Mangrove wetland ecosystems in Ganges-Brahmaputra delta in ...

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442 Shafi Noor ISLAM, Albrecht GNAUCK Fig. 2(b) The limit of the Ganges delta and location of wetlands tons per day. The Ganges Brahmaputra Delta can be divided into four major categories: i) Moribund delta, ii) Mature delta and iii) Active delta and iv) Tidally active delta (Fig. 2(a)). i) The moribund delta: The western part of the deltaic plain, bound on the east by Gorai-Madhumati Rivers, comprises the areas which extend from the northern boundary of the Khulna district to Jessore and part of Kushtia district. The area of moribund delta covers an area of about 18000 km 2 . The rivers of the moribund delta cannot bring down enough water and silt, even in flood and, being confined within high levees, are not in a position to inundate the entire area. ii) The mature delta: The mature delta covers an area of about 31500 km 2 in Bangladesh and in West Bengal of India. On average, it includes Murshidabad (West Bengal, India), Nadia and 24-Parganas of India and Meherpur, Kushtia, Chuadanga, Jhenaidaha, Magura,
Mangrove wetland ecosystems in Ganges-Brahmaputra delta in Bangladesh 443 Jessore, Narial, Khulna, Sathkhira and Bagerhat districts of Bangladesh. iii) The active delta: The eastern active delta covers an area of about 16500 km 2 . This part of the Ganges- Brahmaputra delta is about 300 km long in the northsouth direction and about 100 km and 130 km wide in the upper and middle reaches, respectively. The eastern active Ganges-Brahmaputra delta includes Rajbari, Faridpur, Shariatpur, and Madaripur, Gopalgonj, Lakshmipur, Pirojpur, Barisal, Jhalokati, Patuakhali, Barguna and Bhola districts of the country. iv) The tidally active delta: The southwestern part of the Ganges delta is coastal area and a tidally active delta. It is dominated by coastal tidal currents. The tidally active delta actually is the southern part of the Sundarbans region. It covers an area of about 13500 km 2 . The Tidally active delta includes the southern part of Bagerhat, Khulna, Sathkhira district of Bangladesh and south 24 Pargona district of West Bengal in India (Islam, 2006). The surface water flow in the rivers of the Sundarbans area mainly comes from the Ganges at the off-take of Gorai-Madhumati and from the lower Meghna through Swarupkati Kocha River (Figs. 2(a) and 3). Salinity content of rivers in the Sundarbans shows a special variability. The water salinity pattern shows both seasonal and spatial variation. During pre- Fig. 3 Three ecological zones in the Sundarbans region monsoon (March–April), the conductivity of river water is high and ranges from 7 mS/cm to 52 mS/cm. In the post monsoon season (Aug-Sept), the conductivity of river water decreases (0–21.5 mS/cm). Water salinity level in the rivers of the eastern region both in pre-monsoon and post-monsoon season is low (0– 7 mS/cm) in comparison to western rivers. 5 Data and Methodology The present study was conducted based on primary and secondary data sources. The saline water and soil samples were collected and tested at the laboratory for investigation of water salinity intrusion trends. The survey covers Munchiganj, Mirgang, Koira, Kasiabad, Mongla, Kathka, Kochikhali, Hironpoint, Malancha-Mundarbaria, and Burigoalini (Fig. 3). Primary data on surface water salinity was obtained from 13 rivers including Sibsa River, Passur River, Chunnar River, Kholpetua River, Bal Jhalia River, Baleswar River, Betmargang River, Notabaki River, Passakhali River, Arpongasia River, Kathka River, Nilkamol River, and Malancha River (Fig. 4) of the Sundarbans by the Institute of Water Modelling (IWM). The survey was done in different ecologically sensitive areas between February-July in 2003.
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Mangrove wetland ecosystems in Ganges-Brahmaputra delta in ...

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