They Paved Paradise and Killed the Fish
Scientists Point to Man-Made Surfaces' Harm to the Severn River as a Cautionary Tale

By David A. Fahrenthold
Washington Post Staff Writer
Thursday, January 11, 2007; AA01


Development along the Severn River, shown here at Arnold, has left about 17 percent of the watershed
covered in hard surfaces, scientists say. Rainwater hitting the surfaces contributes to erosion.
(By Mark Gail -- The Washington Post)

A group of Maryland state biologists, making an unusual series of public appeals about the environmental cost of unchecked development, are using the Severn River as a great example of a very bad thing.

The scientists, leaving their usual realm of laboratories and research vessels, have made presentations to county boards and environmental groups, including some in Charles County. Their message is that when too much of a river's watershed is eaten up by concrete and asphalt, the result is a cascade of mud and pollution that can deplete fish populations.

They say the Severn, where yellow perch populations have dropped sharply as streets and shopping centers have sprouted nearby, makes for a sad Exhibit A.

"It's our poster child for how bad things can get," said Jim Uphoff, a scientist with the Maryland Department of Natural Resources and a leader in the outreach effort. "I say, 'Okay, [if] you guys develop to this level, or past this level, this is what we've seen with yellow perch in the Severn River.' "

The relationship between concrete on the land and fish in the water is not an obvious one. Explaining why one hurts the other requires discourses on the absorbent properties of dirt and the oxygen needs of algae. But Uphoff and four fellow biologists from the Department of Natural Resources are trying to make the connection better known.

They call themselves the Impervious Serfs -- a joke, because they spend most of their time talking about so-called impervious surfaces.

These are parts of the land that have been covered in something man-made and solid, such as asphalt or a house, which water can't easily penetrate. When these hard surfaces cover more than 10 percent of a watershed, the area of land from which rainwater drains to a stream, problems begin to abound.

That's because the surfaces short-circuit nature's way of dealing with rainwater. Before the land was settled, the scientists say, the water would usually soak into the ground and would release slowly into creeks and streams.

But now, rainwater hitting hard surfaces is shunted into storm drains, moving at high speed. It erodes loads of dirt, which clouds the water, buries plants downstream and brings toxic chemicals and other pollutants that feed unnatural algae blooms.

These blooms are a particular problem because they consume underwater oxygen, which fish and crabs need to breathe.

"It's not just one thing," Uphoff said during an interview at his office across the Chesapeake Bay from Anne Arundel County in Stevensville. "It's multiple. There are multiple insults to the system."

There are problems with uncontrolled, polluted storm water all over the Chesapeake region: The Anacostia River, for instance, has historically had some of the worst troubles, with a watershed that is at least 23 percent covered in impervious surfaces.

But the scientists use the Severn as their example because they have studied its decline so closely. Until the 1950s, the Severn had so many yellow perch that state officials took fish from there to start their hatcheries. But then came waves of development -- weekend cottages, then a web of waterside neighborhoods -- that have left about 17 percent of the watershed covered by hard surfaces, they say.

The impact of that development has shown up in a crash of the yellow perch population, officials said. Eggs do not hatch, possibly because of toxic contaminants or a low level of oxygen. Even adult fish that migrate in from other areas are under stress in the Severn, trying to find a place where they can breathe.

One statistic hints at the scope of the problem. Before 1955, state officials estimate, somewhere between 60 and 98 percent of the yellow perch eggs in the Severn were viable, or capable of hatching fish larvae. Now, about 10 percent are.

"You end up with murky water. You end up with reduced wildlife habitat. You end up with lousy yellow perch habitat, for example," said John Page Williams, a senior naturalist with the Chesapeake Bay Foundation who has studied the Severn and the creeks that feed it. When you develop an area like the Severn's watershed, Williams said, "the tradeoff is in the creek and the river."

After studying the Severn, Uphoff and the other biologists embraced a new trend in the world of wildlife management, in which biologists try to prevent fish population declines before they occur. They have set up a presentation that explains the consequences of increasing impervious surfaces beyond the 10 percent threshold.

So far, they have presented it to a group concerned with the Choptank River, whose watershed on the Eastern Shore is still largely rural, and to Charles officials considering the fate of Mattawoman Creek. The Mattawoman, a Potomac tributary, is frequently cited as one of the best-preserved waters in the D.C. area, with large populations of bass and other fish. But more growth is projected there.

"We're kind of taking it on the road and trying to at least make [people] aware that there's a limit" to what watersheds can take, Uphoff said.

Jim Long of the Mattawoman Watershed Society said that environmentalists appreciated the help. Officials in the county are considering how to curb growth and by how much.

"These folks have the degrees that are needed; they live it," Long said. "So people are going to believe them more than they're just going to believe an activist."

The long-term prospects for the Severn are also murky. Environmentalists say that more recent developments have done more to control storm water and that they have seen rebounds in oysters and underwater grasses. But scientists say it is unclear whether the treasured yellow perch will ever return to their previous populations.

"They're drop-dead gorgeous. They're fun to catch. They're good to eat," said Williams, the bay foundation naturalist. "You really lose something when you start losing these fish."

(Revised Jan 2007)