In spring 2015 the California Department of Water Resources dropped 150,000 tons of rock into False River in the Central Delta to halt encroaching tides that had little freshwater to hold them back. A few months later, it was clear the barrier worked, as salinity rose on one side and fell on the other. But what were the effects on local plants and animals? Through six overlapping yet distinct projects funded by the state Delta Science Program and NASA, and described in the September 2019 issue of San Francisco Estuary and Watershed Science, researchers studied impacts on water quality and movement, zooplankton and phytoplankton, submerged aquatic vegetation, nutrients, and two species of clam. What they found, says Wim Kimmerer of the Estuary & Ocean Science Center at San Francisco State University, who co-authored the new synthesis of the work, was that not all that much happened. “The barrier didn’t really do that much in terms of the things we were expecting, with the exception of some shifts in aquatic vegetation.” Typically, the water body to the east of the barrier, a sunken island called Franks Tract, is partially full of a mix of native and invasive plants such as  Brazilian waterweed. With the barrier in place, reduced flows through the center of the tract allowed aquatic vegetation to claim more territory. But other outcomes were either ambiguous or “ecologically unimportant,” Kimmerer says. The barrier was painstakingly removed in the fall, but a year later, aerial imagery showed that Franks Tract was still choked with plants, Kimmerer said. It may take time for the tidal injection through False River to clear out the channel again—unless another drought and a new barrier return first.

 

Pearls in the ocean of information that our reporters didn’t want you to miss
 

An emergency barrier installed to protect the state’s water supply from saltwater intrusion during the recent record-setting drought had little effect on the ecosystem.

In spring 2015 the California Department of Water Resources dropped 150,000 tons of rock into False River in the Central Delta to halt encroaching tides that had little freshwater to hold them back. A few months later, it was clear the barrier worked, as salinity rose on one side and fell on the other. But what were the effects on local plants and animals? Through six overlapping yet distinct projects funded by the state Delta Science Program and NASA, and described in the September 2019 issue of San Francisco Estuary and Watershed Science, researchers studied impacts on water quality and movement, zooplankton and phytoplankton, submerged aquatic vegetation, nutrients, and two species of clam. What they found, says Wim Kimmerer of the Estuary & Ocean Science Center at San Francisco State University, who co-authored the new synthesis of the work, was that not all that much happened. “The barrier didn’t really do that much in terms of the things we were expecting, with the exception of some shifts in aquatic vegetation.” Typically, the water body to the east of the barrier, a sunken island called Franks Tract, is partially full of a mix of native and invasive plants such as  Brazilian waterweed. With the barrier in place, reduced flows through the center of the tract allowed aquatic vegetation to claim more territory. But other outcomes were either ambiguous or “ecologically unimportant,” Kimmerer says. The barrier was painstakingly removed in the fall, but a year later, aerial imagery showed that Franks Tract was still choked with plants, Kimmerer said. It may take time for the tidal injection through False River to clear out the channel again—unless another drought and a new barrier return first.

 

About the author

Nate Seltenrich is a freelance science and environmental journalist who covers infrastructure, restoration, and related topics for Estuary. He also contributes to the San Francisco Chronicle, Sonoma and Marin magazines, the journal Environmental Health Perspectives, and other local and national publications, on subjects ranging from public lands and renewable energy to the human health impacts of climate change. He lives in Petaluma with his wife, two boys, and four ducks. www.nate-reports.com

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