Using Seawater to Combat LA Fires is an Experiment Scientists are Monitoring Closely

Firefighters tackling the devastating wildfires that swept through the Los Angeles area in January 2025 faced challenges due to limited freshwater supplies.

When conditions allow, experienced pilots operating aircraft known as Super Scoopers collect 1,500 gallons of seawater at a time, delivering it with pinpoint accuracy to combat the flames.

Using seawater to fight fires may seem like a straightforward solution, given the vast supply provided by the Pacific Ocean. In emergencies like those in Southern California, it’s often the fastest option, although navigating ocean swells can make the operation risky.

However, seawater comes with drawbacks.

Impact of Saltwater on Firefighting Equipment and Ecosystems

Saltwater can corrode firefighting equipment and potentially harm ecosystems, particularly in areas like Los Angeles’ chaparral shrublands, which are not accustomed to salt exposure. While small amounts of salt—such as those found in fertilizers—are generally harmless to plants, excessive salt can cause stress or even death.

Although the long-term impact of seawater on ecosystems remains uncertain, we can draw parallels by examining the effects of sea-level rise to anticipate potential consequences.

As an ecosystem ecologist at the Smithsonian Environmental Research Center, I lead a groundbreaking experiment called TEMPEST, designed to explore how and why historically salt-free coastal forests respond to their first encounters with saltwater.

Over the past century, global sea levels have risen by an average of about 8 inches, driving salty water into forests, farmlands, and neighborhoods that were previously sustained by freshwater.

Sea-Level Rise and the Formation of Ghost Forests

With the pace of sea-level rise accelerating, storms are carrying seawater further inland, ultimately killing trees and transforming once-thriving areas into ghost forests—a visible and widespread consequence of climate change both in the U.S. and around the world.

In our TEMPEST test plots, we draw salty water from the nearby Chesapeake Bay into tanks and then distribute it over the forest soil surface, saturating it for approximately 10 hours. This process replicates the effects of a storm surge bringing salty water onto the land.

Saltwater Exposure and Its Impact on Coastal Forests

During the initial 10-hour exposure to salty water in June 2022, our coastal forest showed minimal impact and continued to grow normally for the rest of the year. When we extended the exposure to 20 hours in June 2023, the forest still seemed largely unaffected, though tulip poplar trees began absorbing soil water more slowly—a potential early warning sign.

After a 30-hour saltwater exposure in June 2024, tulip poplar leaves began browning by mid-August—weeks earlier than usual. By mid-September, the forest canopy was bare, resembling winter. A nearby freshwater-treated plot showed no such changes.

Initially, our forest’s resilience stemmed from the estuary’s relatively low salt levels and rainfall in 2022 and 2023, which flushed salts from the soil. However, a drought after the 2024 experiment left salts lingering, pushing the trees beyond their tolerance.

In contrast, seawater used on Southern California fires is much saltier, with drier conditions than those in our East Coast forest study.

Our research team is working to uncover the various factors that influence the forest’s ability to withstand salty water and explore how these findings might relate to ecosystems like those in the Los Angeles region.

Unexpected Effects of Saltwater on Soil and Tree Health

The early browning of tree leaves ahead of autumn was unexpected, but the soil beneath held even more surprises. Normally, rainwater filtering through the soil is clear. However, about a month after the initial 10-hour salty water exposure in 2022, the soil water turned brown and remained that way for two years. This discoloration resulted from carbon-based compounds leaching out of decaying plant matter—a process much like brewing tea.

Laboratory tests indicate that salt caused clay and other particles in the soil to disperse and shift. These alterations in soil chemistry and structure can endure for years.

Although ocean water can aid in fighting fires, fire officials typically prefer freshwater sources—assuming they are available. Meanwhile, US coastlines are experiencing more frequent and widespread saltwater exposure as rising global temperatures drive sea-level rise, flooding forests, fields, and farms, with uncertain consequences for coastal ecosystems.

Read the original article on: Science Alert

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