Human activities are making the world’s air, soil and fresh water saltier. If current trends continue, this could pose a serious global threat. This is the conclusion of a new scientific study recently published in Nature Reviews Earth and Environment.
According to Geology Professor Sujay Kaushal of the University of Maryland, geological and hydrological processes naturally bring salts toward the Earth’s surface over time, but human activities such as mining and land use are accelerating the natural “salt cycle.”
Agriculture, construction, water purification and the use of salt to de-ice roads and for other industrial activities intensify salinization.
Agricultural practices, road maintenance and water treatment all contribute to higher salt levels, which can harm biodiversity and, in extreme cases, make drinking water unsafe.
“If the planet is viewed as a living organism, when salt accumulates too much, vital functions and ecosystems can be disrupted. Removing salt from water requires a lot of energy and money, and the resulting brine is often saltier than seawater and difficult to dispose of,” Kaushal noted.
People influence salt concentration
Kaushal and colleagues describe these disruptions as the “anthropogenic salt cycle” and found that humans influence salt concentration and cycling on a global, interconnected scale for the first time.
“Twenty years ago, we only had isolated case studies. Now we can say that surface water in places like New York or drinking water supplies in Baltimore is salty,” said Gene Likens, an ecologist who helped lead the study. Connecticut “Now this is a significant disruption of the entire cycle, from the depths of the Earth to the atmosphere, caused by human activities.”
The study examined a range of salt ions found in both underground and surface waters. Salts are compounds made of positively charged cations and negatively charged anions; among the most abundant are calcium, magnesium, potassium and sulfate ions.
“People often think of salt as sodium chloride, but the research shows a broader set of salts including those related to limestone, gypsum and calcium sulfate have also been altered over the years,” Kaushal explained.
Salt in the air and water
These ions can provoke environmental problems when released in higher doses. The study indicates that human-caused salinization affects areas roughly the size of the United States. Salt ions in streams and rivers have risen over the past five decades, aligning with increased global salt use and production.
Salt can even drift into the air. In some places, lakes are shrinking and salty dust is carried by winds. In snowy regions, road salt can become aerosolized, forming sodium and chloride particles.
Lakes are drying up in some areas, sending salty dust into the atmosphere
Salinization also triggers cascading effects. Salty dust could speed up snowmelt and threaten communities that rely on snowmelt for water. Salt ions can bind to soil pollutants, creating chemical mixtures that persist in the environment and pose risks.
“Salt has a small ionic radius and can squeeze itself between soil particles readily,” Kaushal said. “This is why road salt helps prevent ice crystals from forming.”
Road salt plays a major role in the United States, with about 44 billion pounds used annually for de-icing. Between 2013 and 2017, road salt accounted for 44% of total salt consumption and represented roughly 13.9% of the total dissolved solids entering rivers nationwide. This could lead to higher salt concentrations in river basins, Kaushal warns.
To prevent American waterways from becoming overly saline in the coming decades, the author suggests policies that curb road salt use or promote alternatives.
Reference work: Nature Communications, 2023 edition. (Nature Reviews Earth and Environment)
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The environmental department notes were removed from this article to maintain a focused scientific summary.