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Biological Aspects of the Coastal and Marine Environment of Bangladesh

Md.Shahadat Hossain
Integrated Tropical Coastal Zone Management, Asian Institute of Technology, Mail Box No. 866, Pathumthani 12120, Thailand

Abstract/ Executive Summary:

Bangladesh, which has a warm tropical climate and abundant annual rainfall, has very rich coastal waters; these support diverse and abundant marine life.The coastal and marine environment is becoming increasingly important in fulfilling social, economic, development and strategic objectives of the country.The biological character is briefly reviewed to provide a background to the main habitats and their condition.The marine resources are described, while emphasis is given to living resources, particularly ecosystems and fisheries.Of the intertidal ecosystems, mangroves are the most diverse and highly productive and very important regionally.Considering the major regional and global context, fisheries and aquaculture are important, particularly for penaeid shrimp (Penaeus monodon) and also for pomfret, hilsa shed, bombay duck, mackerel, eel, ribbon fish, snapper, cat fish and Indian salmon.Oil, domestic, urban and industrial pollutants are a problem in several parts of the coastal zone, although effects on ecosystem structure and function are generally not well known.The coastal zone is also fast becoming the depository for solid wastes.The orientation towards coastal management action requires clear guidance, a well-organized government structure, and } most importantly } a well defined set of objectives and actions. # 2001 Elsevier Science Ltd.All rights reserved.

Keywords: Biological aspects, Coastal, Marine environment, Bangladesh

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Program Area: Risk Management in Agriculture

Commodity: Pollution

Objectives:

The vulnerable coastal zone suffers at present from water pollution, which has become a serious problem all over the world and is getting aggravated in the developing countries.This is particularly significant for Bangladesh because the large number of rivers and waterways which criss-cross the entire country, and which also drain water from the upstream countries (India, Nepal, Bhutan and China) and finally empty into the Bay of Bengal, play a vital role in carrying pollutants from different sources.Due to circulation pattern of the Bay, polluted waters are compounding the coastal as well as international water quality problems.

Methodology:

