'Nigeen Lake has turned eutrophic'

Greater Kashmir

SKUAST Tests Confirm Physico-Chemical Variations Caused Fish Mortality

Srinagar, Aug 10: Setting all speculations about death of thousands of fish in Nigeen Lake to rest, the Fisheries and Limnological experts of Sher-e-Kashmir University of Agricultural Sciences (SKUAST) Kashmir have said high mortality was mainly caused due to change in the physico-chemical parameters of Nigeen waters propelled by high pollution levels.
Experts from SKUAST have been conducting various tests in the Nigeen since Sunday when the death of large number of fish came to fore. In their preliminarily studies, the experts have detected low dissolved oxygen levels in Nigeen due to eutrophication.
“After comprehensive scientific tests we have found that Nigeen Lake is almost euthrophic. It has high concentration of organic matter. At some places the dissolved oxygen level has dropped from normal to 1.8 milligrams per litre which proved fatal for some species of fish like Crossocheilus Diplochilus and Gambusia Assinis,” Dr Feroz Ahmad Shah, a scientist of Aquatic Animal Health at SKUAST, told Greater Kashmir.
However, he said the native fish Schizothorax was not affected by the process as it prefers to move around springs and cleaner parts of the lake.
Dr Feroz said that two years ago death of fish in large numbers was witnessed in Wullar Lake. “Same species of fish were affected there too. He said Crossocheilus Diplochilus and Gambusia Assinis are mainly found in those parts of a water body which, like Nigeen Lake, have high concentration of mosquitoes as they feed on their larva.
“We have gathered samples of the morbid fish and will conduct histopathological examination of vital parts including liver, kidney and gills for traces of toxification due to metals and other toxic elements present in the water body,” he added.
Dr Adnan Abubakar, a limnologist, and Dr Irfan Khan, a fish genetist, both from SKUAST are part of the studies on fish death in Nigeen.
“The orthophosphate level in the lake is 2.9 milligrams per litre, much higher that permissible one microgram. This signifies that Nigeen has turned eutrophic. The decomposition of organic matter caused hypoxic condition in the water system leading to increase in ammonical nitrogen which is highly toxic for fish. The influx of sewage from Lal Bazar and adjoining areas contributes to pollution level in the lake,” Dr Abubakar said.
He said the summer deweeding can be another cause of depletion in dissolved oxygen because the aquatic plants produce oxygen in the process of photosynthesis.
Dean Fisheries SKUAST, Dr Masud Balki, maintains that ‘summer kill,’ in which a large number of fish die due to increase in temperature, signifies that the water body has become eutrophic.
“Root cause of high mortality of fish in Nigeen Lake cannot be only due to high temperature. Oxygen depletion coupled with high pollution levels cause heavy influx of macrophytes, algae which suck oxygen during night,” Dr Balki said.
Dr Balki said on Sunday when the fish died the weather was cloudy and hence no photosynthesis occurred in Nigeen Lake causing acute deficiency of dissolved oxygen and subsequent death of fish.
He underscored the need for comprehensive studies for long-term conservation of fish and other aquatic species. “In the backdrop of high fish mortality in Nigeen we have started studies and its report will be released in coming weeks,” he added.
For past four days, different theories have been floated about the cause of fish deaths. While the LAWDA maintains that the fish died due to high temperature, the Fisheries Department claims that low oxygen levels triggered by decomposition of obnoxious weeds led to high mortality of fish.
The High Court, monitoring the conservation of Dal and Nigeen lakes, Tuesday directed the Government to constitute a committee of experts comprising experts from SKUAST, University of Kashmir and Fisheries Department to ascertain cause of fish mortality in Nigeen.