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Urban Lakes

Urban waterbodies are an inherent part of Indian culture. They served a variety of purposes. In the dry central and Southern India--that fall in the rain shadow region--they stored rainwater and ensured supply for domestic use and for agriculture. They also helped in recharging groundwater. In cities enjoying perennial river sources and high rainfall they served as flood cushions, and as in the case of Kolkata, acted as a resource recovery area, releasing nitrogen, inactivating phosphates, removing toxins and treating wastewater.

And they were taken care of by the local people, who desilted, cleaned and recharged the lakes and tanks, as a part of their regular chores. But all this changed after the government took over management of public lands in cities.

Source: Amit Kakade, CEPT, Ahmedabad
Why lakes die
Eutrophication: Industral effluents, run-off from agricultural fields, refuse and sewage are dumped into lakes. Domestic wastes like food remnants, soaps, detergents and sewage break down and release nutrients. Microscopic organisms ingest these and live off them. Following ingestion of carbonic elements, carbon dioxide is released, while some of the elements are converted into nitrates and phosphates. This is called oxidising and uses up a lot of oxygen (O2). Thus, depleted levels of dissolved O2 in water leads to a situation where other aquatic lifeforms cannot survive.

Siltation: Water flowing into a lake brings silt. Increased deforestation loosens the top soil, which finds its way into lakes. Some of the silt is washed out when the lake overflows. However, the outflow of silt does not always match the inflow and the silt settles at the bottom of the lake.

Tourism: Refuse and sewer water pour into the lake from hotels constructed on its banks. Mechanised pleasure boats create noise and leave traces of oil on the waters.

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