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SPECIAL BAY-DELTA SCIENCE CONFERENCE EDITION
Part Two
October 4, 2018
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ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special three-part edition of Pearls shares more than 20 takeaways. Today’s stories highlight presentations on habitat and restoration.
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Given that the historic Delta is gone forever, how much floodplain habitat should we restore, and where? This question occupies many contemporary Delta scientists, such as Rene Henery, California Science Director at Trout Unlimited, who identified a range of factors that influence habitat quality for young Chinook salmon including flood timing and duration; water depth, velocity, and temperature; and available cover. Meanwhile Jacob Katz, a senior scientist for CalTrout, has made it his mission to reconnect the channelized Sacramento River to portions of its historic floodplain in order to slow water and grow food for imperiled native fish. “When you’ve lost 95 percent of your floodplains and your wetlands, why are we surprised when we end up with 5 percent of our fish biomass?” he asks. Other efforts to support floodplains as fish nurseries include the Nature Conservancy’s Emigrating Salmonid Habitat Estimation model for quantifying habitat needs; UC Merced postdoctoral researcher Alison Whipple’s PhD study on quantifying potential habitat benefits for Sacramento splittail at a restoration project along the Cosumnes River; and American Rivers’ Chinook Salmon Habitat Quantification Tool. “This feels like something that people are converging around,” said Henery. NS
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Delta habitat restoration dreams are getting real. After helping define what makes a good Delta project—large rather than small, linked rather than isolated, and so on—the San Francisco Estuary Institute is creating mapping tools to show just where new habitats might be created, and to assess the probable gains. For instance, the Central Valley Joint Venture calls for restoring 84,000 acres of oak savanna across the whole Central Valley. “There’s the potential to support about 30 percent of the objective in the Delta,” says SFEI’s Sam Safran. Such precision, inevitably, makes landowners nervous. “Any time you’re putting opportunities on the map in the Delta, it’s a little bit dicey,” Safran acknowledges. For now the emphasis is on fleshing out what can be accomplished on public lands and through the in-the-pipeline projects of EcoRestore. More controversial steps, some of them identified years ago, have been deferred by Delta planners and managers in the hope that consensus will build. JH
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Franks Tract, a flooded island in the heart of the Delta, is a hotbed for predatory non-native fish–but native fish may still be able to thrive alongside them. “We’ve gone from the old ‘all introduced predatory fish are bad’ to reconciliation,” says Carl Wilcox of the California Department of Fish and Wildlife (CDFW), explaining that this means acknowledging the Delta as a novel ecosystem rather than trying to restore what once was. Historically, Franks Tract was part of a huge marsh, sheltering small fish in channels that meandered into dead ends rather than interconnecting. “Now, there are all kinds of connections that never existed,” Wilcox says. A CDFW-led restoration plan is in the works to reclaim part of Franks Tract for native fish, creating marshes with waterways called dendritic blind channels. These dead-end waterways narrow progressively, subdividing into ever-smaller branches that provide refuges for native fish fleeing from non-native predators. RM
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Barring human intervention, important marsh and mudflat habitats around the Bay are doomed to disappear as sea levels rise. Two new studies, one on each shore of San Francisco Bay, underscore the challenge. A team from Point Blue and San Mateo County examined the county’s wetland fringe. Even with optimistic assumptions about sediment, these marshes will lose ground after 2050 and largely convert to mudflats by 2100; marsh-dependent bird populations will follow suit. On the Bay’s opposite shore, the USGS considered the probable fate of two mudflats, a shallowly sloping expanse at Eden Landing and a narrow, steeper strip near the Dumbarton Bridge. By 2100, a USGS and UNESCO-IHE team reports, the Dumbarton tract will lose 57 percent of its foraging habitat for shorebirds, and the Eden Landing tract 100 percent. “We’re seeing extensive loss of foraging habitat and key prey items,” says the Survey’s Susan De La Cruz. “But it’s not all doom and gloom.” On both shores, results like these will inform new adaptation plans. JH
Photo: Rick Lewis
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Intact transition zones—strips of ground that are only occasionally inundated and blend features of uplands and adjacent wetlands—are far rarer and much less studied than salt marshes around San Francisco Bay. Looking at the needs of birds, Nadav Nur of Point Blue and his colleagues posed the question: “When we restore or design transition zones, what should they look like?” Studying 16 sites—some natural, some restored, some with and some without levees—the team concluded that one important plus is simply space: the wider the zone, the better, especially for rails. A second need is tall vegetation to make hiding places; what species of plant provides the shelter doesn’t matter. Sparrows like vegetation to be dense as well as tall. Marsh birds used gentle slopes as well as steeper ones, like levee faces, provided they were well vegetated. Nur urges transition zone restorers to mix and match, trying out a variety of designs. JH
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At the nexus of flood protection and habit restoration is the Bay’s latest craze: living shorelines. Out are steep seawalls and traditional levees. In are low-slope horizontal levees, which after proven success at San Lorenzo’s Oro Loma site could help protect sections of the Bay shore from sea level rise, while providing a range of habitats from mudflat to grassland, said Marin County principal planner Chris Choo. Also in are subtidal oyster-and-eelgrass beds to reduce wave energy and mitigate sea-level rise, such as at Richmond’s Giant Marsh, which the State Coastal Conservancy will restore next year after learning from a smaller project in the San Rafael Bay, said Michelle Orr of Environmental Science Associates. And so is the use of sediment, where space permits, to build ecotones that smoothly transition from tidal marsh to lowland terrestrial to upland, allowing habitat to migrate landward with sea-level rise, such as in the revised restoration plan at Contra Costa County’s Lower Walnut Creek. “One of the big shifts that occurred was to think of [existing] dredge material not as something that needed to be removed, but as a resource,” said Orr. NS
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The Bay Area’s twin needs for new housing and new infrastructure may present an opportunity to boost ecosystem services in our highly altered landscape. So says Letitia Grenier of the San Francisco Estuary Institute, who envisions a Bay Area-wide plan to restore natural processes, not “just” natural habitats. One promising approach—originally developed by Erica Spotswood and Robin Grossinger—is strategic planting of native oaks to conserve water during the dry season and reduce runoff during the wet season. Trees also store carbon and reduce urban heat islands. All told, native oak trees account for five percent of the street trees in Silicon Valley but provide nearly 10 percent of tree-related ecosystem services. “Native oaks punch above their weight,” Grenier says. RM
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Look for Part 3 of this special Science Conference edition of Pearls, featuring stories on climate, water quality and more, on Friday.
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Editor: Cariad Hayes Thronson
Contributors: John Hart, Robin Meadows, Nate Seltenrich
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