Earth's oceans absorb about 40% of all the carbon dioxide (CO2) that humans emit into the atmosphere. That CO2 then acidifies the water and is known to harm marine wildlife, especially shellfish, in a well-documented phenomenon known as ocean acidification. Yet according to a new study published in Current Biology, ocean waters are not the only bodies of water that are affected by CO2 emissions.
Researchers showed that, over the course of 35 years, four reservoirs in Germany had both a significant increase in CO2 and a related decrease in pH, with waters dropping by about 0.3. (pH runs on a scale of 1 to 14, with 1 being the most acidic and 14 being the most basic.) They detected these changes from data from the local Ruhr region agency, which monitors drinking water, over the years 1981 to 2015.
Through these records, the team was able to determine that CO2 levels were rising by noting changes in temperature, water density, pH, ion species distribution, and inorganic content.
Until now, the study of freshwater acidification has been difficult at best. This is because showing how the impact of carbon dioxide on ecosystems demands complicated modeling, and results are typically less clear than when studying ocean systems.
It is likely, according to this study, that freshwater systems absorb CO2 in different ways than oceans do. While the details of these processes are not the same between fresh and saltwater bodies, they share an ability to negatively impact aquatic life.
To explore this further, the team documented the effects of this acidification in freshwater crustaceans —two species of Daphnia, which are known as water fleas. In ocean studies, acidification affects animals' abilities to form shells, but these freshwater species had before not been studied. This team found that these crustaceans, when exposed to higher levels of CO2, were less able to sense predators and defend themselves.
This body of research still needs further exploration, but it is clear that climate change is contributing to acidification in freshwater bodies of water as well as the oceans. There is one spot of hope: it has been suggested by some studies that this process could be mitigated in the ocean. As such, it is not out of reach to suggest that, as efforts to curb climate change continue, information like that found within this study could be used to do the same in freshwater.