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Bangladesh Sundarbans: Present Status of the Environment and Biota

Abdul Aziz
Department of Botany, University of Dhaka, Dhaka 1000, Bangladesh

Ashit Ranjan Paul
Assistant Chief Conservator of Forests
Bangladesh Forest Department, Ban Bhaban, Agargaon, Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

The Sundarbans is a deltaic mangrove forest, formed about 7000 years ago by the deposition of sediments from the foothills of the Himalayas through the Ganges river system, and is situated southwest of Bangladesh and south of West Bengal, India. However, for the last 40 years, the discharge of sediment-laden freshwater into the Bay of Bengal through the Bangladesh part of the Sundarbans Mangrove Forests (BSMF) has been reduced due to a withdrawal of water during the dry period from the Farakka Barrage in India. The result is two extremes of freshwater discharge at Gorai, the feeding River of the BSMF: a mean minimum monthly discharge varies from 0.00 to 170 m³·s⁻¹ during the dry period with a mean maximum of about 4000 to 8880 m³·s⁻¹ during the wet period. In the BSMF, about 180 km downstream, an additional low discharge results in the creation of a polyhaline environment (a minimum of 194.4 m³·s⁻¹ freshwater discharge is needed to maintain an oligohaline condition) during the dry period. The Ganges water carries 262 million ton sediments/year and only 7% is diverted in to southern distributaries. The low discharge retards sediment deposition in the forestlands’ base as well as the formation of forest lands. The increase in water flow during monsoon on some occasions results in erosion of the fragile forest lands. Landsat Satellite data from the 1970s to 2000s revealed a non-significant decrease in the forest lands of total Sundarbans by 1.1% which for the 6017 km² BSMF is equivalent to 66 km². In another report from around the same time, the estimated total forestland loss was approximately 127 km². The Sundarbans has had great influence on local freshwater environments, facilitating profuse growth of Heritiera fomes (sundri), the tallest (at over 15 m) and most commercially important plant, but now has more polyhaline areas threatening the sundri, affecting growth and distribution of other mangroves and biota. Landsat images and GIS data from 1989 to 2010 at the extreme northern part of Khulna and Chandpai Ranges revealed the formation of a large number of small rivers and creeks some time before 2000 that reduce the 443 km² forestland by 3.61%, approximately 16 km², and decreasing H. fomes by 28.75% and total tree cover by over 3.0%. The number of the relatively low-priced plants Bruguiera sexangula, Excoecaria agallocha and Sonneratia apetala, has, on the other hand, increased. Similar degradation could be occurring in other ranges, thereby putting the survivability of the Bangladesh Sundarbans at risk. The growing stock of 296 plants per ha in 1959 had been reduced to 144 by 1996. Trend analysis using “Table Curve 2D Programme,” reveals a decreased number of 109 plants by the year 2020. The degradation of the Bangladesh Sundarbans has been attributed to reduced sediment-laden freshwater discharge through the BSMF river system since commissioning the Farakka Barrage on 21 April 1975 in India. To reduce salinity and forestland erosion, the maintenance of sediment-laden freshwater discharge through its river system has been suggested to re-create its pre-1975 environment for the growth of H. fomes, a true mangrove and the highest carbon-storing plant of the Sundarbans. This may possibly be achieved by proper sharing of the Ganges water from the Farakka Barrage, forming a consortium of India, Nepal, Bhutan and China, and converting parts or whole of the Ganges River into water reservoir(s). The idea is to implement the Ganges Barrage project about 33 km downstream, dredging sediments of the entire Gorai River and distributaries in the Ganges floodplain, thus allowing uniform sediment-laden freshwater flow to maintain an oligohaline environment for the healthy growth of mangroves. The system will also create healthy hinterlands of the Ganges floodplain with increased crop production and revenue. The expenditure may be met through carbon trading, as Bangladesh is a signatory of the Copenhagen Accord, UN Framework Convention on Climate Change. The total carbon reserve in the BSMF in 2010 was measured at about 56 million metric tons, valued at a minimum of US$ 280 million per year. The forest is rich in biodiversity, where over 65 species of mangroves and about 1136 wildlife species occur. The BSMF acts as a natural wall, saving property as well as millions of lives from natural disasters, the value of which is between 273 and 714 million US$. A 15 to 20 km band impact zone exists to the north and east of the BSMF, with a human settlement of about 3.5 million that is partly dependent on the forests. Three wildlife sanctuaries are to the south of the BSMF, the home of the great royal Bengal tigers, covering a total area of about 1397 km². Construction of a coal-fired power plant at Rampal will be the largest threat to the Sundarbans. It is a reserve forest, declared as a Ramsar site of international importance and a UNESCO natural world heritage site.

