Fears of water weed at popular river parkBiologists testing shoreline cordgrass to see if S.F. Bay invasion has spread northPublished: Wednesday, Dec 13, 2006By COREY YOUNG ARGUS-COURIER STAFF A notorious, fast-spreading cordgrass already choking off waterways in the eastern and southern reaches of San Francisco Bay may have taken hold in the Petaluma River, scientists and environmental advocates say. Three weeks ago, officials from several agencies plucked blades of the suspected grass from the shoreline of Petaluma’s Shollenberger Park, gathering samples to be tested at a University of California, Davis laboratory. They want to know if the clumps of cordgrass, also called Spartina, are the native species or an invasive version originally introduced in the East Bay three decades ago to shore up levees. A greater fear is that the unusual grasses seen along Shollenberger are hybrids of the native and non-natives species. “The visual appearance makes them think it is the invasive hybrid,” said David Yearsley, the executive director of Friends of the Petaluma River, who joined representatives of Fish & Game, Petaluma Wetlands Alliance and the California Coastal Conservancy’s Spartina project on their Shollenberger visit. The presence of the hybrid or the original invasive species, Spartina alterniflora, could be troubling for the Petaluma River and its meandering sloughs and marsh channels, Yearsley said. “It overpowers the local variety and forces out other plants,” he said. Cordgrass can spread quickly over tidal mudflats that serve as foraging habitat for shorebirds and other small creatures, he said. “Once we’re infested, it could spread throughout the watershed,” Yearsley said. He investigated reports of non-native Spartina in Petaluma three years ago but found nothing. Today, though, there’s a possibility infestations in other parts of the bay have produced seeds carried up to Petaluma by the tide, he said. Dr. John Shribbs, a Casa Grande High School biology teacher and a board member of Friends of the Petaluma River, has mapped suspected Spartina sites along the river near Shollenberger to help botanists study the situation, Yearsley said. “At this point, it looks like scabs on the shoreline,” he said of the plant. The non-native cordgrass is taller than the native variety, according to the Spartina project. Its leaves are a reddish-brown color on the bottom while the native grasses are white and green. Since it grows faster than the native grass, Spartina alterniflora or its hybrids can quickly close off waterways and slow down the water — causing more sediment to build up and creating potential flooding problems by raising the channel’s elevation to that of the surrounding land, the group says. In other parts of the bay, low-toxicity herbicides have been used to eradicate Spartina infestations. Results of testing on the Petaluma grass samples should be completed by the end of December. |
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