科学美国人60秒:Desalination Could Cause Ecological Sea Change

Winter storms have walloped California this year, and snowpack is piling up. But just a few years back, the state was wrung dry by a record-breaking drought. And more dry spells will surely come. 

"I think everybody agrees that we need more water resources." Adina Paytan, an oceanographer at the University of California, Santa Cruz. She points out that her home country, Israel, faced the same problem. "Israel had water issues for ever and ever. They don't have water issues anymore because they converted pretty much 90 percent of water use to desalination.”

Ocean desalination hasn't enjoyed as much traction in California due to its cost, and because of concerns that the plants would damage coastal ecosystems—both when seawater is sucked in, and when leftover super-salty brines are released. Now, writing in the journal Water, Paytan and her team have assessed the environmental impact of the nation's largest plant: the Carlsbad Desalination Plant, north of San Diego. [Karen Lykkebo Petersen et al., Biological and Physical Effects of Brine Discharge from the Carlsbad Desalination Plant and Implications for Future Desalination Plant Constructions]

Here's the good news. Scuba dives revealed that the communities of starfish, snails, sea cucumbers and other creatures that live on the sandy ocean bottom offshore have not budged since the plant opened in 2015. But the bad news? The plume of salty runoff stayed intact much farther out than models predicted, rather than easily blending with closer seawater.

"When you have a pool of salty water that doesn't mix, it prevents oxygen from penetrating, so it can cause lower oxygen levels close to the bottom and obviously, all the organisms that need oxygen are not going to be happy."

Ecosystems offshore from the Carlsbad plant were already disturbed by cooling water discharge from a power plant at the same site, she says, which could explain why the marine life was unfazed. But at more pristine sites, especially those rich in biodiversity like kelp forests, a salty plume might do more harm. 

The state's already planning more ocean desalination projects up and down the coast. Paytan says her lesson is this: "There's tons of water in the ocean. We can use it but we just have to do it responsibly." First step: updating our models of how salty wastewater behaves offshore. To ensure that our thirst for drinking water doesn't cause an ecological sea change.

—Christopher Intagliata