| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Habitats A Slough of Hope
Two hundred years ago, the San Francisco Bay Delta spread out into one of the world’s most spectacular wetlands. One thousand square miles of marsh and floodplain were nourished by runoff from the state’s largest watershed. The water coursed through a vast circulatory system of meandering sloughs. Flocks of geese and other migrating birds darkened the sky. Tule elk, grizzly bears, river otters, muskrats, and beavers were all abundant. And the Delta was chock full of fish. The salmon that passed through to spawn upriver once choked the narrow Carquinez Strait. Although much of the Delta still looks old-fashioned and bucolic, it is largely an artificial environment. By the second half of the nineteenth century, the vast expanses of freshwater marsh had been leveed, drained, and converted into fertile agricultural land. By 1960, huge high-tech water projects diverted, in dry years, as much as half the Delta’s original flow to faucets, factories, and farms around the state. The losers in this grand transformation were the plants and animals that relied on the Delta’s marshes as home and nursery, breeding and feeding ground. Today, what was once one of the most abundant Delta environments is now its rarest: freshwater tidal marsh, home to many rare and endangered native fish. So when restoration ecologist John Cain of the Berkeley-based Natural Heritage Institute (NHI) went looking for a suitable piece of Delta marshland to restore, he found he had his job cut out for him. “There weren’t a lot of qualified [site] candidates,” says Cain. “Most reclaimed portions of the Delta have subsided to the point that if you take down the levees that keep them dry, they’d be too deep under water for marsh.” Cain was overseeing an analysis of the entire Delta region on behalf of calfed, a partnership of federal, state, and local agencies responsible for managing the region’s water supplies and improving the quality of San Francisco Bay-Delta habitat. CALFED had identified freshwater tidal marsh restoration as a key component of their plan to restore the Delta ecosystem, and Cain aimed to find the best site for the project. Much of what made Cain’s job so difficult stems from the behavior of Delta land. Underlying the original marshes were meters of organic peat soil, built up over thousands of generations of tules dying, falling, and decomposing. When peat is wet, it holds water like a sponge. When dried, it compresses. And when exposed to air through draining and plowing, it oxidizes, erodes, and shrinks further. Together, these forces have caused the subsidence of many of the Delta’s “islands.” Some are now more than 20 feet below sea level and still sinking. After an extensive search, Cain came upon the 1,200-acre Dutch Slough site, three parcels of “reclaimed” land on mostly mineral soils at the mouth of Marsh Creek. Because the parcels were not composed solely of peat soils, they had largely escaped subsidence. Once flooded, Cain says, Dutch Slough would be the perfect depth for the kind of freshwater tidal marsh most desperately needed by Delta fauna and flora. Dutch Slough, named for the meandering waterway that demarcates its northern boundary, was leveed and pumped dry for agriculture in the 1880s. The 1,230-acre pastoral backwater in Oakley is still owned by three local families who use it for raising cattle and running a dairy. Dutch Slough is at the mouth of Marsh Creek, which drains the east side of Mount Diablo. The watershed is the second-largest and the most rabidly urbanizing watershed in Contra Costa County. By receiving the outflow of the orchards, vineyards, and growing urban areas of the watershed, the marsh’s natural filtering systems could help cleanse the county’s toxic runoff before it reaches the Delta. Furthermore, if the restoration project ever expanded to include the creek, it would provide an important north/south wildlife corridor from the Delta to the headwaters on Mount Diablo. Dutch Slough’s location in the western Delta increases the odds that it will benefit rare natives such as Sacramento splittail, Chinook salmon, and Delta smelt. Splittail, a species recently listed as threatened, depend on inundated marsh and floodplain to spawn and reproduce. Adults congregate near Dutch Slough, where the Delta’s freshwater mixes with the brackish water of Suisuin Marsh. Today, the Delta’s re-engineered channels are a hostile environment for young salmon, but studies from the Pacific Northwest indicate that freshwater tidal marshes are important nursing grounds for the young fish. Cain hopes that young salmon leaving the Sacramento and San Joaquin Rivers will fatten up at Dutch Slough before heading off to sea, increasing the odds that they will return to spawn in the rivers as adults. The Dutch Slough site is broken into three roughly equivalent parcels divided by levees. “That gives us the chance to take an hypothesis-based approach to restoring these marshes,” says