Atmospheric carbon can make lakes more acidic

TRAVERSE CITY, Michigan (AP) — The Great Lakes have endured a lot over the last century, from supersized algal blobs to invasive clams and blood-sucking sea lampreys that nearly wiped out fish populations.

Now another danger: They — and other great lakes around the world — could become more acidic, which could make them less hospitable to some fish and plants.

Scientists are building a sensor network to discover trends in Lake Huron’s water chemistry. It’s a first step toward a hoped-for system that would track carbon dioxide and pH in all five Great Lakes over several years, said National Oceanic and Atmospheric Administration co-project leader Reagan Errera.

“When you change things chemically, you change how things behave and work, and so does the food web,” says Errera, a research ecologist at NOAA’s Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan.

“Does that mean your favorite fish might be gone? We don’t know, but we know things will change. Maybe where and when they spawn, where they are, what they eat.”

Oceans become more acidic as they absorb carbon dioxide pumped into the atmosphere by human activity – the main driver of climate change. Acidification endangers coral reefs and other marine life.

Computer modeling studies suggest the same could happen in large freshwater systems. But few programs do long-term monitoring to find out — or to examine the ecological ripple effects.

“This doesn’t mean the waters will be unsafe to swim in. It’s not like we’re making superacid battery fluid,” said Galen McKinley, a professor of environmental sciences at Columbia University. “We’re talking about long-term environmental changes that are imperceptible to humans.”

A 2018 study of four German reservoirs found that since the industrial revolution, their pH levels had fallen three times faster — moving closer to acidity — than in the oceans in 35 years.

Researchers say that by 2100, the acidity of the Great Lakes could also approach around the same rate as in the oceans. Data from the Lake Huron project will help determine if they’re right.

Two sensors are attached to a floating weather buoy at Thunder Bay National Marine Sanctuary near Alpena, Michigan. One measures the carbon dioxide pressure in the water column and the other the pH. In addition, crews are collecting water samples at various depths within the 4,300-square-mile (11,137-square-kilometer) area for chemical analysis.

In addition to disrupting aquatic life and habitat, acidification could affect hundreds of wooden shipwrecks believed to lie on the bottom, said Stephanie Gandulla, the reserve’s resource conservation coordinator and co-leader of the study.

Other monitoring stations and sampling locations are planned, Errera said. The goal is to take baseline measurements and then see how they change over time.

Data is also needed from Lakes Erie, Michigan, Ontario and Superior, she said. They are all part of the world’s largest surface freshwater system, but have different characteristics, including water chemistry, nutrients and other conditions necessary for healthy biological communities.

Acidification from carbon dioxide overload in the atmosphere is different from acid rain caused by sulfur dioxide and nitrogen oxides from burning fossil fuels to generate or produce electricity.

Although acid rain is more powerful, it covers relatively small areas and can be reduced with scrubbing equipment, as required by the US Clean Air Act. But the effect of carbon-related acidification is global and potentially more damaging because there is no easy or quick solution.

“The only solution is a global solution,” McKinley said. “Everyone is reducing their emissions.”

No matter how well countries do at that, large lakes are likely to continue to acidify as they absorb carbon dioxide already in the atmosphere, plus carbon-laden water that drains away from the land, she said.

Less certain are the effects on ecosystems, although initial studies have raised concerns.

Based on lab tests, scientists documenting the rising acidity in Germany’s reservoirs found that it could endanger a species of water flea by hindering its defenses against predators. The small crustaceans are an important food for amphibians and fish.

Scientists in Taiwan experimented with Chinese mitten crabs, an Asian delicacy but an invasive species elsewhere. Raising the acidity of the water in lab tanks to projected levels of 2100 more than tripled their mortality rates, according to a report last year.

Other studies have shown that freshwater acidification impairs the development and growth of juvenile pink salmon, also known as humpback salmon, an important commercial and sport fish species in Alaska and the Pacific Northwest.

But it’s not known how big such problems will become, says Emily Stanley, a professor of freshwater ecology at the University of Wisconsin.

“I honestly don’t see this as something we as lake scientists should go crazy over,” said Stanley. “There are so many other challenges for lakes that are bigger and more direct,” such as invasive species and harmful algae.

Many lakes emit more carbon dioxide than they absorb, she said. But other scientists say even those could acidify because their outflow will slow as atmospheric concentrations rise.

Either way, tracking lake carbon dioxide levels is a good idea because the compound is fundamental to processes, including photosynthesis, that algae and other aquatic plants use to make food, Stanley said.

A critical question is the effect of CO2-related acidification on microscopic plants called phytoplankton, said Beth Stauffer, a biologist at the University of Louisiana at Lafayette who studies the situation around estuaries where fresh and ocean waters meet.

Studies suggest that some of the tiniest phytoplankton can thrive in acidic waters, while larger species – more nutritious for fish – are fading away.

“It’s like walking into a buffet and instead of the salad bar and roast turkey, all you have is cones,” Stauffer said.

Of particular interest to the Great Lakes are quagga mussels, said Harvey Bootsma, a University of Wisconsin-Milwaukee scientist. The prolific invaders have pushed aside other plankton eaters and fueled nuisance algae. Acidification can weaken quaggas’ calcium carbonate shells, as is the case with ocean mussels and clams.

But that’s hardly a silver lining, Errera said. The same fate could befall native mussels that conservationists are trying to protect.

The potential upheaval in freshwater ecosystems is one of many examples of the long reach of global warming, she said.

“Those greenhouse gases that we put into the atmosphere have to go somewhere,” Errera said. “The oceans and large freshwater bodies are where they go, and acidification happens as a result.”

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Follow John Flesher on Twitter: @JohnFlesher

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The Associated Press’ climate and environmental coverage is supported by several private foundations. Read more about AP’s climate initiative here. The AP is solely responsible for all content.

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