Keywords: The Sundarbans; mangroves; Sundari; forests; salinity; Ganges River; Farakka Barrage

Location: Sundarbans, Bangladesh

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Plant, Sundari

Objectives:

The review of the Bangladesh Sundarbans is aimed at understanding the causes of degradation of the environment and the biota, and developing a possible method towards its reclamation as a healthy forest land environment and the growth of Heritiera fomes (sundri), a mangrove species truly representative of this forest type.

Methodology:

This paper is intended as a review rather than as a research paper. The majority of the paper is based on analysis of existing literature and critiques of adaptation planning and mainstreaming in Bangladesh since the publication of the review, and supports this analysis with Wildlife Trust of Bangladesh (WTB), World Conservation Monitoring Centre, Forest Department, Ministry of Environment and Forests, etc., conducted with Government, non-governmental organization (NGO) and donor officials engaged in the processes described.

Source of Information: Diversity, 2015, 7, 242-269, ISSN 1424-2818

Article Link (Online Journal): http://www.mdpi.com/1424-2818/7/3/242/pdf

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The Sundarbans is a deltaic mangrove forest having freshwater influence, formed about 7000 years ago by the deposition of sediments from the foothills of the Himalayas through the Ganges river system. However, the discharge of sediment-laden freshwater into the Bay of Bengal through the Bangladesh part of the Sundarbans Mangrove Forests (BSMF) has been reduced due to a diversion of water during the dry period from the Farakka Barrage in India since 1975. The BSMF receives a mean minimum monthly discharge of 0.00 to 170 m³·s⁻¹ during the dry period when a minimum of 194.4 m³·s⁻¹ freshwater discharge is needed to maintain a low saline condition inside the forests. The zero or very low discharge through the forests allows seawater intrusion deep inside the BSMF increasing salinity of water and soil. This affects the growth of Heritiera fomes (sundri), the tallest (at over 15 m) and most commercially important plant and also affecting growth and distribution of other mangroves and biota. The high salinity results increase in relatively low-priced plants Bruguiera sexangula, Excoecaria agallocha and Sonneratia apetala. The growing stock of 296 plants per ha in 1959 had been reduced to 144 by 1996. Trend analysis using “Table Curve 2D Programme,” reveals a decreased number of 109 plants by the year 2020. The Ganges water carries 262 million ton sediments/year and only 7% is diverted in to southern distributaries recorded in 2007. The low discharge caused deposition of sediments in the Ganges and Gorai Rivers forming huge sandbars that retarded uniform sediment deposition in the forestlands’ base as well as the formation of new forestlands for 40 years in the BSMF. The situation has weakened the existing forestlands thereby putting the survivability of the Bangladesh Sundarbans at risk. The sediment laden freshwater discharge in the wet season (July to October) is high with a mean maximum of about 4000 to 8880 m³·s⁻¹. The huge discharge in association with the cyclone on some occasions, result in the erosion of the fragile forestlands and formation of a large number of small rivers and creeks increasing the marsh and water areas. Landsat Satellite data of the last nearly four decades revealed an estimated loss of 66 to 127 km² forestlands. The total carbon reserve in the BSMF in 2010 was measured at about 56 million metric tons, valued at a minimum of US$ 280 million per year. The BSMF acts as a natural wall, saving property as well as millions of lives from natural disasters. The value of the ecosystem services is between 273 and 714 million US$ per year. The degradation of the Bangladesh Sundarbans has been attributed to reduced sediment-laden freshwater discharge and increased salinity since commissioning the Farakka Barrage in India. To reclaim the Bangladesh Sundarbans the maintenance of sediment-laden freshwater discharge through its river system has been suggested to re-create its pre-1975 forest environment for the growth of H. fomes. This may possibly be achieved by proper sharing of the Ganges water from the Farakka Barrage during dry period, forming a consortium of India, Nepal, Bhutan and China, and converting parts or whole of the Ganges River into water reservoir(s). The idea is to implement the Ganges Barrage project about 33 km downstream, dredging sediments of the entire Gorai River and distributaries in the Ganges floodplain, thus allowing uniform sediment-laden freshwater flow to maintain a low saline environment inside the BSMF and deposition of sediments around forest lands. The system will also create healthy hinterlands of the Ganges floodplain with increased crop production and revenue. The expenditure may be met through carbon trading, as Bangladesh is a signatory of the Copenhagen Accord, UN Framework Convention on Climate Change. Construction of a coal-fired power plant at Rampal only 14 km away will be the largest threat to the Bangladesh Sundarbans.

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