Cain. “We can try one method on the first parcel, make adjustments on the second, and then compare results. Most restoration projects are a one-shot deal,” he says. “Here we stand to learn a tremendous amount in addition to restoring critical habitat.” As luck would have it, the families that owned Dutch Slough were looking to sell. As property values in the area soared and the profitability of dairy farming and cattle grazing fell, the temptation to sell became irresistible. In the early 1990s, realizing that they could maximize their profit by selling together, the families forged a partnership. They originally planned to sell to developers. In fact, the families had already obtained a development agreement from the County allowing them to construct 4,000 homes on the site. The newly incorporated City of Oakley was bound by the development agreement and planned to permit development of the site. When Cain recognized the potential value of Dutch Slough and learned it was for sale, he quickly composed a coalition of organizations and agencies including the Coastal Commission to woo the three families with an alternative vision for their legacy. As long as they made their profit, the owners were amenable, even enthusiastic. For one thing, they would get their purchase price all at once rather than over time, the way the developer would have paid them from his profits. But the conservationists still had to sell the idea to the City of Oakley, which had been banking on development of the site to help fund much-needed improvements for the community. To sweeten the offer, the landowners, NHI, and the Coastal Conservancy agreed to set aside 63 acres of the 1,230-acre site for a community park. It would include a swimming lagoon, a network of hiking trails, and a small boat launch. One of the historic dairy homes would be converted into a museum and community center. And the site could also house the proposed Delta Science Center, a research and education institute still looking for quarters. All of these amenities, the Council concluded, would improve the lives of its constituents. And perhaps most important to the Council, the project would draw even more taxpayers into the city’s limits. Despite the opposition of some hardliners on the Oakley City Council, the idea of the park and restoration project was accepted and, in November CALFED dedicated $25 million for the purchase of the site. The Coastal Conservancy threw in another $5 million and has promised to boost that to $10 million once the sale goes through. Dutch Slough’s purchase and restoration, however, aren’t enough to secure the region’s ecological destiny. No place in California is converting open space into houses faster than the region in Contra Costa County just south of Dutch Slough. Nearby Brentwood is the fastest-growing city in California. Between 1990 and 2000 it expanded by more than 200 percent, and the Association of Bay Area Governments predicts that it will double again by 2020. Oakley, whose city limit encompasses Dutch Slough, isn’t far behind. Since incorporating in 1999, it has nearly doubled in size by building about 7,000 new homes. And over 90 percent of the town’s undeveloped land is slated for housing projects. As the towns and cities grow, the rolling hills of oak chaparral, woodland, and riparian habitat will give way to the nauseating swerves of wide streets lined with monotonous two- and three-car-garage homes. Only a stone’s throw south of the new marsh are three more sites, held by the same owners, destined to be plastered with 1,200 houses by 2007. Further south, 5,000 more are slated to be built in Antioch in the next few years. New development proposals will bring buildings up to the boundary of Black Diamond Regional Park and right to the edge of Sutter Creek. The ecological impact of all this development on Dutch Slough, and on the Delta as a whole, is profound. More people will require more clean water from the Delta. And the habits of urban and suburban life create huge quantities of toxic runoff, which will flow into the wetlands. If the watershed is to be encrusted with houses, perhaps at least Marsh Creek could be resuscitated and kept alive. It flows from its headwaters on Mount Diablo through Brentwood and downtown Oakley, and then along the western boundary of Dutch Slough into the Delta. Much of Marsh Creek is now channelized and of little ecological value, but miraculously still supports spawning salmon, rich bird life, and a small population of river otters. When the hills of this area are paved, and the woodlands gone, even the most urbane Contra Costans could come to the creek’s edge and find a glimpse of the living land buried beneath their homes, stores, and roads. And if curiosity leads their wandering steps to its mouth, they would find a rare and vital marsh where that land still spreads out and thrives. Gordy Slack is a freelance science writer and a contributing editor of California Wild. |
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