The River Thames in London was so deprived of oxygen in August 2022, due to sewage and hot weather, that it was effectively on life support. new scientist can reveal. A specialized vessel was used to directly inject the gas into the water for 11 days of that month to prevent the death of plants and fish. As temperatures rise due to climate change, this may need to be done more frequently, despite recent efforts to clean the river and improve oxygen levels.
Maintaining healthy oxygen levels in rivers is vital for plant life and fish, he says John Sullivan at Thames Water, the company that oversees the river. But sewage spills and hot weather can cause a dramatic drop. For example, on June 19 of this year, thousands of fish They were found dead in the River Soar in Leicester, UK, due to low oxygen levels.
Hot weather is a factor because water contains less oxygen at higher temperatures, Sullivan says, while wastewater encourages the growth of gas-eating bacteria, plants and algae.
To cope with this, Thames Water operates two boats, the Bubbler and the Vitality, each of which can inject 30 tonnes of oxygen into the river per day.
Last year, Vitality pumped this gas into the Thames for 11 days throughout August, according to a request made by new scientist under environmental reporting regulations, which are designed to ensure that such details are made public. “[This was] due to [low] oxygen levels in the water, as a result of the summer and the buildup of pollution in the water,” says a Thames Water spokesperson.
charles tyler at the University of Exeter, UK, says this injection technique is a “last resort.” “If you have to go to a river and fill it with oxygen to save the lives of fish or invertebrates, it’s crisis management,” he says. “I’m not saying it’s a bad thing, but I think it’s addressing the issue a bit late in the game.”
Both vessels have been in use for decades, but the need for them has been greatly reduced since 2015, when the development of several sewage treatment and overflow facilities reduced the discharge of raw sewage into the Thames by nearly 50 percent. cent, says Sullivan. The boats were used for 330 hours in 2015, but only a few hours in the intervening years, before logging 215 hours in 2022.
Sullivan suggests that a new London super sewer due to be operational by 2025 should stop up to 95 per cent of the overflow of raw sewage into the Thames, which can make ships obsolete.
But climate change could mean Thames Water will have to keep pumping oxygen into the river, Sullivan says. “Warmer temperatures and less rain don’t add up to a good concept for oxygen levels in the Thames,” says Sullivan.