Floral life of Sundarbans at stake
By Gazi Anowar , 2017-08-24 11:09:55
Gazi Anowarul Hoque :
The flora and fauna of Sundarbans is at stake due to the increased salinity in the south-west coastal region, which is ultimately damaging the forest ecosystem, say experts and environmentalists.
They said also that the fall of the water level in the Padma that flows towards the Sundarbans through the Gorai-Rupsa-Pashur and the Bhairab-Kobadak tributaries is contributing to the rise of saline in the Sundarbans.
"The mangrove ecosystem of the Sundarbans has the capacity to tolerate a certain level of salinity, but the increased salinity in
the lands is ultimately damaging the forest ecosystem," said Dr Ataur Rahman, Professor of Water Resources Engineering of Bangladesh University of Engineering and Technology.
The saline tolerance of Sundarbans is 10 to 15 ppt (parts per thousand grams) while the current salinity level in the region is around 35 ppt.
He also said that the mangrove forest would be at risk in the future if the salinity level was not reduced to a certain level soon.
Ishtiaq Uddin Ahmed, Country Representative of International Union for the Conservation of Nature Bangladesh, said that two important factors - a certain level of salinity and siltation - are mandatory for the regeneration and sustenance of mangrove ecosystems, but both factors are nonstandard in the case of the Sundarbans in the Bangladeshi regions.
Besides the increased level of salinity, the Sundarbans is being adversely affected by the decreased siltation due to the unplanned establishments of infrastructure, like embankments in the coastal rivers, he added.
A study conducted by biodiversity specialist Dr. Md. Mizanur Rahman says, most of the tree species grown in the Sundarbans cannot tolerate high level of salinity and are seriously affected when salts concentrate within the root zone. Trees are severely affected where groundwater is close enough to the surface to discharge or concentrate salts.
A salt concentration of 20-40% is suitable for mangrove ecosystems, while 40-80% diminishes the number of species and their size. Only a few species can exist and grow in 90% salt concentration. Sundari, Bain, Kakra, Passur and Dhondul tree species are being quickly replaced by Gewa and Keora. Mixed forest stands are being converted into pure stands. The patchily distribution of mangrove date palm (Hanthol) is declining in the fresh swamp and mixed saline forests of Sundarbans.
Another research conducted by Md. Saidul Islam, Department of Geography and Environmental studies of Chittagong University says that approximately one million hectares of land in southern coastal areas of Bangladesh is at risk of salinity. In the recent years, the hydrological conditions have undergone a change in the southwestern part of the country following the commissioning of the Farakka Barrage by India.
At least three reasons are contributing to saline water intrusion: (1) Diversion of Ganges River flow by Farakka Barrage, (2) excessive use of freshwater and (3) Upstream withdrawal for irrigation of rice and others crops.
Abdullah Harun Chowdhury, Professor, Department of Environmental Science of Khulna University, told New Nation recently that the upstream fresh water flow should be ensured, otherwise salinity intrusion would spread.
(This article was published in the daily New Naon on 28th-Jul-2016 )
The writer is a Marine Conservationist based in Bangladesh. He can be reached at email@example.com