Polluted water making Ganga’s river bed unfit for sustaining aquatic life, says new research

It’s not just the surface, River Ganga is polluted from deep inside, a new research has found. The research by a team of scientists from Banaras Hindu University (BHU) and Mahatma Gandhi Kashividyapith University in Varanasi has found that the river’s underwater has got fragmented, meaning no existence of aquatic life, due to untreated sewage flowing into the river from cities.

The scientists have found millions of litres of waste water, containing toxic elements and metals, is dumped in the Ganga, thereby depleting the level of dissolved oxygen in its water, particularly near the river bed, triggering a condition known as hypoxia, in which marine life cannot survive.

“These hypoxic stretches that can be from 50m to 400m downstream from where a drain is a emptying into the river and are fragmenting the underwater habitat as they become unfit for sustaining life,” said Jitendra Pandey, a professor with the Centre for Advanced Study in Botany at BHU. The findings have been published in Current Science, an Indian peer reviewed science journal, in its December 25, 2019, issue.

The researchers have found that benthic communities - living organisms that inhabit the river bed and river - are particularly under threat. As benthic communities along with planktons (floating microscopic organisms) not just help to keep the river water clean but also support the river’s food chain. Researchers say their absence is threatening the existence of bigger animals such as fishes and dolphins.

The BHU team found such hypoxic conditions at two stretches on the path of Ganga - down stream of Assi drain in Varanasi and downstream of Wazidpur drain in Kanpur.

While the Assi drain carries around 66 million litres (MLD) of domestic waste water into the river, the Wazidpur drain carries around 54 MLD comprising mostly industrial waste. More than 500 water samples collected between April and June for two consecutive years 2017 and 2018 were analysed.

“The level of dissolved oxygen dropped to less than 2mg per litre near the riverbed which is called a hypoxic condition. This is making the water quality at the bottom of the river and the river bed unfit for sustaining life,” said Pandey.

Higher the level of dissolved oxygen, better it is for the aquatic life. For instance, for fishes to survive and humans to bathe, the minimum level of dissolved oxygen required is 5mg/litre.

Experts warned that such conditions are affecting only the Ganga, in which the study was conducted, but all other rivers including Yamuna. In April 2018, researchers from Delhi University had found that for every three kilometres Yamuna travels downstream in Delhi, at least one species of micro-organism, which thrives in unpolluted water, vanishes. Of the 21 major waste water drains in Delhi, 18 fall directly into the Yamuna.

“Sewage water contains several microbes and organic matter. These microbes decompose the organic matter and use the dissolved oxygen in the water. The dissolved oxygen level sometimes becomes nil. The slow moving animals die and the fast moving animals shift to stretches with suitable habitat. Thus, these hypoxic regions become lifeless fragmenting the rivers’ habitat,” said Ravindra Sinha, a professor with the Zoology Department at Patna University and popularly known as the ‘Dolphin Man of India’.

According to BHU scientists and experts, the way to prevent fragmentation of river beds is to ensure ecological flow of the rivers.

“We need the ecological flow of the river to bring down such hypoxic conditions. The waste water needs to be treated in treatment plants before they are discharged into the river. Also we need to construct wetlands which purifies the waste water naturally before it is discharged,” said CR Babu, professor emeritus at Centre for Environmental Management of Degraded Ecosystem in Delhi University.

In January this year, the Central Pollution Control Board (CPCB) published a study titled “Biological Health of River Ganga” which said that there was no improvement in the overall water quality of the Ganga, including in the stretches where Gangetic dolphins are found.

Cleaning the Ganga is one of the flagship projects of the Narendra Modi government. The government has set up the National Mission for Cleaning Ganga and launched the Namami Gange programme in 2015 with a budget outlay of Rs 20,000 crore. It has also framed a draft National River Ganga (Rejuvenation, Protection and Management) Bill.