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Higher Ground Restoring Healthy Tidal Marsh It’s a sad reality that approximately 90% of California’s wetlands have vanished, largely as the result of diking and draining. Nearly half—about 1,000 acres—of Elkhorn Slough’s historic tidal marshes have been lost since 1870, reducing both wildlife habitat and water filtration. (A football field, minus the end zones, is just about an acre. Imagine 1,000 football fields to visualize the scale of this loss.) From the late-1800s through the mid-1900s, parts of Elkhorn Slough, especially marshes along the slough’s southern and eastern shores, were diked and drained to create pasture and farmland. The land in these former marshes began to subside after it was drained. The once moist and peaty soils dried out and compacted—much like a kitchen sponge shrinks as it dries—and dropped from one to six feet below historic elevations. When the dikes broke or were removed in later years, the drop in elevation meant the marshlands, which before were submerged only intermittently by higher high tides, now are flooded too consistently to support pickleweed and other marsh vegetation. The result: land too high for productive mudflat but too low for tidal salt marsh. In unaltered estuaries, sediment is deposited naturally to wetlands by the outflow of creeks and rivers. Pickleweed can colonize these deposits, trapping
more sediment, which in turn promotes the growth of additional pickleweed. The hydrology (movement of water) of Elkhorn Slough has been dramatically altered over the years—both naturally and by humans— resulting in changes to sediment influx. For example, freshwater sources such as Carneros Creek, Pajaro River, and the Salinas River provide much less sediment than they did historically. Faced with this predicament, the Tidal Wetland Program (TWP)—a collaborative effort of the California Department of Fish and Wildlife and the Elkhorn Slough Foundation—convened more than 100 scientists and resource managers to focus on understanding and restoring the tidal marshes of Elkhorn Slough. After evaluating a wide range of alternatives, it was agreed that the Elkhorn Slough estuary required more sediment to sustain healthy tidal marshes, especially in the face of sea level rise. Continued on page 4
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