The vast mangrove forest in the Sunderbans is fast losing its capacity to absorb carbon dioxide, one of the main greenhouse gases, from the atmosphere due to rise in the salinity of water, rampant deforestation and pollution, a study has found.

The mangrove forest, marsh grass, phytoplanktons, molluscus and other coastal vegetation in the world’s largest delta are the natural absorbers of carbon dioxide (CO2), according to the study.
The stored carbon in the plants is known as “Blue Carbons”. The absorption of CO2 is a process which contributes to reduction of the warming of the earth and other ill effects of climate change.
The research study, “Blue Carbon Estimation in Coastal Zone of Eastern India — Sunderbans”, was financed by the Union government and headed by noted marine scientist Abhijit Mitra.
The report took three years to prepare and it was submitted to the government last year.
The scientists involved in the study have sounded an alarm bell, especially in the central Sunderbans, one of the three zones into which the forest was divided for the study, the other two being western and eastern.
“The situation is quite alarming, especially in the central part. The capacity of the mangrove forest, especially the Byne species, to absorb carbon dioxide has eroded to a large extent. This will affect the entire ecosystem of the area,” Sufia Zaman, a senior marine biologist who was a part of the team, told PTI.
According to Mitra, the study was conducted mainly on the Byne species of mangrove. There are 34 other species of mangroves found in the forest including Keora and Genwa.
In the central part of Sunderbans near Matla, the capability of Byne trees to absorb carbon was 22 tonnes per hectare, whereas the scenario is a bit different in the eastern Sunderbans where the capacity of Byne to absorb carbons is near about 35 tonnes per hectare,” Mitra said.
Mitra felt that the situation was fraught with danger because less absorption of CO2 from the atmosphere meant higher proportion of CO2 in the atmosphere which traps heat.
Comparing the situation with mangrove forests in Indonesia and Vietnam, Mitra said, “In Indonesia, the absorption capacity of carbons is 114 tonnes/hectare whereas in Vietnam the quantity is 80—90/tonnes per hectare.”
Going into the reasons for the scenario in the Sunderbans, a UNESCO world heritage site, Mitra said, “One of the main reasons is a sharp rise in the salinity of water in Matla river.”
“The mangroves grow on fresh water, but because of lack of fresh water the height of mangroves has come down substantially, reducing its capacity to absorb carbons,” he said.
He points out that as fresh water is available in eastern Sunderabans, the trees there are taller.
Owing to deposition of silt at the confluence of the Vidyadhari and Matla rivers, fresh water is unable to enter the Matla river, giving rise to its salinity, he says.
“The other reasons are shrimp farming, mushrooming of brick kiln industry and deforestation which together have added to the reduced growth of Byne mangroves,” Mitra said.
He explained that the situation was better in the eastern Sunderbans where there was less human incursion as well as in the western part which was fed by a regular supply of fresh water from the Hooghly river.
According to Mitra, if steps are not taken to remove the silt deposits at the meeting point of the Vidyadhari and Malta rivers, the situation may get worse. He suggested dredging of the channel and afforestation besides checking shrimp farming.