The East Kolkata Wetland System
The wetlands to the east of Kolkata (22 0 27’ N 88 0 27’ E) comprises a large number of water bodies distributed across the districts of South and North 24 Parganas. The multifunctional wetland ecosystem is spread over 12,500 hectares. It has, along with the wetlands, 254 sewage-fed fisheries, agricultural and solid waste farms and some built up areas. The resource recovery system developed by the local people over many years using waste water from the city is the largest and the only one of its kind in the world. It also helps in water treatment, and is home to waterfowl and a large biodiversity.
In August 2002, 12,500 hectares of the East Kolkata Wetland area was included in the ‘Ramsar List’ making it a ‘wetland of International Importance’. (The Ramsar Bureau List was established under Article 8 of the Ramsar Convention.)
The hydrology of this wetland is different from any other aquatic systems. The wetland has no catchment of its own, though approximately 250 million gallons of sewage flows into it every day. There are hardly any aquifers even up to a depth of 400 feet. Water can be found only in perched aquifers.
The total dissolved solid content sometimes exceeds 1800 ppm. The water table is approximately at a depth of 8 metres which falls by 1 - 2 metres during summer. The average pH in the fish ponds is 7.5. The BOD (a measure of the organic pollution) in the fisheries is between 35 and 50 ppm and the COD between 55 and 140 ppm.
The waste recycling system
The Kolkata Municipal Corporation area generates roughly 600 million litres of sewage and wastewater everyday and more than 2,500 metric tons of garbage. The wastewater flows through underground sewers to pumping stations in the eastern fringe of the city, and is then pumped into open channels. Thereafter, the sewage and wastewater is drawn into the fisheries of the East Kolkata Wetland by the owners of the fisheries. Here, after a few days, the organic compounds of the sewage and wastewater biodegrade.
The organic loading rate in these fish ponds appears to vary between 20 - 70 kg a hectare a day (in the form of bio-chemical oxygen demand). A network of channels is used to supply untreated sewage and to drain out the spent water (effluent). The cumulative efficiency of reducing the BOD of the sewage wastewater is above 80% and for coliform bacteria 99.99% on an average. The solar radiation is about 250 langleys a day, and is adequate for photosynthesis. In fact, the sewage fed fishery ponds act as solar reactors. Solar energy is tapped by a dense population of plankton. Plankton are consumed by the fish. Though the plankton play a significant role in degrading the organic matter, its overgrowth becomes a problem for pond management. It is at this critical phase of the ecological process that the fish play an important role by grazing on the plankton. The two fold role played by the fishes is indeed crucial–they maintain a proper balance of the plankton population in the pond and also convert the available nutrients in the wastewater into readily consumable form (fish) for humans. The fish farmers of East Kolkata Wetlands have developed such a mastery of these resource recovery activities that they are easily growing fish at a yield rate and production cost unmatched by any other fresh water fish ponds of this country.
What the wetlands offer Fish:
The city of Kolkata gets its huge volumes of daily sewage treated at no expense and gets in addition a substantial daily supply of highly edible freshwater fish (a very essential protein supplement in their daily food). In fact, Kolkata city receives about one third of its daily requirement of fish from the sewage-fed fisheries (about 11,000 metric tonnes annually).
Kolkata generates roughly 2,500 metric tons of garbage (solid waste) a day which is collected and dumped at designated sites in the wetlands. The garbage filled areas are extensively used to raise a variety of vegetables. The city receives roughly 150 metric tons of vegetable everyday from its garbage farms.
The paddy fields in the wetlands (many of which are irrigated by the effluent water of the fisheries) produce 15,000 metric tons of paddy annually.
It is claimed by environmentalists that these wastewater bodies and fisheries act as a carbon-dioxide sink and help to improve the quality of air of Kolkata and its environment. Any loss of the wetlands, therefore, will have a negative impact on the overall environmental condition of the area. So, the role and importance of the wetland in relation to its surroundings cannot be undermined.
The East Kolkata Wetlands and waste recycling region serve to:
a) absorb and treat in the most efficient, economical and natural way the huge volume of sewage and wastewater and urban solid and air wastes generated by Kolkata at no cost to the city.
(b) fulfill substantially the requirement of fish, vegetables and food-grains in the city.
(c) absorb the pollution from, and purify the air that citizens breathe.
(d) absorb and pass to downstream creeks and the sea the flood waters that the monsoon brings to the city.
(e) provide a habitat for a variety of flora and fauna and living organisms endemic to wetlands.
(f) provide the food chain and waste-to-wealth recycling so unique and essential to this city.
(g) maintain the micro-climatic condition of the region.
(h) maintain the delicate ecological balance in a fragile environment and eco-system.
(i) provide livelihood support for thousands of local villagers who also have the unique skill of using wastewater to grow fish and vegetable and thereby help sustain a stable urban fringe.
Centre For Environmental Management And Participatory Development (CEMPD),
an NGO engaged for conducting several stake holder consultation with villegers, schools and local clubs in the EKW area to generate awareness regarding EKW and about its Ramsar status. Moreover, livelihood practices which maintain ecological balance in the area, are also being mapped.
Period of Engagement:
1st March 2006
31st August 2006
Present land use pattern
Satellite pictures and ground surveys show that: