THE TWO major lakes in Pune — Katraj and Pashan — seem to be facing the brunt of rising pollution. The Environmental Status Report (ESR) of the Pune Municipal Corporation (PMC), which was released last week, shows a rise in both chemical and biological oxygen demands (COD and BOD), while a slight increase was seen in the dissolved oxygen (DO) levels. Measurement of the above three parametres give a fair idea about the level of pollutants in water bodies. BOD is the measure of the biological oxygen demand i.e. the oxygen necessary for aerobic microrganisms to break down organic material in water, while COD is the measure of oxygen necessary to complete chemical reactions in the water.
COD is used to quantify the amount of organic pollutants in water. Maximum permissible BOD levels for human consumption is set at 5 mg/l. Water bodies with maximum BOD levels, at 10 mg/l, are designated by the Maharashtra State Pollution Control Board (MPCB) as unfit for human consumption, or fish and wildlife propagation. DO levels should not be less than 2 mg/l for survival of aquatic life.
As per the ESR, in 2016, the BOD level in Pashan lake was 17 mg/l, while that in the upper Katraj lake was 16 mg/l. The DO levels of both the lakes was at 5.40 and 6.40 mg/l, respectively. There has been a steady increase in BOD levels in both the lakes, while DO levels have fluctuated. COD levels in Pashan lake have shown a rising trend, while that of Katraj lake had not followed any particular trend. Both Pashan and Katraj lakes have unique ecosystems and have been home to various plants and animals. Migratory birds visit the Pashan lake regularly but their numbers have been on the dip in the last few years.
PMC had carried out extensive restoration and beautification works at the site, however, discharge of sewage and other activities have harmed the lakes. As the ESR revealed, the levels of pollutants in the lakes are approaching dangerous limits. Meanwhile, Dharmaraj Patil, an environmentalist who has studied the Pashan lake, blamed the “beautification” work for the degradation of the lake. “The basic works instead of the saving the lake have destroyed the habitation of the migratory birds,” he said.
Patil also blamed the manmade dam, which allows for mixing of untreated water of Ramnadi to drain into the lake and degrade its condition. While the PMC officials conceded that the lakes were polluted, they added that the pollution levels were not alarming. “It is true that Pashan lake is getting increasingly polluted. But, this is because the water flowing for Bhugaon lake comes to Ramnadi, which is heavily urbanised. The untreated drain water flows into Ramnadi and then into the lake. Katraj lake pollution levels, however, are not very high,” added the officials.
Mangesh Dighe, who heads PMC’s environment department, said, “Both water bodies are not the sources of water supply for residents. Pollution levels in the lakes are not alarming, as is being believed. The parametres of 10 mg/l is generally applied to sewage discharged into the rivers from where water is lifted for human consumption. And these parametres do not apply to lakes, as their water is not meant for human consumption. Earlier, the parametres were 30 mg/l.”