Wetlands just outside India’s Kolkata city have been a source of food and employment for generations. They filter sewage through fish ponds, providing tonnes of food daily and thousands of jobs.
However, the rapid urbanisation of the area is now threatening this ecosystem.
Conservationists are warning that pollution and forceful land grabs are putting the lifeline for the megacity’s 14 million residents at risk.
“We are destroying the environment,” said Tapan Kumar Mondal, a fish farmer who has spent his life working in the canals and ponds that stretch across about 125 square kilometres (48 square miles).
“The population has increased, putting pressure on nature and ruining it,” added the 71-year-old.
The wetlands are listed as a wetland of global importance under the United Nations Ramsar Convention. They offer natural climate control by cooling sweltering temperatures and act as valuable flood defences for low-lying Kolkata.
However, Dhruba Das Gupta from the environmental group SCOPE said that short-sighted building development is encroaching on the wetlands.
“The wetlands are shrinking,” said the researcher, who is trying to secure funding for a study on what remains of the waters.
Every day, 910 million litres of nutrient-rich sewage flow into the wetland, feeding a network of about 250 hyacinth-covered ponds.
“Sunlight and the sewage create a massive plankton boom,” explained K Balamurugan, chief environment officer for West Bengal state. He added that the microorganisms in the shallow fish ponds feed rapidly growing carp and tilapia.
Once the fish have consumed their share, the water run-off irrigates surrounding rice paddies, and the remaining organic waste fertilises vegetable fields.
“The sewage of the city is being naturally treated by the wetlands,” said Balamurugan, giving them the nickname the “kidneys of Kolkata”.
The community-developed system was created by “the world’s foremost connoisseurs of wastewater wise use and conservation,” according to its UN Ramsar listing. However, the listing also warns that the wetlands are under “intense encroachment stress of urban expansion”.
According to a 2017 University of Calcutta study, the wetlands system processes about 60 percent of Kolkata’s sewage free of charge, saving the city more than $64m a year.
Original from www.aljazeera.com