Water turbidity hits aquatic fauna
The fish population in the Brahmaputra River in and around Guwahati has drastically decreased after the water turned muddy, a study has revealed.
The study, was conducted by Aaranyak, said “As opposed to normal average of 30 to 45 kg of fish caught daily by one fisherman during the winter season, after the increase in turbidity, it has decreased to five to 15 kg per fisherman.”
The fisherman bycatch is one of the popular sample sizes that are used to measure the fish population in a particular area.
According to Abdul Wakid, Head of Aaranyak’s Gangetic Dolphin Research and Conservation Initiative, who conducted the study, fishing is highest on the Brahmaputra during the winter season.
“In the summers or the monsoons, the river water is too turbulent for fishing. But during the winter, fishing is very rampant in the river. The study also revealed that as per our old data, at least 50-60 fisherman operate around the city in this season, but now the number of fishermen has gone down to about 10-15 whom we have encountered during the time period of a week,” Wakid told G Plus.
The study however did not notice any large-scale fish mortality caused due to the rise in turbidity. Another environmental expert, Jayaditya Purkaystha explained that the turbidity will impact the fish population as it decreases the amount of dissolved oxygen in the water.
“With more pollutants in the water, the dissolved oxygen volume in the water decreases. This won’t impact the amphibians or the cetaceans (aquatic mammals such as river dolphin), but the fishes will be affected. Though there have not been any instances of fish mortality, a study throughout the stretch of the river will reveal that the fish are getting suffocated and will soon die if the condition continues,” Purkaystha said.
Bharalu contamination a bigger threat: experts
While the turbidity of Brahmaputra River has become a major concern, environmental experts are more worried about the contamination in the Bharalu River and the lack of a sewage treatment facility in the city.
“The sudden rise in turbidity is a very recent phenomenon, while the city aquatic life is getting hampered on a daily basis due to widespread chemical and biological wastes dumped on the Bharalu river,” Jayaditya Purkaystha, who is also the founder of a city-based NGO Help Earth ,said.
According to the data released by the Central Pollution Control Board in 2010, the level of faecal coliform bacteria that causes water-bourne diseases such as diarrhoea was below the acceptable norms in the rest of the state but above 3,000 in the city where the Bharalu meets the Brahmaputra.
Besides the CPCB, the Pollution Control Board, Assam, has said the bacteria level of the river is way above the standard norms, caused by the continuous dumping of sewage.
“The situation has worsened. Now, the bacteriological oxygen demand (BOD) level is much higher in the lower streams of the river and its tributaries. If the contamination level rises over the next decade, the Brahmaputra will become another Ganga,” warned Rafiqua Ahmed, chief environmental scientist of PCBA.
The BOD measures the quality of river water especially the population of coliform bacteria or disease-causing bacteria per 100ml of water.
“Had there been proper sewage treatment, not only the BOD but the Chemical oxygen demand, that measures the chemical contamination of the river could also have been brought down,” Ahmed added.
Last month, the water of Siang River in Arunachal Pradesh which is called Yarlung Tsangpo in Tibet and a major tributary of the Brahmaputra, turned muddy fuelling speculation about large-scale constructions in the upstream of the river in China. Arunachal Pradesh Chief Minister Pema Khandu declared the water “unfit for consumption” in the hill state. The Guwahati Municipal Corporation (GMC) that treats and supplies the Brahmaputra water to thousands of citizens in the city found it to be “abnormally turbid”.
China has categorically denied construction of a tunnel for diversion of the river water. But the increasing concern has compelled Assam Chief Minister Sarbananda Sonowal to urge the central government to take up the matter with China.
Soumyadeep Dutta, member of another NGO Nature’s Beckon said, “It is essential to find out what kind of pollutant the turbid water of Brahmaputra consists of. If it is just mud and soil, it is not that dangerous, but if it contains chemical wastes, then it will have a far cascading effect than expected.
“But untreated water from Bharalu is contaminating the river water around the city. In the 1 and half kilometer radius of Bharalumukh, there is no sign of aquatic fauna,” Dutta said.
Lesser fish in the city markets
The decrease in fish population is evident from the lack of river fishes in the city markets, fish sellers shared.
“We are facing a tough time to get river fishes which is in usually in abundance during this time such as Hilsa, Chital or Bowal (Wallago catfish). The market is flooded with Katla, Rohu, Grass carp and other breeds that are reared in stagnant fresh water bodies,” Aminul Laskar, a fish seller at the Uzan Bazar fish market said.
The concern is echoed by a buyer, Chandan Goswami, who had to settle for an overpriced Rohu after days of searching for the Chital. “Chital is available but very expensive. It used to be much cheaper during this season,” he said.
Facing huge losses, the sellers shared that if the crisis persists for more than another week, they will have to seek government’s intervention.
An official of the Assam Fishery department said, “Currently the bulk of the supply is from the government fisheries. But, if this continues and the government’s sources are depleted, then the city fish market will have to rely on the frozen fishes coming from Andhra Pradesh.”
“After all, it is government’s responsibility to maintain the flow of fishes in the city. At an average, the city consumes at least 2,500-3000 kilograms of fish daily. If naturally it is not available, the government will have to make other arrangements,” a seller said.