Water quality management in the lower stretch of the river Ganges, east coast of India: an approach through environmental education

摘要

The lower tidal stretch of the river Ganges, known as Hugli (ca. 280 km), flows southward before entering the Bay of Bengal forming a vast mangrove-enriched estuarine delta called Sunderbans. Hugli estuary is a typical example of tide-dominated sink for contaminants from multifarious sources. This major important river is subjected to anthropogenic stress due to the socio-economic importance of these areas based on growth of industry, agriculture, aquaculture, port activities, fishing and tourism. The living resources have been degraded recently due to increases in population pressure, pollution and natural resource consumption to the extent of overexploitation. The present paper critically examines the physicochemical characteristics and level of dissolved heavy metals at three ecologically distinct zones along the course of the river — Babughat located in the eastern part of the metropolitan megacity Calcutta (140 km upstream from seaface), Diamond Harbor (70 km upstream from sea face) and Gangasagar positioned at the mouth of the Ganges estuary. Physicochemical characteristics of this partially mixed estuary are largely influenced by the interaction of seawater and discharge of riverine freshwater, annual precipitation and surface runoff. The levels of salinity, total dissolved solids, hardness and conductivity showed an increasing downward trend. Marked increase in biochemical oxygen demand (BOD) values (2.20-5.95 mg/l) was recorded in Babughat whereas correspondingly low values (0.75-2.82 mg/l) were noticed at Gangasagar. This can be attributed mainly due to huge organic load of untreated sewage from the twin city Howrah and Calcutta situated in the east and west of the river. Spatiotemporal distribution of heavy metals reveals a wide range of variations reflecting input of huge anthropogenic inputs associated with a number of physical and chemical processes. Levels of metals registered a seasonal pattern, with an increase during late monsoon months (September-October), a period characterized by low salinity and relatively low pH of the water. Elevated levels of dissolved Hg and Pb were also recorded in Babughat, with values ranging from 0.16 to 0.95 μg/ml and 0.017 to 0.076 μg/ml, respectively, this high values for Hg can be attributed to the discharge from pulp and paper manufacturing units and to atmospheric input and runoff of automobile emission for Pb. It was revealed that the socio-economic development of Calcutta, the most potential economic zone in India situated on the east bank of Hugli river, has had a significant impact on the water quality of this major river. The deterioration of water quality is directly related to non-functioning and malfunctioning of wastewater treatment plants and lack of environmental planning and coordination. To restore the ecological stability and economic vitality of this river, the following measures have been suggested: (ⅰ) strong vigilance programme is to be undertaken towards installation and maintenance of the wastewater treatment plants to check the flow of persistent contaminants in the river water and (ⅱ) execution of legislation and mass awareness programmes are to be enacted to restore the sound health of the river. The authors urge that environmental education should be used as an effective tool for water resource management dealing with intricate and complex problems in the interaction between nature, technology and human beings.