More than half of our planet's surface is covered by water, and unfortunately, not every body of water is welcoming to life. In some cases, such as the waters of the Dead Sea, the conditions are so extreme that scientists are still trying to understand how organisms thrive there. In a new study, researchers focused on examining the most acidic natural inland waters on Earth—lakes located in volcanic craters, as reported by Live Science.
One example of such a lake is Kawah Ijen in Indonesia, situated at an altitude of 2,350 meters above sea level. According to researcher David Strayer from Johns Hopkins University, this body of water is considered the largest acidic lake on Earth, with water resembling battery acid.
For comparison, the ocean currently has a pH of about 8.1, indicating it is slightly alkaline. Researchers found that burning fossil fuels has led to a decrease in ocean pH by 0.1 units from the pre-industrial value of 8.2. Furthermore, models suggest that by the end of the century, ocean pH could drop to 7.8. This may seem trivial, but it is not: for instance, the drop from 8.2 to 8.1 represents a 26% increase in hydrogen ions, while a drop to 7.8 would mean an increase of 150%.
Scientists assert that such changes will be significant enough to pose challenges for marine life. For example, mollusks and corals will be among the first to suffer, as it becomes increasingly difficult for them to maintain their shells. Consequently, researchers are trying to find ways to prevent these changes or at least slow them down.
According to Strayer, the most acidic inland waters on Earth are ideal for this, as they represent the most extreme conditions, yet life is still able to thrive there. The researchers focused on lakes in volcanic craters, such as Kawah Ijen in Indonesia—these lakes are so rich in sulfuric acid that their pH can be as low as 0.1.
One might assume that life cannot flourish in such conditions, but samples from the lake revealed the presence of green algae and three species of archaea. However, it is likely that no animals inhabit the lake. Yet the acidic water in its outflow gradually neutralizes as it flows downstream, and researchers discovered larvae of flies known as chironomids living in the stream where the outflow reached a pH of about 2.5. Interestingly, some species not only survive in such conditions but actually choose them. For example, one species of archaea inhabiting the lake can tolerate pH levels below 0 and grows best at a pH of 0.7.
Scientists also studied alkaline lakes, which often have a pH ranging from 9.5 to 11.5. Alkaline lakes typically occur in regions so dry that any water entering the lake evaporates rather than draining away. As a result, minerals dissolved in the water accumulate to very high concentrations, and the bodies of water can turn into saline or alkaline lakes.
One might think that such waters do not host any life. However, previous studies have already shown that very salty and alkaline lakes can still be home to microbes. In fact, alkaline lakes may be among the most productive inland bodies of water in terms of the net biomass produced each year.