Human activity has shifted the chemical composition of our waterways. Now, it’s beginning to corrode our freshwater supply.
A new study has confirmed that in the last 25 years, at least a third of the rivers and streams in the United States have gotten saltier. If nothing is done to curb this trend, the results suggest that more than half of these waterways could contain at least 50 percent more salt than they used to by 2100.
The findings are a major reality check. This extreme level of salt pollution would likely pose a serious threat to freshwater resources, urban infrastructure, and natural ecosystems across the nation.
Not only that, but it would also impact the agricultural industry, doubling the number of streams that are too salty for irrigation, from three to six percent.
Unsurprisingly, the study found several human activities to blame, including the use of fertilisers and de-icing salts, as well as land clearing, fossil fuel extraction, irrigation and even climate change.
“Most of the change is related to increases in human land use, with climate change accounting for only 12 percent of the increase,” the authors conclude.
A study published earlier this year also found that acid rain, caused by human air pollution, can dissolve materials that hold salt, thus contributing to the problem as well.
Whether direct or indirect, in the US, salt pollution is not federally regulated, and state controls can be inconsistent. In certain areas of the country, where pollution is especially bad, some freshwater streams were found to be nearly half as salty as the ocean itself.
“Today, the saltiest streams are in the northern Great Plains,” lead author John Olson, a freshwater scientist at the University of California, Monterey Bay, told PBS.
“Salinity is naturally high, and mining and oil and gas extraction are releasing more salt by exposing new rock and pumping out saline groundwater.”
The effects of salinity are widespread and damaging. When salts, such as sodium bicarbonate and magnesium chloride, make their way into our waterways, it can cause a domino effect, releasing toxic metals from the river soil into the stream itself.
It also makes the water less acidic and more basic. These slight changes may not seem like much, but they can be extremely disruptive to delicate freshwater ecosystems, potentially causing several species to die off, including insects.
Not to mention the impact on humans. In the US, this sort of water contamination already costs billions. In the Colorado River Basin, for instance, salinisation is estimated to cost US$300 million per year, damaging US$176 million of crops and US$81 million of houses.
Plus, it is also expensive for public health. In Flint, Michigan, the excessively salty river water even started a public health crisis that was reported the world over.
When this city began taking water from the Flint River, the water’s high salt content along with chemical treatments corroded the city’s plumbing system, releasing toxic lead into the pipes.
It’s not just the US, either. The consequences of salt pollution stretch right around the world, including Australia and Europe, where bodies of freshwater are becoming increasingly salty, causing severe economic and public health problems.
The new study goes a long way towards understanding the effect that human activity can have on our freshwater supplies – a problem that has only recently been identified and is still poorly understood.
“The predictions of increasing salinization of streams and rivers highlight the need for effective management and regulation to ensure we protect water resources and freshwater ecosystems,” the authors conclude in the study.
Outrunning our problems will be a lot harder if we get dehydrated.
This study has been published in Royal Society B.