Salt water encroachment is increasing in Sundarbans, biodiversity is under threat of that
Saltwater encroachment is increasing in the Sundarbans, the world’s most notable mangrove forest. The flow of fresh water is decreasing in this forest marked as world heritage. As a result, freshwater-dependent trees and fish are dying. Forest biodiversity is being altered by excessive salinity.
Experts believe that the withdrawal of water from the source or upstream of the rivers that flow through the Sundarbans is the main cause of this problem. Climate change has been added as a new threat. Less salt-tolerant plants are dying as salinity increases. Climate change causes rising sea levels, leading to increased tidal water height. This, in turn, results in the sinking of forest lands and a decrease in soil bonding. Erosion also causes the forest to shrink.
Sundarbans researcher and writer Gaurang Nandi said that many rivers, including one of the main animal rivers of Sundarbans, Shibsa River, Raimangal River, Kapotaksha River, have dried up and died. Many small rivers and canals have died and dried up.
The rivers in the Sundarbans region were separated long ago from the northern rivers; Ganges, Padma, Garai survived a little. However, the construction of the Farakka Barrage also caused obstacles in that regard. An increase in the flow of fresh water upstream will reduce the flow of salt water.
Environmental Science Discipline (Department) of Khulna University researched the salinity of various rivers in Sundarbans in 2020. The results show that the maximum salinity in the Pasur River during the dry season in 2020 was 22.6 ppt (parts per thousand). Although in 2010 it was 17.5 ppt.
The researchers said that rivers in coastal areas generally have a salinity of two to five ppt. Climate change has caused the Sundarbans water and soil to become too salty due to rising sea levels and reduced freshwater flow from upstream.
The alluvium has increased by leaps and bounds. In 2013, the amount of silt in Harbaria area of Pasur river was 9 cm. In 2019-20 it stood at 22 cm. In the Karamjal area of the river, there was 19 cm of silt a decade ago, but now it has increased to 39 cm.
Due to climate change, the water level of various rivers in the forest is increasing. Recently, most of the forest land near the Shibsa river in the Sundarbans was found to be submerged during high tide.
The same situation is seen in the forests of Arua, Shibsa, Andharmanik River, Bajbaja, Shakbaria river banks. Numerous trees have been uprooted on the banks of Shivsa, Morjat, Arpangashia, Hansraj rivers.
ASM Helal Siddiqui, Khulna Divisional Officer of the Forest Research Institute said, they divided the Sundarbans into low, medium and high salinity areas. But recent studies have shown that the forest has become highly salinized everywhere. Seedling growth rate of 10 plants, including less salt-tolerant plants, has decreased.
Forest trees are affected by various diseases. On the other hand, Gewga tree is growing a lot. In 1985, 16 percent of the forest was Gewga trees, but now 50 percent of the forest is Gewga trees. Deer or other animals do not eat the leaves and seeds of the Gewga tree plant because of the salty gum. It also affects wildlife.
The officer Tanmoy Acharya from the Forest Department mentioned that creepers are not growing as much as before in the forests near the wetlands. More research is needed to understand how salinity increase affects wildlife and to take effective measures in this regard.
