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Our coastal forest showed little effect from the first 10-hour exposure to salt water 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 appeared largely undisturbed, although the poplar tulips they draw water from the ground more slowly, which can be an early warning sign.
Things changed after a 30-hour exposure in June 2024. Tulip poplar leaves in the woods began to turn brown in mid-August, several weeks earlier than normal. In mid-September, the forest canopy was bare, as if winter had settled. These changes did not occur in a nearby plot that we treated in the same way, but with fresh water instead of sea water.
The initial resilience of our forest can be explained in part by the relatively low amount of salt in the water in this estuary, where water from freshwater rivers and a salty ocean mix. The rain that fell after the experiments in 2022 and 2023 washed the salts from the ground.
But a major drought followed the 2024 experiment, so the salts were in the ground then. The longer exposure of trees to saline soils after our 2024 experiment may have exceeded their ability to tolerate these conditions.
The seawater that is dumped on the volcanoes of Southern California is full strength salty ocean water. The conditions here they were very dryparticularly compared to our East Coast forest plot.
Obvious changes in the land
Our research group is still trying to understand all the factors that limit the forest’s tolerance to salt water, and how our results apply to other ecosystems such as those in the Los Angeles area.
Tree leaves turning from green to brown well before autumn was a surprise, but there were other surprises hidden in the ground under our feet.
The rainwater that seeps into the ground is normally clear, but about a month after the first and only 10 hours of exposure to salt water in 2022, the ground water turned brown and remained so for two years The brown color comes from carbon-based compounds leached from dead plant material. It is a similar process to making tea.
