Freshwater bodies have become more acidic with rising CO2 levels

A new study has revealed that fresh bodies of water are becoming more acidic. While it is widely known that rising levels of atmospheric carbon dioxide (CO2) have caused significant ocean acidification, this is some of the first evidence to show that freshwater bodies are absorbing extra CO2 as well.

The researchers discovered that some freshwater ecosystems have become more acidic with rising partial pressure of CO2 (pCO2).

In lab studies, the team demonstrated that increasing levels of freshwater pCO2 negatively affect at least one core species. The scientists identified a tiny freshwater crustacean that becomes unable to defend itself after exposure to pCO2.

The findings suggest that increasing CO2 levels may be having widespread effects on freshwater ecosystems. Dr. Linda Weiss of Ruhr-University Bochum in Germany is the lead author of the study.

“Ocean acidification is often called ‘climate change’s equally evil twin,’ and many current investigations describe tremendous effects of rising CO2 levels on marine ecosystems,” said Dr. Weiss. “However, freshwater ecosystems have been largely overlooked. Our data indicate another pCO2 problem: pCO2-dependent freshwater acidification.”

Researchers have shown that ocean acidification can have negative consequences for marine food chains, nutrient cycles,  biodiversity, and overall productivity. Despite all of these potential issues, very little is known about freshwater acidification.

To investigate whether or not freshwater bodies were undergoing a transformation similar to that of ocean acidification, the research team focused a study on four freshwater reservoirs in Germany.

After analyzing over 35 years of data that spanned from 1981 to 2015, the experts confirmed that there has been a continuous rise in pCO2 levels over this time period. The team found that freshwater bodies may even be acidifying at a faster rate than the oceans.

The researchers also developed a study to closely examine the impact of pCO2 on freshwater crustaceans called Daphnia, which are a primary source of food for many larger marine creatures.

Daphnia respond to predators by producing helmets and spikes that make them difficult to eat. The research team found that rising pCO2 levels get in the way of the Daphnia’s ability to put up its defenses.

“High levels of CO2 reduce the Daphnia’s ability to detect their predator,” said Weiss. “This reduces the expression of morphological defenses, rendering them more vulnerable.”

Weiss explained that this phenomenon needs to be studied on a global scale. She said that the findings of the research have raised the question, “Are all freshwater impoundments prone to this kind of acidification?”

The study is published in Current Biology.

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By Chrissy Sexton, Earth.com Staff Writer