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Breathtaking Ship Channel Stumps Scientists
Anyone with an ounce of salmon savvy can tell you that the biggest obstacles lurking in the migration path of anadromous fish are high dams and hard-sucking water pumps. But there's one major obstacle on their San Joaquin River route that's less obvious to the naked eye: a 15-mile stretch of dark deep water off Stockton just short enough of oxygen to make fall-run salmon turn tail.
"CALFED's worried because they're spending millions laying salmon spawning gravels upstream, but what if the moms can't get to the maternity ward," says the Central Valley Regional Water Quality Control Board's Chris Foe. In years past, dissolved oxygen levels as low as 1.5-2 milligrams per liter have been measured in the Stockton Deepwater Ship Channel, much lower than the Board's water quality objectives of 5-6 milligrams per liter (the objective varies with the month).
The culprit, in this dissolved oxygen-deficiency-mystery, isn't a nasty sewage outfall or irrigation pipe, nor a by-product of human tinkering with river flows and depths, nor nature out of synch, it's all of the above and more - or at least that's what scientists think. In the next year a team of 15 technical experts, each hired by different stakeholder interests, will be managing an $866,000 CALFED-funded investigation of the causes of the problem to help stakeholders and regulators decide who should ultimately be held accountable, and what can be done to reoxygenate the ship channel.
"There's no one problem, no smoking gun," says BurRec's Doug Ball, who sits on the technical committee.
The scientific basics are these: under normal river depths algae and phytoplankton move around in the water column enough to get enough sunlight to photosynthesize, and thus produce oxygen. The amount of algae and phytoplankton in the San Joaquin River, meanwhile, is fairly high due to the quantity of nutrients flowing into the river upstream from cities and farms - nutrients fuel algae growth.
When the 10-foot-deep river suddenly hits the 35-foot-deep dredged ship channel, the water slows down and less mixing occurs. Algae and other organic material sits around in the deeper darker water and down in the bottom sediments much longer, and without light only consume but don't produce oxygen. More oxygen is consumed by organisms in the sediments and other channel bottom processes, meanwhile (see chart). All this oxygen demand is exacerbated by the low (or even reverse) flow conditions that often occur due to the way water exports are managed - the Old River cutoff to the export pumps is only 10 miles upstream of Stockton.
"Generally during the fall there's little or no net flushing in the channel, and the water is just getting sloshed back and forth with the tides," says the U.S. Geological Survey's Rick Oltmann. "We need to better understand how the depth and geography of the channel contribute to negative oxygen production," says state Water Resources' Peggy Lehman, who is heading up the investigation.
Investigators clearly have their work cut out for them. The system is so full of different kinds of algae, other organic matter and growth-spurring nutrients, all deriving from diverse municipal, agricultural and natural sources up and down the river, that it's difficult to pinpoint exactly which algae goes where and does what - in terms of consuming or producing oxygen - in the river. "The key is trying to identify the ultimate source of the material creating the problem," says Lehman.
Preparatory research done last year provided two leads, suggesting that upstream sources may be more important that anyone anticipated, and that sediment oxygen demand may be less so - a conclusion that surprised many members of the technical committee. About 60,000-70,00 pounds of BOD (biological oxygen demand)-causing constituents flow into the deepwater channel from upstream each day, as opposed to an estimated 6,000 pounds coming from channel sediments, according to consultant Fred Lee, who is compiling the preliminary data in an issue paper.
Delving deeper into the upstream contribution will require a look at all inputs above the ship channel, including Stockton's wastewater treatment plan two miles up, cities and towns farther upriver, and the 7,300 square-mile watershed, with its large areas of irrigated agriculture, beyond.
Some info already exists. In a review of historical data on nutrient and suspended sediment inputs to the San Joaquin River upstream of Vernalis between 1972-1990, researcher Charlie Kratzer of the U.S. Geological Survey found increasing concentrations of nitrate since the 1950s and decreasing concentrations of ammonia during the 1980s (bacteria in the water convert ammonia into a nitrate, and in the process guzzle more oxygen). What this means, says Kratzer, is that inputs from dairies (ammonia) have gone down with better on-farm management while inputs from irrigated agriculture have gone up (not surprising given widespread tile drain installation in the 1960s and 1970s).
Kratzer's analysis suggests that at least 81% of the nitrogen and 68% of the phosphorous in the river at Vernalis come from nonpoint sources. He thinks any future monitoring of nutrient types and sources should look at "tracers" such as human pharmaceuticals or growth hormones (used in milk production). "Nutrients aren't labeled as coming from land or fertilizers or municipal wastewater, but if you find caffeine you know its coming from a treatment plant not a dairy," he says.
Some of the other big questions the research needs to answer, according to the Central Valley Board's Tom King, include what's going on in the 16-mile stretch of river between Mossdale and the ship channel where some dissolved oxygen is clearly lost. Another big question is which are the things most limiting to algal growth (and thus most worthy of control efforts). Is light the most limiting factor? In a system swamped with more nutrients than algae can use, is nitrogen or phosphorous more important to curb? Recent estimates suggest that phosphorous inputs, for example, would have to be reduced by 100 fold to make a difference, according to Fred Lee. "Nobody's ever done that before on ag land. Even in Chesapeake Bay, with its similar problems, their goal is only a 40% cut."
Likewise, though less ammonia is coming from dairies upstream, ammonia coming from the Stockton sewage plant during low flow periods last fall exceeded levels recommended for the protection of aquatic life, says Lee. Solving this and other wastewater related problems, by investing in a tertiary treatment, will be very costly.
Who will take responsibility for which part of the dissolved oxygen problem is a task slated to be completed by a Steering Committee of stakeholders by 2002. The divvying up - to be achieved via a Regional Board-approved "TMDL" or total maximum daily allowable load for the river - also allocates responsibility for paying for any solutions to the problem.
Insiders think the "solutions" will combine BMPs (best management practices) for agriculture, some tertiary treatment for sewage, installation of some aeration devices in the channel depths; and changes in how and when flows are directed through the offending stretch of river (via reoperation of the South Delta tide gates and barriers). When the Grant Line barrier was opened last fall (sucking water away from the river), flows to the deepwater channel dropped from 800 to 100 cubic feet per second, dissolved oxygen levels halved, and residence time leaped from 10 to 30 days, according to Lee.
Water management aside, environmentalists are worried that even with the TMDL in hand, growth in the San Joaquin Valley's burgeoning cities, and its associated swells in wastewater loads, may just cancel out any progress.
With so many factors to consider and so many who may soon be held accountable, it's no wonder that recent meetings of the steering and technical committees have been somewhat "nervy," say observers. Discussions of how the CALFED workplan should be tweaked to reflect the preliminary data have also been heady. Lehman sounds a little world weary when talking about the committee process. "It's a technical nightmare for scientists to have over 50 people engaged in internal reviews every step of the way," she says.
But stakeholders such as Bob Murdoch of the City of Stockton are encouraged that so many interests have been meeting every month, and that new faces are appearing at the table as more people understand that this may affect them. "First you have to spend the time to understand the problem, so that when you spend the money to fix it, you know it'll be fixed," he says.
Contact: Peggy Lehman (916)227-7551, Tom King (916)255-3105, Fred Lee (530)753-9630 or Charlie Kratzer (916)278-3076
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