Salt Influx from Land and Sea Spells ‘Double Trouble’ for Drinking Water
New research led by Geology’s Sujay Kaushal reveals that multiple overlapping threats are making fresh water saltier.
An influx of salt from both land and sea and a warming world are condemning the world’s rivers, streams and estuaries to a “saltier future,” according to a new study led by University of Maryland Geology Professor Sujay Kaushal in collaboration with researchers from other institutions.
Published in a special edition of the journal Biogeochemistry, their research tells a comprehensive story of freshwater salinization—rising concentrations of salt ions in bodies of fresh water worldwide—and offers a framework for predicting and preventing the issue.
Researchers strive to find solutions to freshwater salinization because it affects ecosystems and animals adapted to certain salinity levels and can hamper public utilities and food production. Roughly 70% of drinking water in the United States comes from surface waters such as rivers, and higher concentrations of salt can be difficult and costly to remove. Fresh water is also used to irrigate crops and run power plants, and excessively salty waters can corrode infrastructure like wastewater pipes, bridges and underwater cables.
Kaushal has studied land-based sources of salt contamination for more than 20 years and previously led research that found that road salt, mining, land development and other human activities are accelerating the natural “salt cycle,” or the movement of salts to Earth’s surface. In their new study, Kaushal and his co-authors also assessed the threat of saltwater intrusion—the mixing of ocean water with fresh water—of coastal water supplies along tidal rivers.
“Our paper involves oceanographers for the first time to point out the growing problem of double trouble: salinization from both land and sea,” said Kaushal, who holds a joint appointment in UMD’s Earth System Science Interdisciplinary Center. “We now recognize that these salts are coming from two directions and represent an emerging risk that's going to affect a lot of infrastructure, ecosystems, agriculture and drinking water supplies around the world.”
Extreme weather—from droughts to floods to record-high temperatures—can also affect salinity levels for better or worse. Despite this variability, the researchers noted that the effects of climate change, land-based salt pollution and briny ocean water can interact in complex ways, sometimes triggering biogeochemical chain reactions in fresh water that amplify the problem.
Kaushal’s previous research revealed that road salts, widely used to make icy roads and sidewalks safer, have unintended consequences. They often run off into local waterways, mobilizing chemicals that may already be in the water and creating “toxic cocktails.”
Study co-author and Cary Institute of Ecosystem Studies founder Gene E. Likens said their research revealed that the chain reactions don’t stop there.
“What we started realizing is that some of the primary mobilized chemical cocktails react with other contaminants to form secondary chemical cocktails, packing a one-two punch to water quality,” Likens said. “What’s concerning is that these chain reactions are happening all along the freshwater-marine continuum now with cascading effects on ecosystems, agriculture and infrastructure.”
In one example, the researchers found that tidal fresh waters of the Patuxent River, a tributary of the Chesapeake Bay, contain particularly high concentrations of road salts. “Strong pulses” of salt ions are particularly apparent in the winter months when salt-laced solutions are used to treat icy roads.
“In some places, the road salt and the pollution from the urban areas goes far downstream into the tidal areas,” Kaushal said. “We never expected to trace these pulses of road salt from land to tidal waters or that these pulses could impact intakes for drinking water, power plants and agriculture.”
Though the Washington, D.C. region has experienced fewer snow days over the last century, it has also had more intense snowfalls over shorter time periods in recent decades. The researchers noted that urban development and continued reliance on road salts has led to increasingly severe salinity spikes in many local streams and rivers, including the Potomac.
“People are tempted to say that this problem has gone away with a warming climate, but we found that this isn’t true and that salinity pulses can be amplified by weather extremes,” Kaushal said. “I think a big contribution of our paper is recognizing the role of climate variability and how that can increase salt coming from pollution on land as well as saltwater intrusion.”
Kaushal explained that salinization can be an added stressor for waterways that are already experiencing issues like eutrophication—an overload of nutrients that can trigger harmful algal blooms, which can deplete oxygen in the water and hurt fish and other aquatic animals. Kaushal and his co-authors noted that more research is needed to predict how climate change will affect the spread and severity of these types of chain reactions along streams, rivers and tidal waters.
Despite the unknowns, Kaushal said many of the effects of salinization can be predicted and prevented. His team’s latest research proposes a risk management framework designed to pinpoint where and when salinization might occur along a particular waterway.
“There's no comprehensive guidance document that explains all the risks and where they would occur from fresh water to marine water, so I think our paper is a first step in that direction,” Kaushal said. “Even though we have shown that there are global changes in salinization, each river or estuary has its own set of unique risks, so our framework can help anticipate emerging risks faced by headwater streams all the way down to tidal waters that will affect our water, energy sources and food.”
Kaushal hopes their framework will be used by those who oversee rivers, estuaries and drinking water supplies because freshwater salinization is an issue that affects fundamental human needs like drinking water.
“We don’t have plans to deal with salt,” Kaushal said. “Regional salinity management plans and guidance documents and risk assessments for rivers around the world that are based on our framework—that's what I’d like to see come out of our study.”
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In addition to Kaushal, other UMD-affiliated co-authors included geology majors Daniel Collison and Kyriaki Papageorgiou, geology Ph.D. student Sydney Shelton, environmental science and technology graduate student Jazmin Escobar (B.S. ’23, environmental science and policy), Bennett Kellmayer (B.S. ’23, geology), Joseph Malin (B.S. ’21, M.S. ’23, geology), Ashley Mon (B.S. ’24, biochemistry), Jenna Reimer (B.S. ’19, geology) and Ruth Shatkay (B.S. ’19, architecture; M.S ’21, environmental science and technology).
Their paper, “Freshwater Faces a Warmer and Saltier Future from Headwaters to Coasts: Climate Risks, Saltwater Intrusion, and Biogeochemical Chain Reactions,” was published in Biogeochemistry on March 10, 2025.
