ÌÇÐÄÊÓƵ

A new paper in Environmental Science & Technology Letters warns of an emerging global threat posed by salt contamination of water supplies in tidal rivers worldwide. The paper, co-authored by David Ralston, Department Chair in the Applied Ocean ÌÇÐÄÊÓƵics & Engineering Department in the Woods Hole Oceanographic Institution, along with an international team of partner institutions, highlights how a combination of climate change impacts—including prolonged drought and rapid sea-level rise—along with localized human activities, are intensifying the increase in salt in vital freshwater sources.

"This subject is a great example of how basic research on ocean and watershed processes affecting the salinity in estuaries and tidal rivers can help us manage the public health and economic risks from changing environmental conditions," said Ralston.

Nationally, more than $1 trillion in infrastructure investments are needed in drinking and wastewater systems, and in the Mid-Atlantic alone, nearly $100 million in agricultural activity is at risk. Beyond agricultural irrigation, salt contamination poses a substantial threat to industrial production and critical infrastructure through corrosion, compromising power plant cooling systems, water treatment plants, bridges, and other vital components.

Surface waters, including tidal rivers, provide approximately two-thirds of the global drinking water supply, and tidal rivers are increasingly vulnerable to saltwater intrusion. The paper synthesizes studies from around the world, detailing instances where drinking water intakes have been threatened in major rivers such as the Mississippi, the Delaware, and the Hudson in the United States, as well as global examples including the Changjiang in China, the Chao Phraya in Thailand, and the Rhine in Europe, among many others.

"Salt contamination of water supplies in tidal rivers is a global problem but has received little attention beyond site-specific studies," Dr. Li said. The research highlights oceanic and hydrologic processes that drive saltwater intrusion, as well as watershed processes that lead to enhanced chemical weathering and the export of salts into rivers.

Key findings from the study:

• Climate change as a major driver: Accelerated relative sea-level rise, altered drought and river flow, and extreme weather events are significantly increasing saltwater intrusion.
• Human impacts: Local human activities, such as channel deepening in estuaries, excessive use of salt on roadways, and other human-accelerated chemical weathering in watersheds, have historically contributed to and continue to exacerbate salinity issues.
• Widespread impact: Saltwater intrusion is affecting rivers across all continents, impacting diverse regions from semi-arid climates to precipitation-rich temperate zones, and causing damage to infrastructure.
• Broader consequences: Freshwater salinization can lead to secondary effects, including the exacerbation of hypoxia and the mobilization of contaminants such as nutrients, metals, and radionuclides, which further stress water systems and their associated infrastructure.

In the United States, there isn't a federal drinking water standard for salinity. This critical research underscores the urgent need to bring together scientists, engineers, water resource managers, and lawmakers to protect freshwater supplies and the vital infrastructure that delivers them from the escalating threat of salt contamination. Recommendations include:

• Ion-specific measurements: Enhanced monitoring and measurement of major salt ions are crucial to better understand their sources, transport, and fate in watersheds and tidal rivers, aiding in the protection of infrastructure.
• Ion-specific hydrologic-hydrodynamic models: Developing models that can simulate the transport of individual salt ions is essential for accurate prediction and for assessing risks to infrastructure.
• Human-centered decision support tools: The development of decision support tools for predicting and managing salt contamination should involve stakeholders through a human-centered design approach, ensuring that infrastructure resilience is a key consideration.