- Except for destroying a hydropower undertaking and killing 55 individuals, the October 2023 glacial lake outburst flood in Sikkim additionally left important adjustments in water depth, high quality, and floodplain construction, finds a brand new research.
- The research in contrast the well being of the river pre- and post-flood, and famous that the catastrophe resulted within the “simplification” of the Teesta river’s complicated ecology.
- The adjustments within the river movement regime might hurt keystone species just like the snow trout by way of destruction of spawning grounds, diminished species abundance, and challenges for species migration.
A brand new research printed by researchers from the Indian Council of Agricultural Analysis (ICAR)-Nationwide Bureau of Fish Genetic Sources (NBFGR) reveals the extent of injury brought on by the 2023 glacial lake outburst flood (GLOF) in Sikkim, noting important adjustments in water depth, high quality, and floodplain construction for the reason that deluge.
The GLOF in October 2023 destroyed a 1,200-megawatt hydropower undertaking and killed 55 individuals because it got here cascading down, marking one of many worst disasters the northeastern Himalayan state had seen in latest occasions. Whereas a number of assessments capturing the extent of injury to the state’s infrastructure exist, only some research have evaluated the ecological damages borne by the river.
The ICAR-NBFGR research, printed within the journal Ecohydrology in Could, in contrast the well being of the river pre- and post-flood, wanting particularly at parameters corresponding to deep pool habitats, water turbidity, and provision of ecosystem providers. “We had an ongoing research to seize the range of the Teesta basin when the flood occurred, which is why we have been in a position to examine parameters earlier than and after the flood occurred,” mentioned Rejani Chandran, a senior scientist at ICAR-NBFGR and an creator of the research.
Sujith V. Gopalan, an impartial conservation biologist who was not concerned with the research, mentioned that such assessments are uncommon. Gopalan had authored a post-flood biodiversity influence evaluation in Kerala for World Broad Fund for Nature (WWF India) in 2019. “Our focus typically tends to be on huge mammals and birds. However for the remainder of our lesser faunal teams, there may be little or no understanding of how disasters influence their populations and inhabitants constructions,” he mentioned.
The GLOF in Sikkim resulted within the “simplification” of the Teesta’s complicated ecology, to the detriment of fish species abundance and variety, the ICAR-NBFGR research finds.
Deep pool habitats affected
The Teesta river stretches throughout 414 kilometres, originating in Sikkim and increasing into West Bengal and Bangladesh additional downstream. Its huge elevation vary means it passes by way of totally different climatic zones and hosts a wide range of habitats. Research have recorded not less than 92 species of fish inhabiting the river, together with endangered species just like the Sisor rabdophorus (a kind of catfish) and the “zig-zag eel” (Mastacembelus armatus).
To grasp how the flash flood impacted fish habitats, the researchers in contrast 10 parameters throughout 11 websites because the river passes by way of Sikkim and West Bengal, with 4 websites having a file of pre-flood ranges. In addition they carried out interviews with fishermen, who reported a noticeable decline in fish shares and lack of ecosystem providers.
In line with the evaluation, the gush of water and particles from the GLOF triggered the floodplain space to broaden by 138% and the width to extend from 88 metres to 147 metres in Tanak, the very best elevation level within the research. These impacts taper additional downstream, which “signifies that the detrimental influence…was increased in upstream than in downstream areas,” the research says.
Whereas the river’s floodplain wasn’t uniformly affected, the research discovered that water depth decreased considerably throughout all research websites. Deep pool habitats, that are “distinctive microhabitats that assist wealthy fish range owing to their beneficial purposeful properties,” had disappeared in a number of locations. Greater turbidity after the flood in locations like Joyee Bridge (West Bengal) and Rangpo (Sikkim) lowers transparency and impacts the “general web main productiveness of the system,” the research says.
The adjustments within the river movement regime are more likely to be notably dangerous for keystone species such because the snow trout and flagship species just like the chocolate mahseer, the research notes. Lowered water depth, shifting boulders, and impaired lateral connectivity can result in the destruction of spawning grounds, diminished species abundance, and introduce challenges for species migration. “Our notion of adjustments and impacts as a result of flash flood match with comparable observations made in different research, which we cite,” mentioned Chandran.
Fish just like the mahseer and snow trout are additionally a supply of livelihood for fishers dwelling alongside the Teesta river. In interviews with 13 fishermen, they noticed that bigger fish like Barilius (locallally known as baroli) had migrated to “safer areas” like tributaries and confluence factors, on account of the injury from the flood. “Subsequently, they (fishers) had no selection however to rely on small fish to generate earnings for his or her livelihood,” the research says.
Earlier, fishers would catch three-four kilograms of fish, value ₹700-800. After the flood, nonetheless, fishers mentioned they caught lower than one kilogram, value simply ₹50-100.
Lengthy-term monitoring wanted
The 2023 GLOF was triggered by a landslide, brought on by gradual melting permafrost that in the end resulted in giant chunks of ice falling into the South Llonark lake. The influence triggered a 20-metre tsunami to rise from overfull lake, which then got here cascading downstream. A publish catastrophe wants evaluation of the occasion, mentioned the flood broken 2,004 homes and destroyed 33 roads and bridges.
“When a flood like this occurs, microhabitats the place fish breed, feed, and transfer alongside are all destroyed. The vegetation alongside the banks of the river are utterly eroded. Due to these adjustments, they could even be extra susceptible to assault from predators on account of fewer hiding areas,” mentioned Gopalan. “Lengthy-term monitoring is essential to see whether or not populations are bouncing again.”
Along with the flash flood, local weather change and dams also can have an effect on microhabitats, the research says. Greater than 40 small to medium hydropower tasks are deliberate alongside the Teesta river, the cumulative impacts of which, based on one evaluation, might influence greater than 100 species of fish. The dam that was destroyed within the 2023 flash flood can be awaiting approval to be rebuilt.
“Flash floods are taking place ceaselessly, however there are hardly any baseline surveys to grasp the complete influence they’ve on range. We hope that this research sheds gentle on this side, and gives a baseline for additional research,” mentioned Chandran.
Learn extra: Political stir follows knowledgeable panel’s approval to rebuild Teesta dam in Sikkim
Banner picture: Fishing within the Teesta river in Bangladesh. Picture by Ahamed Rafid by way of Wikimedia Commons (CC BY-SA 4.0).
