Wetlands comprise around 6.4 per cent of the earth’s surface and are found across different climatic zones. Many major urban centres are located near water based ecosystems—coastal, riverine or riparian. Hence wetlands are most critically threatened by the rapid expansion of cities. Cities are not self-sustaining; they are systems dependent on the natural environment. Vegetated tracts, urban wetlands, water bodies and riverine systems are crucial for the city. The productive capacities of wetlands cannot be determined by price or market value; yet, they facilitate by their existence itself. Unfortunately, this trade-off has often been neglected in urban planning. Consequently, the destruction and pervasive neglect of urban wetlands has taken a severe toll on our very existence.
The major functions and significance of urban wetlands are often unrealised. Michael Williams (1991) categorically listed the functions of wetlands. Some are of particular significance to urban areas:
Natural flood mitigation: Wetlands temporarily absorb or contain run-off water and thereby protect downstream areas from being inundated. Instead of building expensive dams, or dredging, retention of urban wetlands may be the most cost-effective flood management.
Recharging of aquifers: An aquifer is a zone surrounded by impervious rock layers and effectively holds ground water much better than structures overlaid and underlain by porous rock strata. Water infiltrates from the surface and recharges the water table, with the aquifers retaining it and serving as a source of precious groundwater all year round. The presence of wetlands protects and recharges groundwater aquifers. Draining them reduces the stock of groundwater, with the added danger of saline water contaminating fresh water aquifers. This can be critical to cities with high population densities.
Sediment trapping: By reducing the velocity of flowing water, urban wetlands protect channels from erosion. Deposition rates are understood to range from 2-45 mm per year, depending on the slope of land and sediment type. The entrapment process is further improved due to vegetation. While sediments may harm water quality, they also absorb nutrients, pesticides, heavy metals and hydrocarbons that could otherwise seep into the soil.
Atmospheric and climatic fluctuations: There is evidence to prove that urban wetlands may have a role in global biogeochemical fluxes. Armentano and Menges (1986) conclude from studies that temperate organic wetlands act as net carbon sink and absorb between 57 x 106 and 83 x 106 tonnes of carbon per year.
Trapping and removal of waste: Wetlands have the capability to process human and animal waste material in an efficient way, which implies that their prolific growth removed pollutants from the water and substrate. Several case studies support this conclusion. Boto and Patrick (1979) study on the Manitowoc River in Wisconsin, found that the marshes effectively remove an average, 86.2 per cent of coliform bacteria from faeces, 80.1 per cent of the biological oxygen demand, 43.7 percent of the chemical oxygen demand, 29.1 per cent of suspended solids and 13.4 per cent of total phosphorus. Besides, turbidity is reduced by 43.5 per cent.
Productivity: Wetlands comprise 6.4 per cent of the earth’s surface while contributing to 24 per cent in primary productivity, and compare nearly on par with rainforests. According to Leith (1975), the net primary productivity range of wetlands is 800–4000 gms/sq.m/yr, as compared to rainforests, which boast a productivity range of 1000–3500 g/sq.m/yr.
Fish and Wildlife Habitat: The most widely known function of wetlands that has been studied in great detail, although at a much localised level, is their role as a habitat for a wide range of flora and fauna, including fish and wildlife.
Livelihood Sustenance: Wetlands are an important livelihood base for agriculture and fishing. Many water-based species of flora and fauna are found in wetland areas. Kolkata, for instance, gets around 55000 tonnes of fresh vegetables and 75000 tonnes of fish annually from its eastern wetlands (Ghosh & Sen, 1997). The most important consumptive values are derived by water itself, which is used for a variety of domestic, manufacturing and construction purposes.
Urban Wetlands in India
Most Indian cities have developed around water bodies, wetlands and riverine ecosystems, and hence encounter the challenges of degradation and active conversion for infrastructure and real estate development. Wetlands in India account for approximately 7.4 per cent of the total geographical area. India is one of the first signatories to the 1971 Ramsar Convention on wetlands. Population pressures and demand for land has resulted in rapid conversion of water bodies and wetlands in the recent past.
Notwithstanding the mandates and legislations on environment, the interventions by the government, planners or civil society in actively protecting wetlands from conversion is not enough.
By a rough estimate, around 38 per cent of India’s wetlands have been lost in a decade (Vijayan et al., 2004). In cities, losses have amounted to 80-95 per cent in some cases. According to a Report (CSE, 2013) Hyderabad has lost 3245 hectares (ha) of wetlands, 65 out of 137 lakes in Ahmedabad were built over, and 21 out of 44 water bodies in Delhi went dry in a decade. The Pallikaranai marshland in Chennai has also been reduced to 12 per cent of its original 5000 ha (Panda, 2016, January 24). In Mumbai, the Powai and Vihar lakes are threatened by pollution and degradation due to construction activity. Cuttack has lost half its water bodies in just two decades. In four decades, 54 per cent of the lakes in Bangalore have been illegally encroached upon, while more than 100 wetlands have been lost, implying a 99.8 per cent loss (Kiran & Ramachandran, 1999). The Salim Ali Centre has identified 700 wetlands in India, of which around 200 are in peril. Incidentally, only 26 wetlands in India have been incorporated in the Ramsar List upto 2015. Even so, they remain ineffectively governed, and continue being vulnerable to encroachment, planned development, pollution, eutrophication, unplanned tourism, besides religious and cultural factors.
