Imagine a lake so acidic it’s like swimming in battery acid. That’s the reality of Kawah Ijen in Indonesia, a volcanic crater boasting Earth’s largest acidic lake, sitting over 7,700 feet above sea level. This extreme environment, with a pH as low as 0.1, is just one example of the astonishing chemical diversity found in inland waters around the globe, a fascinating subject explored in David Strayer’s new book, *Beyond The Sea: The Hidden Life in Lakes, Streams, and Wetlands*.
While most of us aren’t water chemistry enthusiasts who debate redox reactions over beer, understanding the pH scale is key to grasping the incredible range of conditions supporting life in these environments. pH measures acidity and alkalinity, with 7 being neutral. A shift of one pH unit represents a tenfold change in acidity; a pH of 2.5 (like vinegar) is a billion times more acidic than a pH of 11.5 (like ammonia). This logarithmic scale highlights how seemingly small changes can have profound consequences.
The oceans, for example, are slightly basic (pH ~8.1), but rising atmospheric CO2 from fossil fuel burning is causing a concerning decrease. A drop from 8.2 to 8.1 represents a 26% increase in hydrogen ions, enough to threaten marine life like clams and corals that struggle to build and maintain their shells in more acidic conditions. Ocean scientists are urgently investigating these changes.
Inland waters, however, exhibit a far more extreme pH range than the ocean. While most fall between pH 4 and 9 (a 100,000-fold difference in hydrogen ion activity), some lakes push the boundaries even further. Kawah Ijen’s extreme acidity, rivaling battery acid (pH ~0.7), presents a stark example. Surprisingly, life persists even here: scientists have discovered a green alga and three archaeans thriving in this harsh environment, although animals appear absent. The lake’s outflow stream, gradually neutralizing as it flows, supports chironomid fly larvae where the pH reaches around 2.5.
Remarkably, some species not only survive but prefer these extreme conditions. One archaean found in volcanic waters grows best at pH 0.7 – essentially, battery acid is its ideal habitat! In contrast, alkali lakes (pH 9.5 to 11.5), often found in dry regions where evaporation concentrates minerals, offer another extreme. These lakes, sometimes rich in sodium carbonate, can be highly productive, despite supporting mainly microbial life. Recently, alkali lakes have gained attention as a significant source of lithium, a crucial element in electric car batteries.
The pH range of inland waters – from a minuscule 0.1 to a high of 11.5 – represents a staggering 250 billion-fold difference in hydrogen ion activity. Life, however, has found a way, adapting and thriving across this spectrum. This impressive biodiversity underscores the remarkable resilience of life and the need for conservation efforts to protect these unique and fragile ecosystems. The study of these environments provides invaluable insights into the limits of life and the power of adaptation.
