The waters of the St. Lawrence are warming and the amount of oxygen is decreasing

The waters of the St. Lawrence River flow past the city of Montreal on November 11, 2015. (Paul Chiasson, The Canadian Press)

The decline in the amount of oxygen in the seabed of the St. Lawrence River is of concern to researchers from the governments of Canada and Quebec, who on Thursday released the State of the St. Lawrence 2024.

For the period from 2018 to 2022, 18 indicators covering water quality, the biological resources present in the river and the state of its banks were assessed as part of the joint program to monitor the state of the St. Lawrence.

The main conclusion is that "the state of health of the river remains fragile" and certain indicators, such as water temperature and oxygen saturation, show "worrying signs of deterioration."

Warmer water and hypoxia

The document points out that since 2015, temperatures in the deep water layers of the St Lawrence have reached record levels compared with temperatures recorded since 1915.

The average temperature at a depth of 300 metres even exceeded 7 degrees Celsius for the first time in 2022.

The warming of the deep waters, which has been observed for several years now, is contributing to hypoxia and, therefore, to a reduction in the amount of oxygen.

The deep waters of the St Lawrence are a mixture of the warm waters of the Gulf Stream and the cold waters of the eastern Labrador Current.

It turns out that the warmer waters of the Gulf Stream are contributing more and more to the composition of the deep waters of the St Lawrence, and this change "can only worsen the hypoxia situation, since these waters are less rich in dissolved oxygen than the waters of the Labrador Current."

The report also points out that "this change is possibly linked to changes in ocean circulation caused by global warming."

The lack of oxygen in the St Lawrence can have serious repercussions on ecosystems, for example by asphyxiating organisms living on the seabed.

This report by The Canadian Press was first published in French on Sept. 5, 2024.