Aquatic Pollution and Coastal Management

Unit 11 : Monitoring and control of pollution

11.4.4.West Bengal Coast
The Ganga-Brahmaputra river system transporting huge suspended load has created a vast intertidal deltaic mass ‘Sundarbans’, the largest delta in the world with an extensive mangrove forest. The Hoogly-Matla river system and other estuaries with innumerable tidal creeks and channels form an extensive network in the lower Bengal. Although the state is very rich in industrial settlement, the coastal belt is almost devoid of industries. Like the remaining coasts in the east, coastal aquaculture has been a prominent activity along the West Bengal coast. The major source of pollution is from the sewage of Kolkata metropolis and port operations at Haldia and Kolkata including growing traffic of oil tankers.
Pollution in Non-Maritime States:
The largest river in the country, the Ganga, is known to be among the most polluted rivers in the world. Sewage has been identified as the main source of pollution. In addition, the river receives considerable quantity of industrial wastes. The estimates have shown that, nearly 14,79,000 kgs of BOD is discharged into the river every day, of which, 10,90,000 kgs of BOD is contributed by Uttara Pradesh alone. The survey revealed that, nearly a 40 km stretch at Kanpur is grossly polluted, even 500% of dilution failed to improve the anaerobic condition. This condition was brought about not only by the disposal of untreated sewage, but also due to the discharge of untreated effluent from the leather and pharmaceutical industries. Further, the survey along the Varanasi sector revealed gross pollution at the vicinity of sewage and other discharge points. However, the condition gets improved after the short distance from the outfall in the further length of the river. This indicates that the river has greater dilution and rejuvenation capacity. At the confluence of Ganga and Yamuna river at Allahabad, the river water is substantially polluted due to domestic and industrial waste. According to one estimate, nearly 31.16 million tonnes of BOD and 80.40 million tonnes of suspended solids are disposed off at this stretch of the river.
The Hoogly riverine complex is formed due to the confluence of the river s Matla and Kulti. The degeneration of water quality in this riverine/estuarine complex was found mainly due to disposal of untreated sewage and pulp mill effluents. The river Hoogly receives 40,040 lb per day of BOD and 3,22,820 lb per day of suspended solids. According to one estimate, nearly 62.20% of the total BOD load in Hoogly river is from industrial waste, whereas municipal waste contributes to 37.80%. It has been observed that, pollutants have destroyed spawning ground, fish eggs and larvae and fish food organisms considerably. The pollution impact was observed on primary productivity with low rate of production and lower species diversity index of phytoplankton. As a result of this, reduction in the diversity of zooplankton and macrobenthic organisms has occurred.
About 200 million litres of raw sewage is discharged into the 24 km stretch of Yamuna in its passage through Delhi. Besides, the river receives 20 million litres of industrial waste containing half a million litres of DDT. The water quality including total bacterial load in the river Yamuna at Agra suggests that, the water quality is far from satisfactory. This riverine stretch between Delhi and Agra is grossly polluted due to the discharge of sewage and industrial wastes.
Similar kind of degradation in the river Gomati was also found to be due to factory effluents and raw domestic sewage. A recent survey of some north east rivers has indicated the presence of higher levels of iron and manganese.