Our riparian forest showed little effect from the first 10-hour saltwater exposure in June 2022 and grew normally for the rest of the year. We increased the exposure to 20 hours in June 2023, and the forest still looked mostly dormant, although the cypress trees drew water from the soil more slowly, which may have been an early warning signal.
Everything changed after a 30-hour exposure in June 2024. Tulip fir leaves in the woods started turning brown a few weeks earlier than usual in mid-August. By mid-September, the forest canopy was bare, as if winter had begun. These changes did not occur in a nearby fragment that we were dealing with, but with freshwater rather than seawater.
The early resilience of our forest can be explained in part by the relatively low salt content of the water in this estuary, where freshwater rivers and brackish oceans mix. The rain that fell after the tests in 2022 and 2023 washed the salts out of the soil.
But after the 2024 experiment there was a major drought, so the salts remained in the soil. Longer exposure of trees to saline soils after our 2024 experiment may have exceeded their ability to tolerate these conditions.
The seawater being dumped on the Southern California wildfires is full-strength, salty ocean water. And conditions there have been very dry, especially compared to our East Coast forest patch.
Visible changes on the ground
Our research group is still trying to understand all the factors that limit forest tolerance to saltwater and how our results apply to other ecosystems like those in the Los Angeles area.
The leaves of the trees turning from green to brown before autumn was amazing, but there were other wonders hidden in the soil under our feet.
Rainwater that infiltrates the soil is normally clear, but about a month after the first and only 10 hours of exposure to salt water in 2022, the soil water turned brown and remained that way for two years. The brown color is from carbon-based compounds leached from dead plant matter. This process is similar to making tea.
