Editor’s Comments: What We Talk About When We Talk About Wetlands

There are any number of facts about wetlands that most of us probably know by heart: Wetlands’ ability to store water provides a measure of flood control by regulating water levels. Coastal wetlands and marshes protect the shoreline from erosion and buffer some of the worst effects of storm surges. Wetlands trap sediments, and their aquatic plants help neutralize nutrients and other pollutants. Salt marshes can trap carbon from the atmosphere, potentially storing as much carbon as forested land. Wetlands provide habitat for plants and animals, some of which are found in no other environment. And perhaps the most well-known fact about them: Wetlands are disappearing

In the US we’ve lost, over a couple of centuries of development, more than half our wetlands—more than 87% of that to agriculture. Some areas are notorious: the Florida Everglades, for example, which were enthusiastically drained and filled in to accommodate new cities and new farmland, and which we are now—at great expense—restoring to something resembling (although not exactly) their natural hydrology.

Now, though, agricultural lands throughout the country are giving some of those wetlands and marshes back. It’s a slow process, often expensive, and not perfect. But as we recognize the benefits of what we’ve lost, the move to undo the damage is gaining momentum.

The wetlands surrounding California’s Elkhorn Slough, a 7-mile-long estuary in the central part of the state, are a good example of what can be accomplished. In 1947, the US Army Corps of Engineers, in an effort to create a new fishing harbor, dug a channel at the mouth of the slough. The new channel allowed tides to reach the marshland surrounding the estuary with far more force than in the past, and those marshlands soon eroded.

Other changes also caused damage. To make the area more suitable for growing crops, farmers built a network of dikes and berms to drain the land; the soil and peat on the drained land quickly eroded or blew away as it dried out, and the land subsided by as much as 3 feet. Perhaps just as seriously, agricultural runoff from farms in Monterey County and Salinas Valley caused eutrophication in the slough. A member of the Elkhorn Slough National Estuarine Research Reserve says the concentration of fertilizer on the mud flats reached levels at least as high as on a typical farm field.

Now, through decades of work, more than 6,500 acres of the land that drains to the slough has been restored. Dirt dredged from the nearby Pajaro River to control flooding has been added to the areas of subsidence, and those once-drained areas have been reconnected with the estuary. A salt marsh—and the otters, birds, and fish that go with it—is slowly returning. You can read more about the Elkhorn Slough restoration here.

Two years ago in Erosion Control, we ran an article on two other wetlands-turned-farm-turned-wetlands areas. Titled “Grade-A Restoration,” it details the process of removing levees, backfilling drainage ditches, and “reassembling the watercourses to mimic their original configuration as a web of tidal channels.” In addition to bringing the area back to something close to its original hydrology and habitat, removing the levees had an important benefit for the surrounding homeowners as well: “Relieving the pressure against the walls of the channels and freeing the floodwater from the artificial constraints imposed by the levees means that the water can now disperse over the wide expanse of terrain of the marsh plains, rather than backing up into residential areas.” You can read the article online here.

An upcoming article by the same author will take a close look at two more projects, one along the ­Illinois River and another in North Dakota. Both involve restoring more-or-less natural transfers of water, one between the river and the newly restored wetland area, the other between two adjacent seasonal wetlands.

Are you aware of successful marsh or wetland restoration projects in your area—coastal or inland? Have you been involved in such projects yourself?