Carbon acidification could cause problems for Great Lakes wildlife
ARENAC COUNTY — Available data from the Environmental Protection Agency suggests the Great Lakes could be soaking up carbon dioxide in the atmosphere, which could change the pH levels in the water and have a negative impact on wildlife.
Galen McKinley, ocean sciences professor at the University of Wisconsin-Madison, said while data is currently limited, computer projections suggest the Great Lakes’ waters are becoming more acidic due to human carbon emissions. She said a similar process is happening in the open oceans.
According to data from the National Oceanic and Atmospheric Administ-
ration, when carbon dioxide in the atmosphere gets absorbed by bodies of water, the ensuing chemical reaction will reduce the pH level in the water. The pH level of a liquid indicates how acidic or basic it is on a 0-14 scale, with water usually measuring at 7 — perfectly neutral. Lowered pH levels should not impact the drinkability of the water in the lake, McKinley said.
McKinley said the open oceans have faced a 30-percent increase in acidity since the Industrial Revolution, and the NOAA estimates that with current carbon emissions, by 2100 the ocean surfaces could be 150 percent more acidic than pre-industrial levels.
McKinley believes the Great Lakes, and smaller inland lakes, could be facing the same issues on a smaller scale. She said Lakes Michigan, Superior and Huron have long residency periods — water tends to stay in the lake for 100-200 years before moving elsewhere in the watershed. She said that means they tend to be in equilibrium with atmospheric carbon dioxide levels.
“If you just think about the chemistry of carbon and water and about what we know about the Great Lakes, they are more or less responsive,” McKinley said. “They are in equilibrium with the atmospheric carbon dioxide, so the carbon dioxide in the water will also increase and the pH will go down, similarly to the oceans.”
Lakes Erie and Ontario have shorter residency periods for water, so McKinley believes atmospheric carbon dioxide should have a lesser impact, but she thinks they will still feel the effects. She added that most of the data researchers have comes from Lakes Superior and Michigan, and data on the other three lakes is more limited.
A lowered pH can also see lowered carbonate ion levels, which could affect ecosystems in the lakes. The carbonate ion is important for the formation of calcium carbonate minerals, which organisms like mussels and oysters use to develop their shells.
The biological impact of a lower pH level is unknown for the Great Lakes specifically, but McKinley said based on the data from the oceans, some species, such as algae, would thrive, while others, such as mussels, would suffer. While that would help with eliminating invasive mussels, McKinley believes the native species will suffer too.
“There are also concerns in the open ocean (with the impact) on juvenile fish in particular,” she added. “It doesn’t seem to impact adult fish, but juvenile fish tend to be more negatively impacted by lower pH, just as kids are more affected by environmental changes than adults are.”
She said with biological activity, the pH levels in a spot that gets tested throughout the summer in Lake Superior can fluctuate .07 pH units over the course of one week. Despite the variability, she said an overall shift in the average pH can spell trouble for biodiversity in the lakes.
McKinley said knowing how carbon dioxide interacts with bodies of water, the lakes should be becoming more acidic.
“We can’t say if it’s changing, but we have evidence (that it) should be, so I think it’s evidence that we should be taking high-quality measurements so we can begin to answer that,” she said.
McKinley said the problem with determining exactly what the impacts will be in the lakes is a lack of data. While open-ocean studies have been ongoing for years, the Great Lakes get little more than a biannual week-long EPA survey — in April and August — and McKinley believes that is too small an amount of time, and too small an area surveyed, to paint a better picture of the lakes’ health.
“They do a good job of capturing spatially what the lakes’ chemistry looks like over the course of the week, but we’ve shown that you can’t just average it and get a good estimate of the whole year. The lakes are more complex than that,” McKinley said. “There are also some methodological issues, as it’s really a water quality test. It’s not a highly precise estimate for looking at long-term trends.”
McKinley said researchers could borrow some techniques used in the open ocean, such as bottling water samples and measuring the amounts of dissolved carbon and the alkalinity of samples. NOAA buoys could be outfitted with instrumentation to keep track of pH levels, and more testing equipment could be placed in the lake and checked regularly. Her research team has submitted a proposal to the National Science Foundation, but due to the federal government’s sequestration, she does not know when she will hear back about it.
The impact on the broader watershed — smaller lakes and rivers — is harder to predict due to a lack of data, McKinley said. She believes degassing from the landscape tends to make the carbon dioxide levels in those bodies of water naturally higher.