Oxygen level in the St. Lawrence Estuary concerns researchers

Rimouski, QCAccording to recent data collected by the Department of Fisheries and Oceans (DFO), the levels of oxygen in some areas of the St. Lawrence Estuary have markedly decreased. The hypoxic (low oxygen level) zone is currently covering at least 1300 km2 of ocean floor offshore of Tadoussac and Rimouski. This zone is showing a decrease of animal life since the levels of oxygen are too low to maintain fish, bivalves or crustaceans. Several researchers met last week during a workshop on this issue that was held during the last meeting of the Association francophone pour le savoir (Colloque – À bout de souffle – Raisons et conséquences de la baisse d’oxygène dans les milieux aquatiques).

stlawrence_O2 level_DFO

O2 saturation levels in the St. Lawrence river – DFO

The causes and impact of these changes are not well understood. A decrease in the input of well oxygenated cold water from the Labrador stream has been identified as a potential explanation for the situation. The relationship between this and climate change remains unclear. The release of nitrates and phosphates into the Estuary from agricultural activities, which could promote the growth and proliferation of phytoplanktons, might also play a role in the development of this hypoxic zone. When this phytoplankton dies it gets deposited on the ocean floor where its decomposition would cause a decrease in the oxygen levels.

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