Point Reyes Light - March 25, 2004
Mercury spike in Soulajule fish
By Ivan Gale
Fishermen frequenting Soulajule Reservoir along Marshall-Petaluma Road can expect to see warnings about high mercury levels found in the reservoir’s fish habitat. Marin Municipal Water District, which owns the reservoir, said this week the water is still safe for drinking.
The results of recent Regional Water Quality Control Board studies found some largemouth bass have as much as five times the recommended level of mercury for human consumption, said spokeswomsn Dyan Whyte. Tested black crappie and channel catfish, which also inhabit the reservoir, are below the mercury limits.
Some 45 bass were tested in three groups, with one group recording 1.87 parts mercury per million. Other samples averaged .4 parts per million. The recommended limit is .3 parts per million.
No cause for concern
State officials said these numbers are not cause for immediate concern for most fish consumers.
"When we issue advice, we’re really making sure that pregnant women aren’t consuming this fish in excess," Whyte said adding that developing fetuses and young children, whose brain and neurological development is still underway, are most susceptible to harmful effects of mercury consumption.
Bob Castle, a water-quality specialist with the water district, said regular testing reveals Soulajule water is clean of mercury or other hazardous metals pesticides.
"Bio-accumulation is how elevated [mercury] levels in fish occur not only in Soulajule," he said, "but in Tomales Bay, the ocean, in San Francisco Bay, and other waterbodies around the world."
Mercury located in sediment is first taken up by tiny plants and animals like plankton, Castle said, This in turn becomes food for smaller aquatic creatures, which are eaten by larger aquatic creatures. The most-active predators accumulate more of the element, Castle said, noting that fish on the top of the food chain can have as much as 100,000 times the amount of Mercury as the smallest aquatic creatures.
Mercury mine
Staffers at the Regional Board are trying to understand the impact of mercury mining in the watershed.
The large Gambonini mine downstream from the reservoir was capped in 1970 after being mined since 1947.
However, before the reservoir was created in 1978, similar mines were opened on the neighboring ranches of Bill Barboni, Earl and Peter Dolcini, and Bob Dolcini. The mercury was transported to the Gambonini site for processing.
It is possible other smaller mines could have been submerged when the reservoir was created, Whyte said.
"The question is was this the result of mining activity per se... or the effect of mercury naturally occurring portions of the Coast Range?" Whyte explained.
Soulajule, the third largest reservoir of seven within the water district, was built in 1978 to provide water during times of drought. After this winter’s rains, the reservoir is at full capacity, holding 10,572-acre-feet of water.
During times of use, water is pumped across a high ridge into Nicasio Reservoir, where it is pumped again into the district’s water treatment and distribution system.