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In the Field & Lab
HERBICIDE TESTED ON SLOUGH WEED
Scientists conducting test sprays of the herbicide Komeen on the exotic aquatic weed Egeria densa found that the waterway-clogging plant was better controlled in a single large-scale application than in several smaller ones. The U.S. Department of Agriculture's Dr. Lars Anderson, who was charged with assessing the effectiveness of the Komeen and with measuring the potentially harmful impacts on the water column of the copper it contains, carried out two trials this summer in Sand Mound Slough. In the first, he treated three one-acre areas, applying 16 gallons of the herbicide per acre. In the second, he treated one five-acre plot at the same application rate. The latter approach proved more effective.
Anderson's method involved applying the Komeen at low tide, then testing copper levels in the water every two hours until the next high tide, and in the plants after 24 hours. In the first trial with the one-acre applications, the highest level of copper he found was 0.65 ppm. Within six hours, the level was down to one tenth of this maximum; within 24 hours, it was indistinguishable from background. In the plants, copper levels measured 200 ppm, and biomass decreased by 50-80%. But Anderson says the egeria started to grow back within two weeks. "It's kind of like mowing the lawn," he says.
The second larger trial left more copper - 0.5-1.5 ppm - in the water and increased the egeria's exposure time. Their uptake jumped to a more effective 300-400 ppm, according to Anderson. "The larger plot with the longer contact time at a higher rate gave us a better, more widespread and more uniform reduction of the biomass," he says. Anderson followed up with lab tests to see if the Komeen worked cumulatively, applying the herbicide three days in a row. But by the second day, the plant had little ability left to take up the copper.
"What all this tells us is small treatments may defeat the purpose, which is to minimize the addition of copper to the ecosystem," says Anderson. His results will be considered by state regulators trying to balance water quality impacts with boating convenience and safety. Contact: Dr. Lars Anderson (916)752-6260 8/94
WELL OF UNCERTAINTY
It's a tale of two studies in Chico, where the state's Department of Water Resources and Butte County Supervisors both say science supports opposite positions about the impact of the state water bank on groundwater supplies. "Our model showed twice the effect of what they showed," says Butte Supervisor Ed McLauglin, who believes the state's 1994 purchase of 105,000 acre-feet from two Chico water districts caused wells to be sucked down as much as 30 feet. A model presented by Water Resources to county residents last month, however, shows levels only falling by 5-10 feet, according to the Department's Dan McManus. McManus says Butte's model is not as accurate as his agency's; McLaughlin says Butte's model used far more information. While the latter model spins out more scenarios over the next few months, Water Resources is cooperating with the requests of a coalition of Butte County water districts to suspend purchases from their area. McLaughlin sees this cooperation as a "self-admission" on the Department's part that there is a problem. McManus thinks Butte County has modified a "no-new-wells" ordinance to aim it at areas where potential water bank sellers live. Contact: Ed McLaughlin (916)891-2808; Dave McManus (916)529-7361 10/94
SMELT ZONE OUT
Final results of a summer field study aimed at revealing the real-life interaction between water project operations and distribution and losses of Delta smelt may cast some doubt on longstanding theory on the subject.
"The zone of influence of the pumps under the study's conditions for Delta smelt wasn't as great as conventionally thought," says Leo Winternitz of the Department of Water Resources, which commissioned the research. The study, conducted by Hanson Environmental in June and July 1994, examined whether or not a statistically significant increase in juvenile smelt abundance would occur at sampling locations within the Old and Middle Rivers (generally thought to be within the zone of influence) as a direct result of an increase in water project exports. The relationship was also explored at sampling locations throughout the Delta. The investigation detected no significant change in the distribution of smelt in response to the increased export rate. Indeed, the fish's distribution remained similar during both low and high exports.
"Now we have empirical evidence on actual impacts; before only theoretical impacts have been used to regulate flows," he says, adding that the study only indicates impacts under its specific time period and conditions. The study has been criticized for its timing during a period when critics felt many smelt had moved out of range of the pumps.
Water Resources hopes to conduct a follow-up study next spring, when the smelt are smaller, closer to the pumps and more susceptible to exports. But the recently released draft Fish & Wildlife Biological Opinion on the smelt, which lays down pump management and other conditions for its survival under the Endangered Species Act, may limit fish collection for certain research. Water Resources will be questioning these limitations in its comments on the opinion, according to Winternitz. "Otherwise we're going to have a lot of untested theories," he says. Contact: Leo Winternitz (916)227-7548 8/94
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