Why is dumping seawater on fires not the solution to California’s wildfire problem?

Our coastal forests have shown little impact since their first 10-hour exposure to salt water in June 2022, and have grown normally for the rest of the year. We increased the exposure to 20 hours in June 2023, and the forest remained mostly undisturbed, although… Tulip poplar trees They were pulling water from the soil more slowly, which could be an early warning sign.

Things changed after a 30-hour exposure in June 2024. The leaves of tulip poplars in the forests began turning brown in mid-August, several weeks earlier than normal. By mid-September, the forest canopy was bare, as if winter had arrived. These changes did not occur on a nearby plot of land that we treated in the same way, but with fresh water rather than seawater.

The initial resilience of our forests can be partly explained by the relatively low amount of salt in the waters of this estuary, where water from freshwater rivers mixes with salty ocean water. The rains that fell after the experiments in 2022 and 2023 washed away the salts from the soil.

But a major drought occurred after the 2024 experiment, so the salts remained in the soil at that time. Longer exposure of trees to salty soil after our 2024 experiment may have exceeded their ability to withstand these conditions.

The seawater dumped in the Southern California fires is full-strength salty ocean water. And the conditions there It was very dryespecially compared to our East Coast forest plot.

Changes are evident in the land

Our research group is still trying to understand all the factors that limit a forest’s tolerance to saltwater, and how our findings apply to other ecosystems like those in the Los Angeles area.

The tree leaves turning from green to brown before fall was a surprise, but there were other surprises hidden in the soil beneath our feet.

Rainwater seeping through the soil is usually clear, but about a month after the first exposure to saltwater for just 10 hours in 2022, the soil water turned brown and stayed that way for two years. The brown color comes from carbon compounds leached from dead plant material. It is a similar process to making tea.

Water extracted from the soil after a saltwater experiment is the color of tea, reflecting the abundant compounds leached from dead plant material. Normally, the soil water will appear clear.

Photograph: Alice Stearns/Smithsonian Environmental Research Center, CC BY-ND