Grant: Strategic Projects - Group

The state of health of the Gulf of St. Lawrence, a vast ecosystem on the east coast of Canada, has been declining for the last 70 years: there has been a steady decrease in availability of dissolved oxygen to the organisms that live in and use the sea floor and the deep bottom water. The bottom water originates in the slope region of the Western Atlantic Ocean. As this water journeys landward, respiration in water column and sediment consumes oxygen. The bottom water is isolated from the atmosphere, so the lost oxygen cannot be replaced except by slow diffusion from the overlying water. Today, the bottom water of the Lower St. Lawrence Estuary is severely hypoxic, a condition defined by oxygen levels lower than 20% of what is found in water saturated with oxygen. Hypoxic bottom waters (less than 30% saturation) also exist in the head regions of the Anticosti and Esquiman Channels. We attribute one half to two-thirds of the declining oxygen levels to changes in the circulation pattern in the northwest Atlantic ocean, which determines the oxygen content of the water mass entering the deep Gulf environment. The remainder is attributed to the increased flux of organic matter to the sea floor. If oxygen levels in the Gulf of St. Lawrence continue to decline, today's hypoxic waters may become anoxic and the bottom environment may become a "dead zone". Even if we do not reach anoxia, progressively lower levels of oxygen may reduce the area of suitable habitats for many species of demersal and benthic animals, including fish and crustaceans. The proposed research addresses the strategic importance of being able to understand and predict causes and effects of low dissolved oxygen levels in the Gulf of St. Lawrence ecosystem. The project further aims to develop remediation strategies, be they directed towards management of nutrient discharge via the St. Lawrence River or direct injection of oxygen into bottom waters. The proposal combines field observations, laboratory experiments, and modelling, and its goal is to develop tools that can be used to predict future changes in the oxygen regime and the effects of these changes on ecosystem processes and fisheries resources.