Devastating droughts. Massive floods. Melting ice caps. While cataclysmic predictions surrounding climate change make for flashy news, scientist Pascale Biron studies a less showy prospect: the increased movement of sediment in rivers.
A geomorphologist at Concordia University in Montreal, Biron and her team spent five years examining the interaction between the St. Lawrence River and three of its tributaries, the Batiscan, Richelieu and Saint-Francois, which all join the mighty waterway between Montreal and Quebec City.
Of particular interest to Biron was the impact of the movement of sediment on the vast and shallow fluvial lake, Lac Saint-Pierre.
“One of the motivations to work in that area is that it’s a highly sensitive zone,” said Biron. “In terms of wetlands and biodiversity, Lac Saint-Pierre is critical. And of course the St. Lawrence River in general is very important from an economic point of view.”
The just-completed research will soon be published in the journal Hydrological Processes. Among her co-authors was internationally renowned hydrologist Rob Ferguson of Durham University in England, who she met while working on her PhD overseas. Ferguson provided valuable models on sediment transport that she and her team adapted to local conditions.
“What’s amazing is the St. Lawrence River is hugely important, but we have very little information on its tributaries,” said Biron, in her signature British-Quebecois accent. “We had to start from scratch.”
They discovered that flow patterns of this system, established over millions of years, are rapidly changing due to the rising temperatures scientists associate with climate change.
Biron explained that spring thaws now occur earlier, sometimes hitting the region as early as January. The melting snow and ice cause water, silt and sand to surge into the St. Lawrence at a time when it’s typically low. This creates a steeper slope between the bodies of water. Much of the sediment that previously would have remained at the deltas of these tributaries now dumps into the great waterway, and into Lac Saint-Pierre.
Compounding the problem, said Biron, is the fact that the Great Lakes, the primary source of the St. Lawrence, are getting lower as warming trends speed up evaporation.
According to Brent Harris, a ship agent with the international transport company Inchcape, the shipping industry keeps close tabs on decreasing levels in the St. Lawrence. Montreal-bound vessels carry lighter loads, and many ships discharge in Quebec City to avoid shallower waters upstream.
“It’s a very complicated management system in the context of climate change,” said Biron. “When you change the levels of the St. Lawrence, it’s not just a local effect. It’s the whole watershed.”
Biron predicts increased sediment will reduce the area of Lac Saint-Pierre. She believes wildlife that depends on the lake for survival could be threatened, and that floods may have a farther reach, affecting homes and businesses situated well beyond current flood zones.
Professor Mike Stone of the University of Waterloo isn’t surprised by the findings. His research also concentrates on sediment transport. He added another disheartening element into the scenario: when fine sediment makes it way downstream, chemical contaminants tend to join the particles for the ride.
A representative at Fisheries and Oceans Canada, however, was puzzled by Biron’s predictions.
“That’s news to me,” said geographer Richard Sanfacon, who works for the agency’s Hydrographic Service. He coordinates surveys of Lac Saint-Pierre used for annual dredging operations. Sanfacon said that he didn’t have the data to compare levels from year to year, but that his guess is that sediment is actually going down.
“We don’t have enough information to judge the effects of climate change,” said Sanfacon. “And climate change itself is debatable.”
Biron emphatically disagrees.
“There is no debate,” she declared. “All models predict higher temperatures and more extreme weather events. People should just say, climate change is happening, and ask, now what? How do you adapt? It’s not something that will just go away.”