Kolkata. .
But Dhruba Das Gupta, from the environmental group SCOPE, said short-sighted building developments were encroaching on the wetlands.
“The wetlands are shrinking,” said the researcher, who is trying to finance a study on what remains of the waters.
Every day, 910 million liters of nutrient-rich sewage flows into the swamp, feeding a network of about 250 hyacinth-covered ponds.
“Sunlight and pollution create a huge plankton boom,” said K. Balamurugan, chief environment officer in the state of West Bengal, explaining that microorganisms in shallow ponds of fish feeds on fast growing carp and tilapia.
When the fish are full, the runoff water irrigates the surrounding rice paddies and the remaining organic waste fertilizes the vegetables.
“The sewage of the city is treated naturally in the wetlands,” says Balamurugan, giving them the nickname “Kolkata’s kidneys”.
The community-developed system was created by “the world’s foremost connoisseurs of wastewater wise use and conservation”, according to its UN Ramsar listing, which also warns that it is under “severe encroachment stress of expansion in the city”.
The late ecologist Dhrubajyoti Ghosh, who played a key role in the 2002 Ramsar submission, called Kolkata an “ecologically-subsidized city”.
The sewage system processes about 60 percent of Kolkata’s sewage free of charge, saving the city more than $64 million a year, according to a 2017 University of Calcutta study.
Wetland farms provide about 150 tons of vegetables per day, 10,500 tons of fish per year and employ tens of thousands of people, the Ramsar list estimates.
For Kolkata, in the vast delta where the Ganges River meets the Indian Ocean, the wetlands also provide flood defenses for a city facing rising sea levels due to climate change.
“This city never faced any flooding issue,” added Balamurugan. “These wetlands act as a natural sponge, absorbing excess rainwater.”
Das Gupta said the biodiversity hotspot also “plays an important role in climate stabilization”, calling the wetlands “the lifeline of Kolkata”.
“Wetlands should remain, because of the cooling they achieve through their presence,” he said.
‘The land was seized’
But the Ramsar list says that industrial effluent pollutes natural systems, threatening food production.
Fish farmer Sujit Mondal, 41, said that compared to last year “production has decreased” due to “murky water”.
About 95 percent of the wetlands are in private hands.
As land prices rise, environmental officials say they are pleading with people not to fill in fish ponds to make room for new construction.
“We ask not to convert the wetlands, not to exchange these wetlands for buildings, not to fill them,” said Balamurugan.
But residents say village councils are being hired by land-hungry developers.
“They are often accused by residents of giving informal permission in exchange for money to real estate developers to build, while they look the other way,” said Das Gupta.
“This leads to a large loss of productive space, and destroys the ecosystem services offered by these wetlands,” he added.
“The land is being taken away from the people,” said Sujit Mondal, the fish farmer.
Gangs even net the ponds at night to steal the fish, leaving farmers with little choice but to close and sell.
“They are forcing the fishermen to give up their livelihoods,” Das Gupta said. “Then they will control the land.”
© 2023 AFP
Citation: The ‘kidneys of Kolkata’: Indian wetlands under threat (2023, July 18) retrieved 18 July 2023 from https://phys.org/news/2023-07-kidneys-kolkata-indian-wetlands-threat.html
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