The dissolved oxygen level is in free fall in the St. Lawrence River.
The dissolved oxygen concentration obtained by the most recent research in the deep waters of the St. Lawrence River is the lowest ever recorded. This concentration at depths of more than 250 m in the lower estuary has fallen below 10% compared to surface water in contact with the atmosphere. This threshold represents a very high hypoxia considering that at a concentration of 20% it is already a severe hypoxia.
Dissolved oxygen in the waters of the St. Lawrence is an essential element for all underwater life and the drop in its concentration represents a threat to several species and a. loss of biodiversity that increases with this drop. If the oxygen concentrations continue to drop at this rate in the waters of the river, it is possible that the waters will become anoxic, that is to say devoid of oxygen. This effect would be catastrophic for marine ecosystems and could enrich these waters with toxic heavy metals and dissolved sulphides due to the oxidation of organic matter by bacteria.
The global temperatures rise with climate change is one cause of this effect, the other is the high presence of nutrients, such as nitrogen and phosphorus, from wastewater discharge. The warmer the water, the less oxygen that can be dissolved. So if nothing is done, these conditions will continue to worsen in the coming years.
To find out more, read the article of November 25, 2021 in Le Devoir » (in French)
