PANAJI: Duckweed infestation due to high concentration of nutrients flowing in from St Inez creek and resultant pollution is suffocating aquatic life in Miramar lake and causing environmental problems for nearby residents.
Chemical and biological analysis of samples drawn from the bottom and surface of the water body by National Institute of Oceanography (NIO) scientists for a study at the request of corporation of the city of Panaji (CCP) has shown very high levels of pathogenic bacteria like E coli and also high concentrations of trace metals such as iron, mercury and copper in it.
The lake with an area of approximately 10,000sq m and an average depth of 1.6m is linked on the south-eastern side to the highly polluted St Inez creek.
Local residents had not noticed such thick growth of the weed in the past. “After the heavy rainfall due to a cyclone in October, the weed appears to have entered from the fields in Camrabhat,” Surendra Furtado, mayor of the corporation of the city of Panaji (CCP) said.
The NIO study has shown a high level of pollution in the water body. “The lake has lost oxygen below the surface due to eutrophication and resultant decay of algae in the bottom layer. These anoxic conditions are not conducive for higher life forms and only anoxic bacteria can survive in such systems,” S W A Naqvi, NIO director said.
The obnoxious gases emanating from the water body are causing a problem to nearby residents.
NIO has suggested a few measures to rid the lake of high concentrations of nutrients. “In order to maintain a healthy environment in the lake, nutrient concentrations in the source water should be controlled,” the study states.
The process of tidal flushing of saline water from the creek would have prevented the growth of the weed. But the scientists were surprised as the analysis showed that the salinity content in the water despite tidal flushing was nil in all three samples.
Fishing nets can be used to remove the weed on a regular basis. “This will remove nutrients from the system and prevent development of anoxia in the water column,” the study states.
CCP had initiated an exercise with four workers to clean the lake. “We used fishing nets and a canoe and removed the weed after four days,” Furtado said.
Residents are keen about the restoration of the lake, a green lung in an urbanized setting. “The water is clear now after removal of the weed and if the saline content is increased, it may not grow,” Ramchandra Deo, a resident said.
Agreed Naqvi, “The lake should not be allowed to die and flushing the lake can help improve the water quality,” he said.
View original article at:‘Excessive nutrients, algal growth choking Miramar lake’