Terrestrial oceans absorb about 40% of all carbon dioxide (CO2) emitted into the atmosphere. This CO2 then acidifies the water, which has the effect of harming marine fauna, especially molluscs, in a well-documented phenomenon known as ocean acidification.
Yet, according to a recent study, ocean waters are not the only water bodies affected by CO2 emissions. Freshwater is also concerned.
The study reports that, over a 35-year period, four freshwater bodies in Germany have seen a significant increase in CO2 levels and a decrease in their pH by around 0.3 (the pH varies from 1 to 14, with 1 being the most acidic and 14 being the most basic).
For this study, the researchers analyzed the data collected from 1981 to 2015 by the local Ruhr agency, which monitors drinking water. In doing so, they were able to observe increasing levels of carbon dioxide, taking into account changes in temperature, water density, pH, ionic species distribution, and total inorganic content. Although freshwater systems absorb CO2 in different ways than the oceans, the impact on aquatic life is the same: it is negative.
The team focused on the effects of this acidification on small freshwater crustaceans, namely water fleas. In the laboratory, they then subjected these animals to CO2 levels slightly above the maximum level observed in the world’s freshwater — about 60%. If in oceanic studies, acidification affects the ability of animals to form shells, it appears that in freshwater these small crustaceans are here less able to detect predators and to defend themselves when exposed to higher levels of CO2.
The study of freshwater acidification has so far been delayed for a long time, as determining how atmospheric carbon affects these ecosystems requires a complex process, which yields results that are more difficult to analyze than for the oceans. This result of this research needs further investigation, but it is clear that climate change is contributing to the acidification of oceans and freshwater bodies.