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The majestic St. Lawrence under threat 

By Louise Hénault-Ethier

The St. Lawrence is arguably this country’s most economically important river, but it is much more than a waterway for international cargo boats.

Efforts to protect it have considerably improved its health in recent years, but the challenges are increasing. Climate change is inducing alterations of the global ocean that have resulted in warmer, oxygen-poor waters entering the St. Lawrence Estuary.

Some threats, such as dredging to facilitate commercial navigation and deterioration of the shoreline, are highly visible. But subtle chemical changes that cannot be perceived with the naked eye are buried deep below the surface.

Changes in land use as well as deforestation and intensive agriculture can lead to an input of fresh nutrients from runoff. Phytoplankton, consisting of microscopic algae, rapidly take advantage of this novel food source and bloom in the surface waters. When these micro-organisms die, they sink to the bottom of the water body.

When decomposer microbes break down this organic matter, they release carbon dioxide and consume oxygen. If the nutrient input is high enough, and the phytoplankton bloom reaches a great magnitude, oxygen consumption can reach a rate that can deplete the lower layers of a body of water. When oxygen levels become insufficient to support most animal life, the water is defined as hypoxic.

Over 200 hypoxic coastal zones have been identified around the world, notably the Gulf of Mexico and Chesapeake Bay, which are now considered “dead zones.”

Several years ago, researchers discovered that the bottom water of the St. Lawrence Estuary between the Saguenay Fjord and Pointe des Monts was also hypoxic.

The Hypoxia Research Group, a multidisciplinary collaboration between scientists from Concordia, McGill, Université Laval, UQÀR, and the Institut Maurice-Lamontagne of the Department of Fisheries and Oceans, is investigating this recent development to understand its origins and how it will affect the ecosystem as a whole.

With our growing awareness of global warming and fresh water protection, we need these specialized chemists to understand how nutrients cycle in ecosystems in order to better predict the future effects of climate change. Governments need sound scientific recommendations on the natural carbon cycles to plan for the recovery of the St. Lawrence Estuary.

Organic geochemistry is a relatively young field that aims to understand how the biological, chemical and geological processes interact.

Yves Gélinas, from the Chemistry and Biochemistry Department, is a leader in environmental organic geochemistry. He and his group study natural aquatic ecosystems from a chemical point of view. One of their projects is the study of the hypoxic zone of the St. Lawrence.

Unlike their colleagues in the department, who for the most part can grow or synthesize the samples they study, these environmental geochemists need fresh samples collected directly from the environment.

In May 2007, Gélinas, together with PhD student Robert James Panetta, Denis Brion and me, spent a week on board the R/V Coriolis II, a 50-metre Canadian Coast Guard vessel converted into a research boat to navigate the St. Lawrence between the Île d’Orléans and the Cabot Strait.

The team collected numerous water and sediment samples, which will be analyzed in great detail in coming years to uncover the mysteries of the carbon cycle in this ecosystem and how it pertains to the oxygen diminution.

The group patiently filtered hundreds of litres of water sampled at different depths and geographic locations in the river to collect particles and dissolved molecules. They also tediously sliced, packed and labelled hundreds of vials of mud carefully collected from different depths of the riverbed. With their collaborators, they wish to provide the first 3D analysis of organic matter fluxes and sinks in the St. Lawrence.

These people passionately seek to understand their world better in order to protect it. The St. Lawrence is a jewel that deserves their expert attention.

Louise Hénault-Ethier has just completed her MSc through the Special Individualized Program. Her research was conducted partially under the supervision of Yves Gélinas. She is a founding member of the award-winning R4 Compost program.