California's sinking delta
Efforts are under way to reverse the deterioration of a major water source, the Sacramento-San Joaquin Delta in California, which is sinking.
Dennis Baldocchi often drives past the ruins of his grandmother’s house on Sherman Island, in northern California’s Sacramento-San Joaquin River Delta. Flooding gutted the house when the island’s levee broke 40 years ago. Today, grass grows through the floors and chickens wander through.Skip to next paragraph
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To Dr. Baldocchi, the slanting hulk whispers an unsettling truth: The land that his family farmed for three generations is sinking farther below sea level each year.
Immigrants began arriving at the Sacramento River Delta 150 years ago. They drained 450,000 acres of marshy lands so that they could farm asparagus, corn, and sugar beets.
Their ingenuity fueled an economic boom, but it also triggered a slow-motion catastrophe: Draining allowed oxygen to penetrate the soil, permitting microbes to consume organic detritus that had lain undisturbed for millenniums, and to churn out carbon dioxide. As the soil deflated, the land sank as much as two inches per year.
Baldocchi, now a biogeochemist at the University of California in nearby Berkeley, spent much of his childhood on Sherman Island, pheasant hunting and helping harvest asparagus on his uncles’ farms. He didn’t appreciate the slow changes that were taking place in the land until he returned in 1999, after 22 years away.
Baldocchi motions to the road ahead. It hovers six feet above the plowed fields. The roads have sunk more slowly than surrounding fields, since blacktop slows the seepage of oxygen, which microbes need to devour peat. “When you grow up here, an inch or two per year you don’t notice,” he says. “But if you’re gone 22 years and it drops two or three feet, you get a visual sense of it.”
Land that once stood at sea level now lies as much as 20 feet below. The delta has exhaled 2 billion tons of carbon dioxide – greater than California’s total annual carbon emissions.
The sinking continues, with no end in sight. “They’ve lost already maybe [five] meters,” says Baldocchi.
A study by Steven Deverell, a hydrologist at HydroFocus in Davis, Calif., predicts that by 2050, some islands in the delta could drop another four feet.
Stepping onto a field, Baldocchi inserts a posthole digger into the ground. Three feet down, he reaches soil that has never felt a plow. He rises with a handful of brown peat that’s speckled with the woody fragments of tule reeds. “This is 4,000 years old,” he says. But within decades those aged tule stalks will evaporate back into the atmosphere, if current conditions continue.
Baldocchi’s gas-sniffing instruments on Sherman Island show that each square meter of pasture loses about 2/10ths of a gram of carbon per day. It sounds small – until you realize that across the entire delta 20,000 cubic meters of peat disappear each day.