Photo credit: EPA/Eric Vance

There’s been a lot of stories lately about how human action is impacting the world’s oceans, and with good reason: ocean acidification, coral bleaching, overfishing and pollution are pushing the Big Blue to the brink—throwing entire ecosystems into limbo. But what we don’t hear about as often is how our lakes, rivers and streams are faring in the Anthropocene. Fresh water might account for less than 1 percent of all the H20 on our planet, but without it we wouldn’t be living, breathing and writing on this beautiful world. So, how’s the Earth’s potable life potion doing?

The short answer: not very good. Two studies released this week show that our lakes and reservoirs are acidifying at alarming rates, our rivers and streams are becoming dangerously salty and basic (alkaline), and our drinking water is increasingly at risk of contamination.

“Everyone assumes that we have clean freshwater, clean drinking water,” explained Sujay Kaushal, an Associate Professor at the University of Maryland, who’s research focuses on the chemical composition of fresh water. “But we have to keep pace with pollution sources…to stay in the same place we have to keep running.”

Salty Rivers and Toxic Tap Water

Road salt is loaded into a truck surrounded by mountains of salt at Eastern Minerals Inc., Wednesday, Jan. 3, 2018, in the Boston suburb of Chelsea, Mass. Photo credit: AP Photo/Bill Sikes


It’s horribly, ungodly, unreasonably cold in the U.S. right now. And while this doesn’t mean that climate change is made up, it does mean that if you walk outside there’s a good chance you’ll see salt all over the roadways. These mountains of salt perform an important service (stopping countless car crashes on icy roads), but a report published in the Proceedings of the National Academy of Sciences earlier this week shows that this practice is also compromising the chemical integrity of our freshwater. A team of investigators from various universities in the U.S. used data from hundreds of U.S. Geological Survey monitoring sites, dating back 50 years, to track the salinity level in U.S. streams and rivers. They found that not only is the salinity rising in about 40% of our waterways, but that this increasing salt load is raising the pH of our rivers (as pH increases, water becomes more alkaline, the opposite of acidic).

Both alkalinity and salinity are critical factors when considering water quality, and can impact the animals that live in freshwater ecosystems, as well the potability of the water. “If the water travels through old pipes, that salty water can corrode the pipe infrastructure, and that can stimulate the release of metals [like aluminium, zinc or lead]” explained Kaushal, the lead author of the study. “Saltier water interacts with the old pipes to exacerbate the problem of ageing infrastructure.”

If we want to see the real-world impact of increasing water salinity, we need look no further than Flint, Michigan. When the city switched its water source to the Flint River, the river’s higher salt load meant that more lead leached from water pipes into peoples’ drinking water. And Flint isn’t alone in its old pipe problem: the American Society of Civil Engineers rated America’s drinking water a “D” in the annual report card, largely because of an ageing infrastructure.


Map showing changes in the salt content of fresh water in rivers and streams across the United States over the past half century. Warmer colors indicate increasing salinity while cooler colors indicate decreasing salinity. The black dots represent the 232 U.S. Geological Survey monitoring sites that provided the data for the study. Graphic credit: Ryan Utz/Chatham University

And it’s not just salty roadways that are to blame for the increasing salinity. In the Midwest, fertilizers with high potassium content play a role, and in other parts of the country mining waste and natural weathering of concrete, rocks and soil are some of the main culprits. Whatever the source, these salts come together in our rivers and streams, and form a dangerous, corrosive cocktail.

Kaushal believes that regulating salts as contaminants is a good first step towards fixing the problem. “[Salts] can interact with this ageing infrastructure, we know that they mobilize other pollutants from landscapes, and we also know that there are effects on wildlife and biodiversity,” he said. “And right now, these salts aren’t regulated as primary contaminants to drinking water in the U.S.”


Unfortunately, any new chemical regulations are highly unlikely under the current administration. Even under an environmentally friendly president, getting a new contaminant regulated by the EPA is a long and tiresome process, and Trump’s words and actions have only served to weaken the EPA’s ability to keep America’s drinking water clean.

