Posted on April 24, 2023
When we first visited Dutch Slough in eastern Contra Costa County last year, the recently restored tidal marsh was already flourishing. But hiding among the reeds was a critical question. How effective would the marsh be at sequestering carbon? A key benefit of restoring wetlands in the age of climate change.
“For doing the inhaling and exhaling, and we’re trying to inhale more carbon dioxide and then exhaling oxygen that we need,” explains University of California biometeorology professor Dennis Baldocchi, Ph.D.
Prof. Baldocchi’s team placed sensitive instruments in the slough to measure greenhouse gases and other data in multiple ways. He says the results after more than a year of monitoring show that the tidal marsh is acting as a powerful carbon sink, drawing CO2 into the ground where it should remain sequestered, instead of contributing to climate change.
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And to compare that benefit, Karen Thorne, Ph.D., and her team from the United States Geological Survey helped take additional measurements. Discovering that while the surrounding farmland is still emitting greenhouse gasses, the new tidal marsh is sequestering CO2 at an even faster rate.
“Our early results are telling us that the Dutch Slough restoration is really pulling in carbon dioxide from the atmosphere 10 times faster than the pasture lands,” says Thorne.
While Dutch Slough is clearly a success story, it didn’t happen overnight. And the work that went into it, could hold lessons for other restoration projects up and down the state. First, the California Department of Water Resources’ plans included excavating the channels and leveling the soil. After that, teams pre-planted some 25,000 Tule plugs along with thousands of trees and shrubs. And finally, after the plants were established, crews broke the surrounding levee, creating the marsh.
“And then the benefits once you have the plants are going to be really big, and they’re going to come really quickly,” says Letitia Grenier, Ph.D., of the San Francisco Estuary Institute.
Grenier has created detailed guides for tidal marsh restoration. She says a key question has been whether the added restoration work is worth the time and effort, compared to less expensive strategies that allow the tidal marshes to form over time.
“So once those plants start growing, if you’ve got the right elevation, you should have a lot of functionality within a year. And then over the years as that wetland matures, and maybe you get more different plant species and a little more diversity coming in, you should get better and better returns, more and more carbon sequestered,” explains Grenier.
And with pressures now ranging from climate change to flooding, to sea level rise, the value of tidal marshes could be critical to California moving forward.
