Covering an area of 12,500 hectare, the East Kolkata Wetlands includes about 254 sewage-fed fisheries, agricultural land, garbage farming fields and some built-up area. As much as 45.93% of the area is manmade.
Kolkata: If you happen to live in Kolkata or have visited it, you may have either seen or heard about the large waterbodies alongside the Eastern Metropolitan Bypass, towards Salt Lake and in New Town. However, did you know that these waterbodies and the adjoining sewage farms — known as the East Kolkata Wetlands — maintain the ecological balance in the fast-expanding metropolis?
What are this East Kolkata Wetlands?
The East Kolkata Wetlands or the EKW is a unique example of innovative resource reuse system through productive services. Covering an area of 12,500 hectare, it includes about 254 sewage-fed fisheries, agricultural land, garbage farming fields and some built-up area. As much as 45.93% of the area is manmade.
Developed by the local people through ages, the resource recovery system using the wastewater from the city is the largest in the world and unique among its types. Being a buffer zone in the ancient times, the EKW had been a dumping ground of both solid garbage and sewage until the recent past. However, the practice of sewage-fed pisciculture and agriculture has turned this dumping ground into a natural waste recycling region.
In August 2002, the East Kolkata Wetland Area was included in the list maintained by the Ramsar Bureau as a wetland of International Importance.
Where are the East Kolkata Wetlands located?
The East Kolkata Wetlands is located in the eastern outskirts of Kolkata. It stretches over two districts — North 24 Parganas and South 24 Parganas. According to records, the climate here is subtropical with an annual mean rainfall of about 200 cm.
Biodiversity in East Kolkata Wetlands
The area is rich in bio-diversity as it contains about 104 plant species, 20 important mammalian species, various threatened species, 40 bird species including both local and migratory, 52 endemic varieties of fishes out of which 34 are threatened. The existence of bacteria, archaea, fungi, algae, protozoa and protists make microbial diversity an integral part of bio-diversity. Soil samples show existence of not only ecologically important microbes but also some that are important commercially.
Waste is recycled here using the principal resource recovery practices including garbage vegetable farms, fishponds holding wastewater, fishpond effluents used for paddy fields and aquaculture with sewage for brackish water.
Shallow flat bottom ponds with wastewater are locally called bheris. Having a depth and size of about 50 cm to 150 cm and 40 ha to 50 ha, respectively, the bio-remedial activities is mainly due to the high rate of photosynthesis in the basin. The factors that play an important role in the purification process are the shallowness of the pond, abundance of water hyacinth helping in the accumulation of metals, sunlight reaching the bottom of the pond and last but not the least, the wind.
According to a study, the fishes thriving in the wetland maintain the population of planktons in a proper balance and also at the same time, convert the available pond nutrients into an edible form (fish) thus making them play a huge ecological role. The pond algae play a major role in removing faecal bacteria. Phyto-remediation is the process by which the green plants such as aquatic weeds remove, contain or convert the environmental contaminants. The roots of the water hyacinth act as a biological filter and absorb heavy metals present in the wastewater.
Other environmental and economical importance
Apart from its contribution in waste management – the EKW act as a carbon sink and clean up the city’s air, maintain the micro climatic condition of the region and pass flood waters during the monsoon. East Kolkata Wetlands fulfill the requirement of fish, vegetables and food grains in the city and at the same time, provide livelihood to thousands of local villagers who have the unique skill to use wastewater to grow fish and vegetables.
Challenges faced by EKW
The EKW is facing major threats against its existence. Illegal land conversion and building construction are reducing its area. There is also a conflict of interest among the fishermen over the allocation of sewage. The ecological, environmental and economical importance of East Kolkata Wetlands demands proper conservation and management measures some of which have already been initiated by the state government.