The afternoon tour that I'm leading at the Elkhorn Slough Reserve is not off to a promising start.
Although it's midsummer and we're standing at an overlook that usually offers panoramic views of California's second-largest salt marsh, a stubborn blanket of fog shrouds the Reserve. The eight visitors in my group pull their jackets tighter against a bone-chilling wind. No one looks very happy.
Even the slough's most conspicuous landmark, the twin 500-foot stacks of the Moss Landing Power Plant on the Monterey Bay, is sheathed in white. Thinking it's best to start moving, I lead the group down the trail. Along the way, I tell them how the 1,400-acre Reserve -- if they could only see it -- is one of the West's most significant birding areas as well as habitat for several rare plant communities and more than a dozen threatened or endangered species.
I point out some barely discernible low-lying islands surrounded by the slough's slate-gray water. It's the water -- and the tug of the tides -- that I most want to talk about today. That seemingly placid water poses a hidden threat to Elkhorn Slough.
Estuaries like Elkhorn are among the most productive natural systems on earth. But unless something is done to slow widespread tidal erosion caused by human alteration of the slough, within our lifetimes this rich marshland will disappear, joining the 90 percent of California's tidal wetlands that have already been dammed or diked or paved over.
In May 2003, I stood for the first time at the Elkhorn Slough overlook. It was twilight, and I was early for the initial meeting of a summer-long docent-training program. I had wandered out to the overlook to view the hundreds of acres of tidal marshes and mudflats that stretch to the horizon. From a distance, I could hear the cur-lee calls of a long-billed curlew.
Boyhood memories of ranger-led talks around evening campfires had left me with a long-held desire to become a volunteer naturalist. On a whim, I called the slough and asked about their docent program. By coincidence, the only docent training of the year was starting in five days. There was one space left. Would I like it?
So there I stood, breathing the salt air, when a powerful rumble came from the north end of the slough. A half-mile-long freight train appeared, chugging over the water across a series of levees. How strange, I thought. Why build a railroad track through a wetland?
From the overlook -- if you can ignore the train track and the towers of the Moss Landing Power Plant -- the slough appears natural. But for thousands of years humans have altered this estuary. During docent training we heard from historians who described how indigenous tribes fished the slough's waters and set fires to keep the grasslands open for hunting. When Europeans arrived, they stripped the oaks from the nearby hills and planted fields of wheat and barley. In 1872, the Southern Pacific Company built a main rail artery through the slough that is still in use today. As time passed, a complex system of dikes and levees spread across parts of the marsh, and some of it was converted to farmland.
After World War II, what is now California's largest power plant was built at the slough's entrance. Every time I come here, I am struck by the incongruity of this natural gas-fired behemoth at the entrance to a vital estuary. The Escher-like maze of the plant's pipes and towers are a monument to the days when wetlands like these were viewed as useless swampland that ought to be "reclaimed."
Then came the Army Corps of Engineers, who changed the slough profoundly. In 1946, they bulldozed a channel through the sand dunes at the slough's entrance to create Moss Landing Harbor. Breaching the dunes opened the slough's quiet brackish lagoons to the power of the tides. The new harbor mouth allowed "tidal scour" to begin to erode away the salt marsh that is crucial habitat for more than 200 bird, marine mammal and fish species. By 1979, when Elkhorn Slough became part of the National Estuarine Research Reserve system, the marshland was degrading at a rapid rate.
In seven years of leading tours at the slough, I've watched as the water's daily ebb and flow has deepened and widened the channels, causing the tidal currents to run faster. Tidal creeks that prior to the dredging of the harbor averaged eight feet in width have expanded to more than 40 feet and are wearing away vital roosting and nesting areas. The reclusive California clapper rail, which once lived in Elkhorn's marsh, has not been seen here in 30 years. A number of other threatened species are also imperiled by erosion, including the western snowy plover, Santa Cruz long-toed salamander, tidewater goby, California brackishwater snail, and California red-legged frog.
Currently, the equivalent of 10,500 truckloads of sediment sluices into the Monterey Bay each year. Half of the slough's tidal marsh has already been lost. If nothing is done, the rest of the marshland will be gone within 50 years.