Carbonated Lakes

Ocean acidification is a relatively well-known phenomenon, but not too much attention has been paid to how freshwater bodies react to all the CO2 we’re pushing into the atmosphere. But a study released this week from a team in Germany worked to fill in this information gap; the study, published in Current Biology, found that the concentration of CO2 in freshwater is increasing at alarming rates, and will likely carry negative consequences for animals that live in these freshwater systems.


By analyzing 35 years of data, the study found that the rate of acidification in freshwater reservoirs was actually occurring faster than it was in the oceans. The paper’s lead author, Linda Weiss from Ruhr-University Bochum, called the findings “astonishing,” and went on to explain that although they had only looked at data for a few select sites in Germany, her team believed this acidification was likely a global phenomenon. “As more CO2 is being pushed into the atmosphere, it has to go somewhere,” she explained “and as fresh water impoundments are important carbon sinks, it’s quite logical that this is a global phenomenon.”

Predator induced defenses in Daphnia longicephala (top row, credit: Linda Weiss) and Daphnia pulex (bottom row, credit: Sina Becker). Left shows an undefended morphotype, right shows the defended morphotype. Insert shows magnification of expressed neckteeth. These morphological features render Daphnia less susceptible to predators. When the expression of these defensive traits is hampered by high levels of CO2, Daphnia is suspected to fall as prey more easily. Photo credit: Linda Weiss and Sina Becker

To test how this increased acidification is impacting animals that live in freshwater bodies, Weiss and her colleagues looked at the case of a tiny freshwater crustacean called Daphnia. “Daphnia are key species in freshwater environments, and they are actually a very important trophic links between producers and consumers,” explained Weiss. Normally, when Daphnia sense that predators are around, they produce little tiny helmets and spikes that make them harder to eat. But Weiss’ team found that as the concentration of CO2 in the water increased, the crustaceans ability to defend itself were greatly reduced.


“If this first level of consumers is not so well defended anymore, this might have cascading effects on further trophic levels,” said Weiss. She went on to explain that given how widespread the impacts of acidification are on marine ecosystems, it’s very likely that increasing CO2 in freshwater will also negatively effect a whole range of organisms.

Wait: Is Freshwater Getting More or Less Acidic?

You might have noticed that the study from Germany is showing almost the exact opposite result as the study from the U.S.: CO2 is making lakes and reservoirs more acidic (lower pH) while salts are making our rivers and streams more alkaline (higher pH). So, wouldn’t this mean the increased acidification in lakes found by the German team would be balanced out by the increased alkalinity in rivers and streams? Unfortunately, it doesn’t seem to work that way.


Kaushal, the lead author of the salt study, explained that a body of freshwater that isn’t moving has the ability to intake CO2, and form carbonic acid, thereby acidifying. But when the water begins to move, such as in rivers, in interacts with chemical substance, like salts and limestone, that act as natural antacids. This works to quickly reduce the acidity of the water, and means that even if lakes are acidic, rivers can be alkaline if they have an overflow of certain chemicals (like salt).

The ultimate takeaway is that we’ve managed to mess up our freshwater systems on both ends of the pH scale: our lakes are too acidic because of CO2, and our rivers and streams are too alkaline because of salts. These changes in pH can carry some pretty nasty consequences, as aquatic creatures have adapted over millions of years to live within a range of pH levels.

“What we’re seeing in these freshwater systems is another factor of climate change, and the effects of our fossil fuel combustion,” explained Weiss. “I would hope that people would start rethinking [their energy use], and especially policy makers, that they take concrete actions to reduce emissions.”


The papers mentioned in this article can be found here:

Current Biology, Weiss et al.: “Rising pCO2 in Freshwater Ecosystems Has the Potential to Negatively Affect Predator-Induced Defenses in Daphnia”

PNAS, Kaushal et al.: “Freshwater salinization syndrome on a continental scale”