GUWAHATI, Jan 6 - Alarmed at the unnatural death of fish at Deepor Beel, the Pollution Control Board, Assam will conduct an intensive investigation to unearth the causes of the abnormal phenomenon at the Ramsar site.
�An intensive exercise will be carried out after Magh Bihu. The Fisheries Department, Forest, Veterinary departments will lend the necessary support,� a PCBA official told The Assam Tribune.
Samples will be collected during day night hours from all areas of the lake. The scientific officers are likely to stay at the freshwater lake overnight for conducting the tests.
Following the recent fish deaths, some preliminary tests were conducted by the PCBA officials, but they had only baffled the experts as the chemical tests did not point to any abnormality that could cause the fish deaths.
Nineteen tests were conducted in samples of water collected from five different sites � midpoint of the beel, near the MSW (municipal solid waste) dumping site, confluence with Basistha-Bahini river along with Mora Bharalu, water from Basistha Bahini river along with Mora Bharalu before confluence and from near Khonamukh Bridge. The tests had pointed at higher pH level in one part and higher organic load in another.
The pH value of the samples collected from the confluence with Basistha-Bahini river along with Mora Bharalu was found to be on the higher side � 8.9, the permissible limit being 6.5-8.5. The Biochemical Oxygen Demand, which is a measure of quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter, was also on the higher side near Khonamukh Bridge.
But the dissolved oxygen level was found to be sufficient for survival of fishes. Free ammonia and residual chlorine found in the samples were not sufficient to cause the fish deaths. The concentration of none of the parameters, including toxic metals tested, can contribute to the fish deaths, officials who conducted the tests said, adding that the chemical tests were unable to correlate with the fish deaths.
The bio-assay test conducted near the MSW dumping site also did not point to any abnormality. A bioassay involves the use of live animal or plant (in vivo) or tissue or cell (in vitro) to determine the biological activity of a substance.
�There may be some other external agents which may be responsible for fish deaths in Deepor Beel. This needs to be further investigated,� the PBC said in its report to the district administration. �But, we have observed some algae growth in some parts of the Beel. In the event of such growth, there is a possibility that the oxygen level in these parts may decrease drastically during night time. But we will have to conduct some intensive tests to know the exact cause of the fish deaths,� the official said.
There are also reports that some unscrupulous fishermen sometimes use poisonous substances or herbs to kill fish.
The district administration had recently reviewed the situation at Deepor Beel with officials of various departments, including the PCBA, after which the intensive monitoring exercise was decided.
The 4,000-ha permanent freshwater lake is of great biological importance and also essential as the only major storm water storage basin for the city of Guwahati. The beel is a staging site on migratory flyways and some of the largest concentrations of aquatic birds in Assam can be seen, especially during winters. Some globally threatened birds are also supported here.