Our coastal forest showed little effect from the first 10 hours of 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 seemed virtually undisturbed, although the tulip poplars They were extracting water from the ground more slowly, which may be an early warning sign.
Things changed after a 30-hour exposure in June 2024. The leaves of forest tulip poplars began to 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 in a nearby plot that we treated in the same way, but with fresh water instead of seawater.
The initial resilience of our forest can be explained in part by the relatively low amount of salt in the water of this estuary, where water from freshwater rivers and the salty ocean mix. The rain that fell after the experiments in 2022 and 2023 washed away the salts in the soil.
But the 2024 experiment was followed by a major drought, so the salts remained in the ground at that time. The trees’ longer exposure to salty soils after our 2024 experiment may have exceeded their ability to tolerate these conditions.
The seawater dumped on the Southern California fires is pure, salty seawater. And the conditions there they have been very dryparticularly in comparison to our east coast forest plot.
Obvious changes in the terrain
Our research group is still trying to understand all the factors that limit forest tolerance to salt water and how our results apply to other ecosystems such as those in the Los Angeles area.
The leaves on the trees turning from green to brown long before fall was a surprise, but there were other surprises hidden in the ground beneath our feet.
Rainwater seeping through the ground is normally clear, but about a month after the first and only 10-hour exposure to salt water in 2022, the water in the ground turned brown and stayed that way for two years. The brown color comes from carbon-based compounds leached from dead plant material. It is a process similar to making tea.