Teams were headed by specialists and included a wide array of public volunteers, including high school students.
For the participants, the blitz was a round-the-clock event spent turning over stones, shaking branches, and sweeping nets.
The concentrated fieldwork provides important scientific information, organizers say, particularly concerning organisms that usually receive little attention.
The Potomac Gorge event was unusual in that more familiar and better-studied organisms, such as birds, mammals, and flowering plants, were not even counted.
"We wanted to target particular groups of animals that we didn't know a lot about," said Dan Sealy, deputy chief of NPS's Center for Urban Ecology in Washington, D.C.
Researchers did keep a lookout for rare mammals like the Allegheny wood rat, which has not been seen in the area since the 1920s. The rat was not detected.
But most of the focus was on invertebrates, including various groups of insects, which make up the majority of species diversity on the planet.
The thousand-plus species detected during the Potomac BioBlitz are only a fraction of the true biodiversity of the region, researchers say.
No single-day count can substitute for methodical surveying at different times of the year.
But all that effort, experts say, will help more people appreciate the value of a wild and still-functioning ecosystem in a mostly urban setting.
The Potomac River Gorge is considered one of the most biologically important natural areas in the eastern U.S. The area's known diversity includes over a dozen species considered globally rare.
"There's an assumption by many people that if you reside in an urban area, you don't have high biodiversity," Sealy said. "But in the Potomac Gorge, we do."
Stephanie Flack of the Nature Conservancy says the gorge's forests, streams, and wetlands are also important to human quality of life in the Washington D.C., region.
"Its functioning ecosystems contribute to both air and water quality," Flack said. "A large percentage of the metro region's water supply is withdrawn from the Potomac Gorge."
Sam Droege, a biologist with the U.S. Geological Survey's Patuxent Wildlife Research Center in Maryland, helped organize the first BioBlitz held in Washington, D.C., in 1996.
He says green areas in urban centers are vital, because they retain elements of the former landscape.
"Few species depend on these spots for their existence, but from a quality of life, stewardship, and aesthetic perspective they feed our essential nature as people," Droege said.
BioBlitzes have been popular, he adds, because they provide an opportunity for both scientists and the public to look more closely at these important natural areas, which often are taken for granted.
"BioBlitzes explore something unexplored, find things unexpected, and involve a bunch of enthusiastic and slightly eccentric people that the public enjoys getting to know," Droege said.
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