Freshwater is getting saltier - with cascading effects worldwide

Freshwater ecosystems, such as rivers, streams, and estuaries, are growing saltier as a result of a combination of natural and human processes.

Several factors are driving this change, threatening the fragile balance of these precious water sources and the species that rely on them.

The growing issue of salinity is addressed in a recent study, which brings to light its long-term impacts on infrastructure, agriculture, and drinking water resources, with economic and environmental implications.

As salinity continues to increase, the need to comprehend, track, and execute mitigation measures becomes more important than ever.

Salinization from both land and sea

Scientists from the University of Maryland have been studying freshwater salinization for years. Their research examines how human activities like road salt use, mining, and land development accelerate the natural “salt cycle.”

But their latest study adds another dimension: the role of ocean saltwater mixing with freshwater supplies, particularly in coastal regions.

“Our paper involves oceanographers for the first time to point out the growing problem of double trouble: salinization from both land and sea,” said study lead author Professor Sujay Kaushal.

“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.”

Hidden costs of saltier freshwater

Salt contamination in freshwater is not just an environmental issue – it has real-world consequences for public health, agriculture, and infrastructure stability.

About 70% of drinking water in the United States comes from rivers and surface water, making it especially vulnerable to rising salinity levels.

Higher salt concentrations make water purification more challenging and expensive, increasing costs for municipalities and households alike.

Farmers also rely on freshwater for irrigation, and increased salinity can damage crops, reduce yields, and degrade soil quality over time. This threatens overall food production.

Infrastructure like bridges, wastewater pipes, and underwater cables can corrode faster due to prolonged exposure to salty water, leading to costly repairs and safety concerns.

Climate change and extreme weather

Salt levels in freshwater can fluctuate due to extreme weather events, making the issue even more unpredictable.

Droughts, floods, and rising temperatures all influence salinity, sometimes worsening the problem by concentrating salts or introducing new sources of contamination.

Researchers warn that climate change, land-based salt pollution, and saltwater intrusion do not act independently but rather interact in complex ways.

Instead, these factors can trigger chemical reactions in water that further amplify contamination, potentially creating toxic byproducts that threaten aquatic life and human health.

Unintended effects of road salt

Study co-author Gene E. Likens explained how road salt, commonly used in winter for safety, can have unintended side effects.

“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,” said Likens.

“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.”

Mitigating threats from saltier freshwater

As salinization intensifies, it is becoming increasingly important to seek effective solutions to protect ecosystems, public health, and economies.

Experts stress the need for ongoing observation of salt levels in freshwater environments and the adoption of preventive measures to avoid future contamination before such damage becomes permanent.

Mitigation of the intensifying threats to water quality and availability could be achieved by dealing with road salt runoff, managing industrial salt discharge, enhancing wastewater treatment, and coastal saltwater intrusion management.

Preventing freshwater salinization

The research offers a useful framework for predicting and preventing freshwater salinization, providing policymakers, environmental authorities, and local communities with direction.

As the world’s temperature rises, precipitation patterns shift, and human activity increases, forward-thinking measures such as sustainable land management and enhanced water conservation strategies are needed to protect vital water resources.

Without immediate action, the world’s rivers, lakes, and drinking water supplies will remain under threat of a saltier and more unpredictable future.

The full study was published in the journal Biogeochemistry.

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