Salt contamination of freshwater supplies continues to be a major problem around the world, threatening the safe drinking water of billions of people. Roughly 70% of the U.S. drinking water supply comes from surface waters, including the tidal fresh regions of estuaries. Drought and sea-level rise, which lead to saltwater intrusion from the ocean, and changes in land use, which lead to freshwater salinization, are putting water resources at risk. According to the U.S. Environmental Protection Agency, human activities such as road salt application, water softening, mining and oil production, commercial and industrial processes, weathering of concrete and fertilizer application are also to blame.
A number of aquatic processes may affect salt intrusion into estuaries and tidal rivers, including sea-level rise, changing ocean circulation, changing tides, wind events and dredging of navigation channels. However, understanding how these processes work in concert with extended drought to drive extreme salt intrusion under climate change remains a mystery; this gap in scientific understanding has been exposed in a number of news reports. One of the issues identified is the lack of international effort to synthesize the regionally distributed scientific findings on this topic, in addition to a lack of identified priorities for future research.
To that end, the Scientific Committee on Oceanic Research (SCOR) has granted funding to a working group proposal on oceanic salt intrusion into tidal freshwater rivers. The working group, led by Ming Li, a professor at the University of Maryland Center for Environmental Science (UMCES), and Hans Burchard, a professor at Leibniz Institute for Baltic Sea Research, will synthesize research on saltwater intrusion over a period of four years beginning in early 2025. The goal of the team – made up of 21 scientists from 18 countries – is to develop a global synthesis of this emerging topic, discern the roles of global climate change and local oceanic processes, and develop tools for observing, modeling and analyzing salt intrusion into tidal rivers.
"The World Health Organization recommends that drinking water not contain more than 250 mg/L of chloride, and high sodium levels (>20 mg/L) in drinking water are linked to hypertensive disorders and developmental delays in children," said Li. "Since seawater contains about 19,400 mg/L of chloride and 10,670 mg/L of sodium, saltwater intrusion poses a major threat to public health."
Indeed, salt contamination of drinking water intakes in tidal rivers has made headline news worldwide in recent years. The U.S. Army Corps of Engineers, for example, had to barge fresh water to water treatment facilities in New Orleans to dilute the salinity content to levels safe for drinking in the fall of 2023. Salt intrusion also occurred in the Changjiang River in 2022, contaminating drinking water supplies and leading to panic-driven stockpiling of bottled water in Shanghai. The 2022 drought in Europe led to strong salt intrusion of the Rhine River and triggered emergency water conservation measures in The Netherlands.
The working group – having expertise in fields such as estuarine physics, coastal oceanography, ocean observations and data analysis, and numerical ocean modeling – aims to develop a better scientific foundation to inform strategies to mitigate this alarming and pervasive problem.
Additional team members include Julie Pietrzak (Delft University of Technology, Netherlands), Nadia Pinardi (University of Bologna, Italy), Isabel Jalon Rojas (Bordeaux University, France), Yuley Cardona (Universidad Nacional, Colombia), Megan Williams (Pontificia Universidad Católica, Chile), Rich Pawlowicz (University of British Columbia, Canada), Antonio M. Hoguane (Eduardo Mondlane University, Mozambique), Wenping Gong (Sun Yatsen University, China), John Largier (University of California, Davis, USA), Arnoldo Valle Levinson (University of Florida, USA), Ruth Musgrave (Dalhousie University, Canada), Debora Bellafiore (National Research Council – Institute of Marine Sciences, Italy), Manuel Diez Minguito (University of Granada, Spain), Carlos Augusto Schettini (Universidade Federal do Rio Grande, Brazil), Rosario Sanay (Universidad Veracruzana, Mexico), Gisselle Guerra (Universidad Tecnologica de Panama), Charitha Pattiaractchi (University of Western Australia), Hui Wu (East China Normal University, China), and Shinichiro Kida (Kyushu University, Japan).
