Facing a 2025 deadline to clean up the Chesapeake Bay, officials in urban and suburban areas are spending millions of dollars on stream restoration projects. The six states in the estuary’s watershed, along with the District of Columbia, have told the U.S. Environmental Protection Agency that they plan to restore a total of 655 miles of streams. The projects operate on a theory that converting upstream waters from stormwater superhighways to slow lanes would decrease erosion and encourage more water to soak into the ground, reducing the amount of nutrients and sediment heading into the Bay. Now, there is a growing scientific consensus that stream restoration isn’t improving water quality and aquatic habitats as much as was once hoped in a highly urbanized area.
“It’s not a waste of money,” said Solange Filoso, a biogeochemist with the University of Maryland Center for Environmental Science. “But the return on investment is not as high as we thought it would be.”
Filoso has been monitoring the Wilelinor and several other reconstructed streams for about a decade. At first, she was confident she would see significant improvement in water quality. What she found was much more modest: an average reduction of 5–15 percent in nitrogen and 40 percent in sediment.
Some stream restoration projects curb more pollution and others less, given the variations in construction methods and local topography, Filoso said. But she and other researchers studying projects across the mid-Atlantic have collected enough evidence to suggest that stream restoration alone can’t solve the region’s runoff problem. “We are trying to solve a big problem … with a solution that isn’t sufficient,” Filoso said. “The solution being implemented doesn’t match the magnitude of the problem.”
|An Underhill stream restoration|
“I would tell you ecological restoration is not yet a science,” said Keith Underwood, an Annapolis-based contractor who was one of the region’s pioneers in the field, starting his first projects in the mid-1990s. “It’s still very much in the era of an art.”I was involved in the preparation of a proposal for the Smithsonian to work with Underwood on the restoration of stream which was heavily impacted by the acid mine drainage in eastern Maryland. We toured one of his "restored" streams in the Annapolis region during that preparation. It was very pretty to look at, one might almost call it carefully landscaped, certainly an improvement. But they are pretty expensive on a linear basis. It's pretty hard to imagine these restoration practices being practiced on all the streams that could benefit.
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Restored streams only get better with time, proponents say, as the scars of construction heal and nature reasserts itself. But one improvement is obvious almost immediately: Water travels through the channels more slowly. That leads to less streambank erosion and less sediment being transported downstream. Phosphorus, another problem nutrient, clings to sediment. So it ends up staying put rather than being flushed into the Chesapeake.
But there can be downsides, scientists caution. For instance, portions of restored streams can turn into “dead zones” themselves, Filoso said.
One of the main methods that contractors use to slow floodwater is creating a chain of pools separated by rock weirs; they’re embedded in a slope so that one trickles into the next. In warm weather, decaying plants trapped in the slow-moving water can use up its oxygen.
When water turns anoxic, or lacking in oxygen, it can flip that lingering phosphorus from a positive story to a negative one. A chemical reaction unglues the nutrient from the sediment, transforming it into a fertilizer for algae blooms, Filoso said.
“All the restorations have trade-offs,” she added.
There is disagreement over whether the re-engineered streams are providing better habitat for insects, frogs and other wildlife. Studying more than a dozen stream sites in Maryland, EPA researchers Rebecca Cope and Greg Pond found that restored streams weren’t improving aquatic life and, in some cases, were leading to less diversity. All that could be found in some were worms and maggots, Pond said.
Again, the issue seems to be the low amount of oxygen in some restored streams, he said. “The thing with dissolved oxygen is it’s a kill switch. You get below 2 milligrams [per liter], you get a lot of death with macroinvertebrates that may have colonized,” Pond said during a recent conference call with the Chesapeake Bay Program stream health panel.
Underwood was listening, growing frustrated. In an interview later, he called it unfair for scientists to evaluate all restored streams with the same criteria when great variations exist among them. Truly “restored” streams, known in the industry as regenerative stormwater conveyances, or RSCs, re-establish hydrologic connections between channels, their floodplains and the groundwater, he said.
“You saw that our detractors were calling a lot of things RSC that were not RSC,” Underwood said. In one case, he added, “they were studying bugs at the outfall pipe from the Annapolis Mall.”
I didn't stick around to see if they got the money for the eastern Maryland project.
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