Hydrometeorology The coastal zone of Bangladesh enjoys a tropical maritime climate, which is more or less similar to that country’s climate.The entire coastal zone is prone to violent storms and tropical cyclones during pre-monsoon and post-monsoon seasons.Sometimes cyclones associated with tidal waves cause great loss of lives and property. 2.1. Winds The effects of local winds appear to be more important to the marine biota, especially in terms of existing stress, than the broad scale wind systems.Along the coast in summer, strong winds build up in the afternoons from ‘sea breeze’ effects, where the hot land heats overlying air, which rises due to convection, bringing surface flows.Land breezes can occur at night and, although less frequent, have powerful desiccating effects, especially on the intertidal biota and coastal vegetation. During summer (April–October) the southwest monsoon wind blows persistently, creating clockwise circulation.At this time the northern Indian Ocean wind system coupled with the Himalayas Mountains, thus creates the world’s highest rainfall.The rainwater drains into the Bay and decreases salinity.During winter (November– March) the northeast monsoon wind blows and the surface water forms an anticlockwise circulation.In particular, the monsoon is a cold northwesterly wind that flows down from the mountains of the Himalayas, bringing a severe chilling.The monsoons are not unusual, and more or less severe versions occur each year. 2.2. Rainfall Mean annual rainfall in the southeastern part (Cox’s Bazar) is 3558 and 1638 mm in the southwest part (Satkhira).About 80–90% of annual rainfall is confined to the monsoon months (April–October). 2.3. Air temperature In the coastal zone of Bangladesh maximum air temperature is attained during March–April, which ranges from 31.18C to 33.38C.During November–December temperatures fall gradually within a range between 218C and 298C. 2.4. Salinity The principal feature of the coastal water hydrology is the presence of a prolonged low saline regime mostly during the monsoon and post-monsoon seasons due to heavy precipitation.Evaporation is high in winter as well as summer, maintaining raised salinity in the coastal water.Winds throughout the year maintain strong evaporation and severely elevated salinity in the southern coast (characterized by Cox’s Bazar and around Saint Martin’s island) and in summer very high temperature may increase this further.The surface salinity distribution varies from 10 to 29 ppt and the salinity increases rapidly with depth in the upper 20–30 m. 2.5. Dissolved oxygen The oxygen content decreases rapidly with depth within the upper part of the thermocline.The isoline for 1 ml/l is reached at about 80 m in May and 100 m in November–December. There seems to be a minimum in the vertical oxygen distribution between 200 and 400 m. 2.6. Water temperature Surface water temperature varies in different months from 22.88C to 32.98C.The vertical temperature distribution showed a subsurface maximum at about 10–30 m depth due to cooling of the surface layer and the depth of the thermocline varies from 30 to 70 m depth. 2.7. pH pH ranges between 6.9 and 8.9. The lowest value has been recorded in September and the highest in January. 2.8. Tide Tidal streams are important local mechanisms of water, nutrient and pollutant movement.They are also the reason why rich marine biota exists in coastal water. Important also is tidal turbulence over the seabed, which mixes the water column vertically.Tides are semi-diurnal, showing two high and two low waters during a lunar day.Tidal behaviour varies along the coast in terms of magnitude but not of pattern.The variation in such a short coastline might be attributed to the shallowness of the Bay and varying topography of coastal waters.The tidal range at the head of the Bay of Bengal is strong, ranging from 1.3 m at neap tide to about 4.83 m at spring tide near Sagardip. Similarly, 4.27 m neap tides and 6.10 m spring tides are observed in the Sandwip area (Satalkhal).This range is reduced toward the south along the eastern shore of the Bay of Bengal. At Sadarghat, Chittagong, monthly mean tidal range varies from 1.48 to 4.90 m with a 24 year average of 3.84 m. The topography of the coastal zone and the tidal patterns of the Bay of Bengal play an important role in the economy of the area.During the lean period (April and May), the tide penetrates up to 170 km in the north (Khulna–Satkhira area) and to 340 km in the northeast region (Sylhet area).Along the east coast, the tide penetrates only from zero to 50 km depending on the topography and presence of channels in the area. 2.9. Current The main, broad-scale circulation in the marine water of Bangladesh is clockwise and anti-clockwise rotation, which is created by the wind.Velocity of current varies from 4.5 to 5.5 knots during spring tide in the summer monsoon while in the neap tide it is 2.3 to 3.9 knots. 2.10. Wave Waves running up the coast often throw large numbers of organisms on to the beach, where they die.Wave height in the marine water of Bangladesh varies from 20 to 30 ft.

Source of Information: Ocean & Coastal Management 44 (2001) 261–282

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Achievement/Findings:

Environmental education is directly relevant to improved natural resources management and there is an urgent need for awareness development programmes. As the poor living in and around the wetlands are the key actors in conservation, it is imperative to seek their cooperation and involvement in the programmes of critical local significance.The curricula of primary and secondary schools in which some components of natural resources conservation are already included, should be further strengthened by demonstration projects, field training and voluntary services supported by video films and graphics.The news media can play an important role in disseminating information on functions and values of coastal and marine environment.As women play a crucial role in the conservation of the environment, action programmes with social participation by women should be encouraged.The potential role of religious institutions in developing environmental ethics should be explored.As the livelihood of the people is closely knit with the environment, they should be made aware of the impacts of development programmes before implementing them. Land use zoning can be done on the basis of suitable criteria for different activities or mixes of activities for sustainable resource utilization, their conservation and conflict reduction.This can maximize productivity through optimal allocation of resources to different kinds of development activity and minimize the conflict between different users, which improve the socio-economic condition of the people as well as maintain the ecological balance in the coastal region. On the other hand, continuous environmental monitoring, surveillance and vigilance in the coastal and sea areas should be undertaken with the participation and views of the local community.Environmental Impact Assessment (EIA) must be completed before projects are approved regarding water and coastal resource management, industries, energy development and communication.Government intervention may be needed in granting of additional incentives for using antipollution technologies and facilities.In certain cases subsidy is needed to construct common waste treatment facilities.Establishment of a strong green belt along the coast through proper afforestation is essential.Sewage treatment plants should be installed immediately in major cities/towns and introducing cheaper local technology must develop rural sanitation systems.

Knowledge Management: Journal