After years of searching high and low for a culprit in the collapse of Delta fish populations, scientists are learning the problem may lie right under their noses.
The likely fish killer is ammonia, a common byproduct of human urine and feces.
Sacramento's regional sewage treatment plant is the largest single source of ammonia in the Delta. It discharges treated wastewater from nearly 1.4 million people into the Sacramento River near Freeport – without removing ammonia.
Two recent studies by Richard Dugdale, an oceanographer at San Francisco State University, show that ammonia disrupts the food chain in the Sacramento-San Joaquin Delta.
The discovery, if it holds up to further scientific review, reveals how just one factor can tilt the Delta's complex ecological balance. It also illustrates how fixing the Delta will be a costly task for many California residents who mistakenly assume their lives are not connected to the estuary.
The Sacramento Regional County Sanitation District estimates it needs as much as $1 billion to remove ammonia from the metro area's wastewater. Monthly sewer bills would have to triple throughout the region.
"We're not going out on the edge to say this is the whole answer," said Dugdale, co-author of the studies along with others at the university's Romberg Tiburon marine lab. "But we think it's part of the reason for the decline in (ecological) productivity."
Ammonia in the river does not make fish unsafe to eat, nor does it pose a threat to recreation. It does, however, seem to interrupt a natural food production line that would otherwise yield abundant blooms of tiny aquatic animals to feed salmon, smelt and bass, Dugdale said.
Those species have been in steady decline.
The ammonia threat was dramatically illustrated last May when dozens of chinook salmon showed up dead in the San Joaquin River near Stockton's sewage outfall. Anke Mueller-Solger, an environmental scientist at the state Department of Water Resources, said the fish may have been killed by high levels of ammonia in the wastewater.
Sacramento's effluent problem is slightly different. Rather than high concentrations of ammonia, the threat is the enormous volume of ammonia-laced wastewater. The regional sewer agency treats human waste from Sacramento, West Sacramento, Folsom, Carmichael, Rancho Cordova, Elk Grove and other unincorporated communities.
The plant near Freeport each day releases about 146 million gallons of treated wastewater into the Sacramento River. That's enough to fill about 225 Olympic-size swimming pools daily.
Despite this volume, Mueller-Solger said, the Sacramento River is traditionally considered the Delta's lifeblood, because it provides the vast majority of fresh water entering the estuary.
"But there is this big urban area called Sacramento and it's been growing like gangbusters," she said. "Obviously, sewage is produced proportionally to the number of people, so the water's perhaps not quite as nice and clean as we thought."
The ammonia load in Sacramento's wastewater has more than doubled since 1985 due to rapid urbanization, and is now more than 125,000 gallons per month. That's 10 times more than the Stockton sewage plant.
To handle more growth, the regional sewer agency is planning a major expansion that would allow total discharge volume to grow 30 percent. The plan includes no ammonia controls.
"This is a cost of growth that is too often externalized onto a degraded environment," said Bill Jennings, executive director of the California Sportfishing Protection Alliance and longtime Delta water-quality watchdog.
Jennings called it "simply reprehensible" that the sewer agency hasn't already improved its systems to remove ammonia and other contaminants.
Sewage officials counter that they have a responsibility to ratepayers. They estimate upgrading the wastewater treatment plant to filter out ammonia would cost $740 million. To remove excessive nitrates produced as a byproduct of that treatment would raise the cost to $1 billion.
Call The Bee's Matt Weiser, (916) 321-1264.