East Kolkata Wetlands
Kolkata is located on the Hugli-Bhagirathi, a distributary of the Ganga. An extensive tract of around 12500 ha of wetlands and water bodies is located to the east of the city; these wetlands have always been the city’s natural drainage spill basin.
The urban sprawl is gradually having its impact upon these extensive wetland tracts, which includes an interconnected system of distributary streams, canals, natural water bodies as well as manmade fisheries. The management of urban wastewater in most developing countries is a difficult problem as the installation of a mechanical plant to tackle the growing urban population is too expensive. But when the urban wastewater of Kolkata was diverted into the wetlands through some canals and underground conduits during the first half of the 19th Century, an indigenous system of waste recycling and resource recovery emerged thereon. It was also a livelihood compulsion for communities living adjacent to these wetlands to convert this wastewater into a resource. The development of a system of sewage-fed-fisheries has been a boon to Kolkata. In fact only 3500 ha are assigned to wetlands, while the remaining area functions as a waste recycling zone.
Apart from this, its location upon the ‘fringes of the active delta, hardly a few feet above sea level’ and its location ‘along the track of tropical cyclones coming up from the Bay of Bengal’ (Munshi, 1991) gives it a unique environmental characteristic, not found in any other populous metropolis in the world. Located in close proximity to the Sunderban, where some 5,366 sq km (about 56 per cent) of tidal wetlands have been converted for paddy cultivation (Bandyopadhyay, 1997) the intricately linked eastern wetlands remain extremely vulnerable to urbanisation.
As compared to recurring costs for a 45 mld waste treatment plant amounting to INR 1.1 crore, the east Kolkata wetlands serve as a waste recycling zone for the city’s sewage at no cost at all (Bandyopadhyay, 2004).
However, rapid land use changes towards the east of the Salt Lake township, especially with the 2750 hectares urban complex of Rajarhat-New Town, have diminished and endangered these unique wetlands. Hydrologists opine that these land use changes may end up increasing flooding events, primarily due to run-off being intercepted. Kolkata’s eastward growth spells disaster for the east Kolkata wetlands, as also the city in general. However, unfortunately this direction has already been chosen for development of ultra-modern infrastructure, housing and commerce.
Figure 1 highlights a small wetland area in east Kolkata that has shown marked landuse change over a decade.
Notwithstanding the ecological functions that they play, wetlands tend to be viewed as sites that could be easily converted to other competitive uses. This gets facilitated by the fact that its ‘valuation’ is unknown and is treated as a free good. Urban growth, infrastructural developments, pollution and eutrophication have endangered a multitude of lakes and wetlands all over India. Their disappearance will spell the death of a balanced ecosystem, putting nature, lives and livelihoods at risk. Promoting urban development by building around wetlands, instead of annihilating them, seems the only solution.
Armentano, T.V., & Menges, E.S. (1990). Patterns of change in the carbon balance of organic soil wetlands of the temperate zone. Journal of Ecology, 74, pp755-774.
Bandyopadhyay, S. (1997). Natural environmental hazards and their management: a case study of Sagar Island, India. Singapore Journal of Tropical Geography, 18(1), pp20-45.
Bandyopadhyay, S. (2004). Social perceptions of urban wetlands in Kolkata (unpublished doctoral thesis). Department of Humanities and Social Sciences, Indian Institute of Technology, Bombay.
Boto, K.G., & Patrick, W.H. (1979). Role of wetlands in the removal of suspended sediments. In P.E. Greeson, J.R. Clarke & J.B. Clarke (Eds.), Wetland functions & values: the state of our understanding. Minneapolis: Water Resources Association Technical Publication. pp479-88.
Centre for Science and Environment. (2013). Protection and management of urban lakes in India. New Delhi.
Ghosh, D. & Sen, S. (1997). Ecological history of Calcutta’s wetland conversion, Environmental Conservation, 14(3), pp219-226.
Kumar, R. (2008). Urban development, biodiversity and wetland management case study: East Kolkata wetlands, India. Wetlands International. Retrieved from http://ramsar.rgis.ch/pdf/KUMAR_UNHABITAT_East_Kolkata_Wetlands_PDF.pdf.
Kiran, R. & Ramachandran T.V. (1999). Status of wetlands in Bangalore and its conservation aspects. ENVIS Journal of Human Settlements, pp16-24.
Leith, H. (1975). Primary productivity of the major vegetation units of the world. In H. Leith & R.H. Whittekar (Eds.), Primary Productivity of the Biosphere. Berlin: Springer-Verlag.
Michael, W. (1991). Wetlands: a threatened landscape. London: Blackwell Publishers.
Munshi, S.K. (1991). Calcutta: land, land use and land market. In B. Dasgupta (Ed.), Calcutta’s urban future. Govt. of West Bengal.
Panda, R. (2016). Five flood prone Indian cities and their lost water bodies. The Big Wire. Retrieved from http://bigwire.in/2016/01/24/five-flood-prone-indian-cities-and-their-lost-water-bodies/
Vijayan, V.S., Prasad, S.N., Vijayan, L., & Muralidharan, S. (2004). Inland wetlands of India: conservation priorities. Combaitore: Salim Ali Centre for Ornithology and Natural History.