Rising salinity poses threat to sunderbans

Increased frequency of severe cyclones, tidal waves and blocking of freshwater river mouths negatively affect mangrove forests. 
Rising salinity poses threat to sunderbans

NEW DELHI: Tajiuddin Mintu (50), a Basanti Island-based forest conservation volunteer, was jubilant when Finance Minister Nirmala Sitharaman in the Budget 2023-24 announced a special project for mangrove restoration. For more than two decades, Mintu has been conserving mangrove forests in cooperation with the forest department.

He believes mangroves can only save his sinking village Bharatgarh on the island – one of the 54 islands with human settlements and out of 102 islands in India’s Sunderbans, the world’s largest delta. The delta is formed by the confluence of three major rivers – Ganga, Brahmaputra and Meghana, which span around 10 thousand sq km.

India’s mangrove forest, especially Sunderbans Biosphere Reserve, is in crisis due to climate change and anthropogenic activities. Sea-level rises and increased frequency of severe cyclones, which consequently increase salinity, have negatively affected the mangrove forests.

This Budget has tried to address this issue by launching a new scheme named ‘Mangrove Initiative for Shoreline Habitats and Tangible Incomes’ (MISHTI) for taking up mangrove plantation along the coastline.

“MISHTI will give further impetus to our mangrove plantation and conservation efforts,” said Mintu.
Besides acting as bioshields, mangrove vegetation and their associates are also a source of timber, firewood, honey, wax, alcohol and medicinal extracts and herbs.

Diminishing mangrove biodiversity
The increased frequency of severe cyclones, tidal waves and anthropogenic activities such as the blocking of freshwater river mouths to sea are the major cause of the increase in salinity. It leads to change in species composition and sometimes even to their extinction. 

The result of increased salinity is visible on fresh water-loving mangrove trees such as Heritiera fomes (sundari tree), the dominant mangrove species in the Sunderbans. This species is under the endangered category in the International Union for Conservation of Nature (IUCN) Red list. Another mangrove species Nypafruticans (Golpata) is also on the decline.

“Our field observation shows that the density of Sundari and Golpata is reducing fast,” said Ajoy Kumar Das, conservator of forests and joint director, Sunderbans Biosphere Reserve, West Bengal. “Salinity tolerant mangrove varieties such as Avicennia Alba are spreading fast, causing a change in the composition of mangrove forest,” he said.

Das also pointed out the disconnection of principal estuaries of the region to major perennial freshwater rivers such as the Ganga, Brahmaputra and others has accentuated the salinity in the region.
In the recent past, the frequency and severity of cyclonic storms such as Aila, Amphan, Yaas and Bulbul and tidal waves have increased. Tidal waves cause floods and turn the soil more saline and unfit for agricultural activities.

Besides, seawater ingresses to ground water, causing socio-economic problems. “Salinity of agricultural land and underground water has triggered a mass migration from these islands to cities as they either cannot grow crops on this land or are not able to produce enough food to sustain their livelihood,” says Ajanta Dey, Programme Director at NEWS, a non-profit engaged in conservation of mangroves.

Sea-level rise
A detailed study conducted by the West Bengal University of Animal and Fishery Sciences shows that sea-level rising rate in the Sunderbans region is relatively higher than in other parts of the Indian sub-continent, which is causing severe erosion and islands getting submerged rapidly.

“The data of Sagar island for the period of 2002-2009 indicated a rise of Relative Mean Sea Level at the rate of 12mm/year during the decade whereas rest of Indian sub-continent are increasing at the rate of about 2.5 mm/year,” says RK Trivedi, one of the authors of the report. 

However, there is a limit to the plantation of mangroves to counter seal-level rise. For instance, Bhangaduni, Bulcheri and Dalhousie islands are protected mangrove forests and tiger reserves, but half of the islands have been sunken. Moreover, the West Bengal government has increased the area of 85sq km of mangrove plantation in the past three decades. 

Scientists say that plantation has its limitations. Global efforts are required to slow down carbon emissions and stop the melting of glaciers.Meanwhile, in the Sunderbans, Indian and Bangladeshi governments need to collaborate and stop anthropogenic activities such as decommissioning dams that slowed down rivers flow to estuaries. 

“Plantation may not solve the sea-level rise and salinity problems unless you have a whole delta ecosystems rejuvenation plan like fresh river rejuvenation and its flow of sedimentation to delta,” says Sugata Hazra, who used to teach Oceanography at Jadhavpur University.

On the verge of oblivion

Sunderbans Biosphere Reserve: World’s largest river delta consists of 10,200 sq km of mangrove forest, spread over 4,200 sq km in India and 6,000 sq km in Bangladesh

  • Increasing salinity is altering species composition which may even push them to verge of extinction
  • Accelerated sea water ingress has been making ground water unsuitable for consumption
  • Sea level rising in the Sunderbans – higher than in other parts of the Indian sub-continent – has been causing erosion of sandbanks, submerged islands
  • Plantation efforts for mangroves is a solution. However, scientists say that plantation has its own limitations. 
  • There is a limit to the plantation of mangroves to counter rising sea level – with islands already sinking. For instance, Bhangaduni, Bulcheri and Dalhousie islands are protected mangrove forests and tiger reserves, but half of the islands are submerged

Sagar Island, the largest and most populated in Sunderbans, has seen sea level rise at 12mm/year

in the rest of Indian sub-continent sea level is rising at 2.5 mm/year (for the period of 2002-2009)

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