Rising salinity threatens Sundarban
Decreasing flow of water through the rivers from upstream is
destroying the ecosystem of Sundarban.
Experts from home and abroad observed that alarming decrease in water
flow down the rivers caused high salinity in both water and soil of
Sundarban, causing a massive change in faunal composition of the
forest.
Sundarban, which lies across the outer deltas of the Ganges,
Brahmaputra and Meghna rivers, is the largest mangrove forest in the
world.
Some 40 per cent of the total 10,000 square km forest is in India and
60 per cent in Bangladesh.
A quarter of the total forest in Bangladesh and India has been
designated as World Heritage sites by UNESCO.
The latest report of World Conservation Monitoring warned that a
long-term ecological change is taking place in Sundarban due to the
eastward migration of the Ganges, abandonment of some distributaries
and past diversion of water and withdrawals for irrigation,
The report further observed that diminished fresh water flushing of
Sundarban has resulted in increased saline intrusion, particularly in
the dry season.
The Sundari trees grow and survive where the soil water is relatively
fresh, especially in the northeast, and on higher ground, and form 60
per cent of the commercially useful timber. The reason for the
difference is the strong influence of freshwater, the report said.
Recently, the World Bank has commissioned five reputed organisations
for conducting studies under its ongoing study named Climate Change
Adaptation, Biodiversity Conservation and Socio-Economic Sustainable
Development for the Sundarban Area of Bangladesh.
The International Union for Conservation of Nature (IUCN) has been
commissioned to do 'Strategic Management Plan for Sundarban's
Biodiversity' as part of the World Bank's study.
After the mid-term report of the study, Md Istiak Sobhan, progrmme
co-ordinator of IUCN, told New Age, 'Increase of salinity in water and
soil of Sundarban is changing faunal composition. The number of timber
producing big trees such as Sundari is decreasing at the proportionate
rate at the increase of salinity,'
'Sundari is found half where salinity is doubled from 10ppt to 20ppt.
Even the size of the Sundari becomes dwarf in such moderate saline
areas. And in the high saline areas in the south-west part of the
forest, where salinity is over 30ppt, no Sundari exists,' he added.
According to Sobhan, salinity started to affect the Sundari trees
since 1950s. But the rate of the damage of the timber producing
mangrove forest accelerated after the construction of the Farakka
barrage in 1975.
Huge damage of Sundari trees was evident from 1975 to 1997 due to
indiscriminate withdrawal of upstream water at the Farakka, Sobhan
pointed out.
The eastern part of Sunderban gets moderate fresh water through the
Baleswar River, a distributary of the Meghna river, he said.
In the past, Sundarban had experienced a balanced growth of flora and
fauna due to fresh water flow from the upper stream Ganges at the
north and the salty water inflow from the Bay of Bengal in the south.
But the balance is now being threatened due to decreasing freshwater
flow from upstream, experts pointed out.
'As the salinity of Sundarban increases from east to west, density of
vegetation growth and canopy closure decreases from east to west.
Height and growth of different species in Sundarbans are related with
the salinity,' reads the paper presented by Syed Azizul Haq,
superintending engineer of the Public Works Department, who read the
paper in the 18th commonwealth forestry council held in Edinburgh in
2010.
Three height classes have been recognised in Sundarban in the study
carried out by Center for Environmental and Geographic Information
Services. The height of the forest is greater in the east. The height
decreases as one proceeds towards the west, adds the study done by
CEGIS for the ministry of forestry and environment.
'Sundari tress grows in the areas where salinity is only five to 10
parts per thousand (ppt). Gewa grows basically in the moderate saline
water of 10-25ppt. And low height Goran grows in high saline zones of
over 25ppt,' Ahmadul Hassan, senior water resources planner of CEGIS,
told New Age.
Not only the Bangladeshi experts, the Indian experts also have similar
observation that the Sundeban mangrove forest is in great threat due
to salinity intrusion.
Abstract from a paper on 'Biodiversity and its Conservation in
Sundarban Mangrove Ecosystem' by Indian scholars Brij Gopal and
Malavika Chauhan published in the Aquatic Science journal revealed
that the regulation of river flows by a series of dams, barrages and
embankments for diverting water upstream for various human needs and
for flood control caused large reduction in freshwater flow and
seriously affected the biodiversity because of an increase in salinity
and changes in sedimentation.
The poor flows of tidal and freshwater result in high salinity of
mangrove swamps and thus reduces the growth of mangroves, observes
professor K Kathiresan of Centre of Advanced Study in Marine Biology,
Annamalai University, in his article titled Degradation and
Destruction of Mangroves.
'At least 100 cubic metres per second (cumec) water flow is required
through Gorai channel to protect the biodiversity in Sunderban, which
at present gets less than 30 cumec during the dry season,' observes
Ahmadul Hassan of CEGIS, who is at present conducting a Socio-economic
study of Sunderban as part of the World Bank's ongoing study project.
Many hydrologists and environmentalists believe that the proposed
Ganges Barrage Project to divert the flow of Ganges to the Gorai river
during dry seasons can be a good option to solve the problem.
Diversion of about 200 cumec water flow through Gorai river system,
particularly during critical dry period of April, will push the 1ppt
saline line by 45km seaward, reveals a study on Impact of Climate
Change on Coastal Community of Bangladesh conducted by the Institute
of Water Modeling (IWM).
Hydrologists believe the minimum share of 1000 cumec water mentioned
in the Ganges Water Treaty (GWT) of 1996 must be ensured. Otherwise,
they said, diversion of 100 cumec water through Gorai channel would
kill the Padma River system in the downstream.
Environmentalists consider it a positive move that Indian and
Bangladesh prime ministers are scheduled to sign a Memorandum of
Understanding on preservation of Sundarban biodiversity.
'It will give opportunity for the government to create pressure on the
Indian counterpart to negotiate for ensuring the minimum fresh water
flow for Sundarban,' said Ainun Nishat, an expert on environment and
vice-chancellor of BRAC University.
Environmentalists said the future of Sundarban would depend on the
management of freshwater resources as much as on the conservation of
its biological resources.
http://newagebd.com/newspaper1/frontpage/32210.html
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