Will a plankton bloom help bring Delta smelt back from the brink?
The Sacramento-San Joaquin Delta ecosystem was once a very different place.
Before levees and dams, the rivers and streams that flowed through the Central Valley into the San Francisco Bay swelled and shrank with the seasons. Huge, shallow floodplains warmed by the sun mingled with icy mountain snowmelt to create a habitat rich with microscopic plankton, the base of the aquatic food chain.
Now, nearly all the waterways that feed the Delta are channelized for shipping, farming and flood control, none more so than the Sacramento River.
“It’s a deep, cold, dark channel,” said Ted Sommer, a scientist with the Department of Water Resources. “It just doesn’t produce much plankton.”
Sommer is leading an effort to improve conditions for plankton in the hope it will help save from extinction the species that’s most emblematic of the Delta’s ecological woes – the Delta smelt. The tiny fish eat plankton, and smelt numbers are at all-time lows.
“They’re obviously in real trouble right now. A key reason is they’re starving to death,” Sommer said.
Earlier this summer, the state partnered with Sacramento Valley farmers to create a plankton bloom in the Delta that would give the smelt a boost. Agricultural districts in July began pumping 15,000 acre-feet of Sacramento River water into irrigation canals, through the Yolo Bypass and into the north Delta. The state paid $110,000 to offset some of the electrical costs of running the pumps.
Sommer said the idea is to try to mimic the sorts of plankton-friendly conditions that used to exist for longer periods throughout the year in the Sacramento Valley, but that now largely only appear in the winter and spring when the Yolo Bypass floods following heavy storms.
Sommer said he and his colleagues got the idea to try to create a summertime plankton bloom after observing what happened in 2011 and 2012, when farmers had enough water to divert it into the north Delta in autumn.
“We saw the first plankton bloom for fall in 20 years,” he said.
The results from this summer’s experiment so far appear promising, the scientist said. Near the Delta town of Rio Vista, scientists are detecting a noticeable spike in phytoplankton. The microscopic organisms are devoured by zooplankton, the minuscule animals that smelt eat.
It’s still unclear if the bloom will lead to a noticeable increase in smelt numbers. But Sommer said that, regardless, the Delta ecosystem benefits when there’s more plankton to nourish aquatic life.
About $1.6 million has been set aside for smelt food production experiments over three years, said Nancy Vogel, a spokeswoman for the state Natural Resources Agency.
Farmers say they support the plankton program and others that seek to improve Delta fish habitat without cutting back on irrigation water.
“These are the kinds of programs that we ought to be doing as a normal course of business,” said Thad Bettner, general manager of the Glenn-Colusa Irrigation District. The district partnered with the state for the plankton experiment and donated its share of pumping costs.
The plankton experiment is one of several programs outlined in the state’s “Delta Smelt Resiliency Strategy” released in July. The plan’s proposals include allowing more water to flow to the Pacific Ocean, a move that many irrigation districts oppose. Other less-contentious goals include eradicating nonnative aquatic weeds, reducing toxic algae blooms and restoring 5,500 acres of tidal wetlands.
In total, Gov. Jerry Brown’s budget includes $4.2 million for Delta smelt-restoration efforts.
The proposed actions come at a critical time for Delta smelt. In early June, the state Department of Fish and Wildlife released the results of spring surveys that count adult fish. It showed a drop from even the record-low numbers of Delta smelt tallied in last year’s count.