A paper that was first drafted in a bar in Mont-Joli has been recognized by Quebec Science Magazine as one of the top 10 discoveries in 2011. The paper, written by McGill earth and planetary science professor Alfonso Mucci, is the result of a study on water quality in the St. Lawrence.
Mucci compared historical measurements—specifically dissolved oxygen concentrations and pH—with his own data to get a picture of how the river has changed over time. His results show that the deeper waters of the lower St. Lawrence have become steadily more acidic.
Studies like Mucci’s are giving scientists the chance to look at how changing atmospheric conditions and oceanic currents will affect the oceans of the world and their ecosystems.
“[What is] really neat, but nearly catastrophic, is that what we’re seeing in the St. Lawrence now is what’s predicted to happen to the ocean by the end of the century. We’re getting an early glimpse of how the ocean will respond to this acidification,” he said.
In 2002, Mucci began to study the oxygen levels in the St. Lawrence River. He discovered that oxygen concentrations had been decreasing gradually for at least one hundred years.
Oxygen concentration is part of a chemical balance in the water related to CO2 levels. An important effect of high CO2 (and low oxygen) levels is acidification. When CO2 dissolves in water it becomes an acid; any Coke and Mentos demonstration will show this in action. The Coke is acidic because of its carbonation, Mentos are basic, and the results of combining an acid and a base are explosive.
Hypoxic (low oxygen) zones under water are deadly to marine life.
“Cod can’t live for more than 90 minutes under those [hypoxic] conditions,” Mucci said.
Although fish can swim to better waters, shellfish and other bottom-dwelling sea creatures are not so lucky.
In the St. Lawrence Estuary, the lower oxygen levels are largely the result of changing ocean currents. The young, cold, oxygen-rich waters from the Labrador Sea that used to wash into the estuary have been replaced by warmer central Atlantic waters that are oxygen depleted.
The reason for the shift is hard to pinpoint because of the complexity of ocean current systems. But worryingly, a climate change model developed at Princeton University suggests that the Gulf Stream is shifting northward, meaning that the St. Lawrence Estuary may be receiving more central Atlantic waters in the future.
The problem is aggravated by an increasing demand for oxygen in the estuary. Over the last 80 years, the St. Lawrence has become much richer in organic matter, fed by municipal and industrial waste. These nutrients feed thriving plankton and bacteria communities that require increasing amounts of oxygen as their populations grow.
The result is a big change in chemical balance that hits the bottom of the water column hardest. “You are literally adding acid to the water. So the waters have become acidified about four to six times more rapidly than the surface ocean waters in equilibrium with the atmosphere,” Mucci said.
Acidification in the bottom waters is bad news for creatures like bivalves such as mussels and clams, as well as crab. Bivalve shells are made from calcium carbonate, a basic material. Crab use the same material to patch their battle wounds.
“The [water’s] pH is such that these minerals are no longer stable, so basically their shells dissolve,” Mucci said.
His work has spurred research into the biological impact of the acidification. Partnering with microbiologists from Concordia and biologists at Laval University, Mucci is now studying the effects from the bottom up by looking at bacteria and phytoplankton.
“We’re looking at how more acidic waters will impact their productivity … and how that impacts the rest of the food chain.”
