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Go DeeperThe Nature Conservancy in Oregon Explosives Aid Wetland Restoration in Klamath Basin The Conservnacy's Global Freshwater Team |
Kidney Failure
There are about 108 million acres of wetlands in the lower 48 states. They come in myriad forms, ranging from river deltas like that of the Williamson to low-lying forests in the floodplains of rivers and streams. They take the form of marshes and bogs, coastal salt marshes and mangrove swamps, and even seasonal waterholes in deserts. Whatever their form, wetlands tend to be places of incredible biological productivity, providing habitat for fish and amphibians and food for migratory birds. In terms of biodiversity, wetlands are disproportionately important in relation to their size, sustaining ecosystems over a scale that ranges far beyond the wetlands themselves.
Hydrologists often refer to wetlands—somewhat unglamorously—as the kidneys of the landscape, because they purify the water that flows through them. They also provide one of the main paths for water to percolate into groundwater aquifers, which then slowly mete out water to streams and rivers. “Groundwater is sort of a delayed feed to the stream system, and you tend to get cooler water available in dry and hot times of the year,” says Brian Richter, who directs the Conservancy’s freshwater work. “The flip side is that wetlands can be really important natural storage areas for floodwater, which helps mitigate and attenuate flooding.”
But wetlands face tremendous threats. Agricultural and urban development, as well as dam building, has destroyed more than half the nation’s original wetlands: More than 113 million acres have been lost in the lower 48 states, and in some states—particularly where farming is widespread—wetland losses have been as high as 90 percent. “Wetlands were always such a tiny fraction of the overall landscape to begin with, and they have been hit very hard,” says Richter.
It will likely get worse. In 2006 the U.S. Supreme Court handed down a controversial opinion that federal wetland protections under the Clean Water Act apply only to “navigable” waterways. This ruling could strip protection from nearly 60 percent of the nation’s wetlands.
As those setbacks have cast a cloud over the future of wetlands in the United States, the Conservancy and other nonprofit conservation organizations are playing an increasingly important role in protecting and restoring these crucial swamps, marshes, pools and bogs.
The Conservancy’s freshwater team does a sort of habitat triage, focusing protection efforts on those wetlands that are most important to the biodiversity of a particular region. But in many areas, wetlands have been hit so hard that there are no pristine examples left to acquire. In such places, the Conservancy must work to rehabilitate key areas that have already been damaged or destroyed.
As a result, the Conservancy has honed its expertise at figuring out how to remake intensively engineered river and wetland systems that have lost much of their ecological integrity. Reviving heavily manipulated ecosystems can often take a considerable amount of reverse engineering, of which Jerry Wallace’s explosives work is one extreme example. It has also proved to be an immensely challenging learning process.
“The key is, what’s the greatest affliction? What’s really driving the degradation of the system?” says Richter. Historic alterations to water flows are frequently the “master variable,” he says. “In many cases, flow will be the place where we start, and we’ll see how the system responds.”
The Lower Roanoke River in North Carolina is a prime example of the havoc that a dam can wreak on a river’s natural flow patterns. For 137 miles before it empties into Albemarle Sound, the river’s floodplain is covered with hard-wood forests and cypress-tupelo swamps. The Roanoke is home to the American alligator and short-nosed sturgeon—both of which are on the federal list of endangered species. The river is also home to three hydropower dams run by the Army Corps of Engineers and Dominion Generation, a publicly owned utility.
While the bottomland hardwood forests in the floodplain evolved to withstand short periods of flooding, they have been overwhelmed by the massive, sustained pulses of water released through the dams to generate electricity. Sam Pearsall, the director of science for the Conservancy’s North Carolina chapter, says, “The thing we’ve had to do for the last 16 years is talk Dominion and the [Army] Corps into operating their dams in ways that are less destructive for the downstream ecosystems.”
Returning the river’s flow to a more natural pattern would minimize the amount of time that the floodplain downstream is inundated. The negotiation process has not been easy. “Everybody’s been dancing around each other with guns and Bibles,” says Pearsall. But this year, for the first time, the Army Corps is modifying water releases from Kerr Dam, which causes the majority of the flooding.
Dominion Generation, in turn, has agreed to a 40-year program under which it will monitor and potentially modify the flows from its dams, farther downstream, to help hardwood seedlings re-establish themselves in the floodplain.
“It’s a huge step,” says Pearsall. “It’s the most significant thing that’s happened on the Roanoke since I started working on it.”
Nature picture credits: Illustrations © Alan Daniels
