Sasthamcotta Lake managed to remain a freshwater body for long owing to the virtual absence of nutrients in it. However, the continuous degradation of the lake has resulted in the entry of nutrients into it. This will lead to a big change in the chemical composition of the lake, including the threat of salinity in the long run, environmentalists say.
It was the lack of nutrients that prevented the growth of algae in the lake. This was enabled by the fact that underground springs, seepage of filtered water from surrounding hillocks, and rain were the lake’s main sources of water. The lake also maintained its level through a subsurface flow into the Kallada river which flows nearby.
But wanton unauthorised sand-mining in the proximate areas of the lake has damaged the sources of the water and resulted in a fall in the water level. Instead of feeding the lake, the water from the sources is now flowing into the gaping ravines created around the lake by the sand-mining. There has also been a big drop in rainfall this year.
A study conducted this month by the Kerala Sasthra Sahithya Parishad (KSSP) shows that the water level in the lake that stood at 15.67 metres in December 2010 has fallen to 11.9 metres. The area of the lake that was about 4.50 sq km in the late 1970s has fallen to 2.5 sq km.
KSSP environment committee chairman K.K. Appukuttan and convener V.K. Madhusudhanan said this fall in water level had enabled nutrient-rich water from the nearby Karali marshes on the southeastern side of the lake to flow into it. If allowed to continue, this phenomenon would spell doom for the lake, Dr. Appukuttan said.
The nutrient-rich water from the marshes will trigger algal bloom in the lake.
Mr. Madhusudhanan said an algal bloom could cause eutrophication in the lake and trigger anaerobic conditions.
If unchecked, the process could choke and destroy the lake within a few years. It was a pity that the lake faced such a fate during the 10th anniversary of its being declared a Ramsar Site, he said. It reflected the fact that nothing much had been done during the past 10 years to protect and conserve the lake despite the fact that it was the main drinking water source for Kollam city and seven grama panchayats.
The algal growth in the lake has already lent a green hue to the lake in some pockets, and this is causing unusual sedimentation in the Sasthamcotta water treatment plant and in the overhead water tanks fed by the treatment plant.
In order to overcome this, water is now being treated with alum and calcium, apart from chlorine.
Waste water after this treatment is pumped back into the lake. Dr. Appukuttan said this meant that the lake was getting polluted by two new chemicals, and it would take time to understand in what way this pollution was going to affect the lake.
