The decrease in the amount of oxygen in the seabed of the St. Lawrence is a concern for researchers from the governments of Canada and Quebec, who published the Global Portrait of the State of the St. Lawrence 2024 on Thursday.
For the period from 2018 to 2022, 18 indicators relating in particular to 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 health of the river remains fragile” and some indicators, such as water temperature and oxygen saturation, show “worrying signs of deterioration.”
Water warming and hypoxia
The document highlights that since 2015, temperatures in the deep water layers of the St. Lawrence have reached record levels compared to 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 deep waters, observed for several years, contributes to hypoxia, and therefore to a reduction in the quantity of oxygen.
It should be noted that the deep waters of the St. Lawrence are made up of a mixture of warm waters from the Gulf Stream and cold waters from the East Labrador Current.
However, it turns out that the warmer waters of the Gulf Stream are increasingly contributing 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 highlights 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 suffocating organisms that live on the seabed.