Dead fish at Salton Sea, 2010
PHOTO: Céline Pallud

New Wetland Design a Leap Forward in Cleansing Toxins From Salton Sea

A rotten-egg stench that fouled a swath of Southern California last fall was traced to the Salton Sea — the latest episode in the environmental woes of California’s largest, but rapidly shrinking, inland lake. Now a study has demonstrated a cost-effective method for using manmade wetlands to clean contaminants from the freshwater rivers that flow into the sea, which is overly salty from evaporation and polluted with selenium, fertilizer nutrients, and other chemicals from agricultural runoff.

The study found that a new wetland design reduced selenium in the water column to previously unachieved low levels — less than 1 part per billion. “The only other way to get water this clean is to use microbial bioreactors, which are prohibitively expensive and not feasible on the vast scale of the Salton Sea,” said Norman Terry, a UC Berkeley professor of plant and microbial biology and principal investigator for the study.

In the proposed multistep process, water from the Alamo River or New River would be pumped into a sedimentation pond, then allowed to flow through an algae pond and into a constructed wetland growing cattail plants before finally entering a species conservation habitat area.

The algae are extremely efficient in removing and gasifying the selenium, completely eliminating it from the ecosystem, Terry said. In addition, researchers say, the algae, which contain as much as 50 percent oil, could be harvested and sold for biofuel, providing a potential source of income for the restoration project.

The study, published in the November 6 issue of Environmental Science and Technology, was funded as part of efforts by the California Department of Fish and Wildlife and Department of Water Resources to develop pilot restoration projects that provide feeding habitat for more than 400 species of resident and migratory birds threatened by the sea’s deteriorating environmental conditions.

“If a pilot wetland is successful in supplying clean water to support the species conservation habitat, this cost-effective process could be applied to the Salton Sea itself, and to other sensitive environments,” Terry said. “For example, it could be used to clean up irrigation drainage water for reuse in agriculture, reducing the billions of gallons of water that are lost to the atmosphere in evaporation ponds.”

“You might call it a down payment. If we can prove this design is an effective way to get the water clean enough to restore these natural environments, then the technology has the potential to solve many of California’s water problems.”

SEA CREATURES: Fast-working microorganisms immobilize selenium that reaches the Salton Sea by quickly transforming it from a water-soluble form to a solid form, which is then sequestered in the sediment, according to research by Juan Fernando Villa-Romero, a graduate student in the lab of Céline Pallud, an assistant professor of environmental science, policy, and management. The finding indicates this natural biological process results in almost complete selenium removal from Salton Sea water. The study was published in the January 2013 issue of Hydrobiologia.