The ecosystem of the Sundarban has drastically changed compared with 20 years ago and if it continues the forest will lose almost 29 percent of its productivity. Climate change especially salinity is one of the main reason behind the damage while the numbers of big trees are declining gradually, Dr Swapan Kumar Sarkar, Professor of Forestry and Environment Department, Shahjalal University of Science and Technology was explaining his recent visit of world’s largest mangrove forest, the Sundarban.

In his newly published research paper called Salinity reduces site quality and mangrove forest function. From monitoring to understand Dr Swapan along with other researchers observed that Salt-intolerant climax species like Sundori declined in high saline areas, while salt-tolerant species like Gewa and Goran trees increased.

The mangrove forest is called Sundarbad because of the tree name ‘Sundori’ and the number of the tree has been declining, a threat for the forest, he opted.

Salinity also decreased species-specific leaf area, whereas wood density has been increasing, Dr Swapan said, adding that added, salinity increases significantly impede forest growth, resulting in less productive ecosystems dominated by dwarf species and reducing stand structural properties, soil carbon and macronutrient availability in the soil.

In another researched paper titled solving the fourth-corner problem: forecasting ecosystem primary production from spatial multispecies trait based model Dr Swapan along with two more researchers had applied integrated approach and find that the world’s largest mangrove forest’s ecosystem impacted simultaneously by climate change and multiple types of human exploitation.

The paper also adds that changing seawater levels from the south and freshwater damming from the north cause extensive variations in the Sundarbans' environmental variables, such as salinity and siltation. Environmental drives have an inter-specific availability around a typical functional response to the tree species growing under stress, and this variability depends on the environmental driver’s nature and magnitude.

Muhammad Abdur Rahaman Rana, an environment scientist said "Sundarban is situated on the Ganges estuarine of the triangular shaped Bay of Bengal and the continental shelf of the Ganges estuarine flows to the Bay of Bengal sharply. As a result, brackish water can easily access the coastal areas of Sundarban and its adjacent land areas."

"Brackish water intrusion has increased recently in Sundarban due to sea level rise and exploitation of the natural ecosystem and adjacent water bodies. So, biodiversity of the forest and rivers of the areas cannot tolerate high salinity," he said, adding that almost 195 species of different fishes, trees, flora and fauna have already faced extinction from the Sundarban areas.

Meanwhile, brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with freshwater, as in estuaries, or it may occur in brackish fossil aquifers.

Abdur Rahaman, who is the Director of Center for People and Environ also said that fresh water fishes are declining fast in Sundarban while some of them migrated themselves from the area as the salinity is likely to adversely affect their reproductive cycle and capacity, extent of suitable spawning area and their feeding and breeding.

According to World Bank Report, the different salinity tolerance ranges for 14 varying dominant mangrove species detected in 2013 satellite images of the Sundarban with the expected salinity for alternative scenarios of climate change by 2050.

The report also relieved that the Sundarban's ecosystem induced by rising salinity are likely to change the prospects for forest and fishery-based livelihoods, resources should be directed to the development of alternative livelihoods for ecosystem-dependent households.

Accusing increasing salinity for losses of livelihoods and several fishes, Mohon Kumar Mondol, Executive Director of Local Environment Development and Agricultural Research Society (LEDARS) said salinity put the lives under risk not only of biodiversity but also of humans and their livelihood.

People are compelled to migrate in other cities because of salinity and alternative employment, he said, adding that some tube-wells and ponds are the main sources for freshwater but those are insufficient for the area. Soil salinity is likely to lead to a significant decline in the output of high-yielding varieties of rice which ultimately impacts on the poor farmers' livelihood. He added.

Mondol also said that the Government has allocated a budget to the Union Parishad under the Ministry of Local Government, Rural Development and Co-operative for development. Some rainwater collecting projects are under pipeline but those need to be implemented very soon as the situation deteriorates gradually.

BDST: 1741 HRS, APRIL 26, 2023
MSK