The Maryland Department of Natural Resources and other researchers hope the findings of their recent study will result in tighter growth restrictions to help protect brook trout and pristine streams.
The study found that brook trout have disappeared from some Maryland watersheds where impervious surfaces such as pavement and rooftops cover less than 4 percent of the ground. That’s lower than the 10 percent figure generally accepted as environmentally sound for nearly 30 years.
“We may need to think about lower thresholds than the 10 percent rule,” lead researcher and state biologist Scott A. Stranko said last week. “We at DNR are seeing substantial effects on biology at definitely much lower levels than 10 percent.”
The conservation group Trout Unlimited said Maryland’s more than 55 percent of small-stream watersheds across the state have lost brook trout entirely and almost 30 percent contain only small, headwater populations.
The study, published in August in the North American Journal of Fisheries Management, looked at 286 streams statewide, including some repeatedly sampled for brook trout since 1972.
Mr. Stranko told The Washington Times that brook trout likely still exist in such area watershed as the Monocacy and Patapsco rivers and that they probably were in the Anacostia until urbanization.
Brook trout were almost never found in watersheds where impervious land cover exceeded 4 percent, as measured by the 2001 National Land Cover Database of satellite imagery.
Of six streams followed over time, three lost all their brook trout from 1990 to 2005 as urbanization increased, the study found. The amount of impervious land cover in those watersheds ranged from as little as 3 percent to 8 percent.
The best predictor of brook trout occurrence was the amount of forested land in the watershed, but urbanization and impervious land cover also were important, the study found.
Urban-sprawl opponent Richard Klein, who said he originated the 10 percent rule in 1979, agreed with Mr. Stranko’s findings because today’s measurement techniques are more refined than those used decades ago.
Mr. Klein, president of Community and Environmental Defense Services, in Owings Mills, Md., said stream degradation begins with the first house built in a watershed and worsens with each added building, road or parking lot. “It’s just that it’s not detectable until you get a certain amount of development in the watershed,” he said.
Chesapeake Stormwater Network Coordinator Thomas R. Schueler, who also said he originated the 10 percent rule, noted that other recent research throughout the country also indicates a lower threshold for biological harm.
“Communities that want to protect the native brook trout populations have to really exert exceptional land-use control, forest conservation, stream buffers and really first-class stormwater management,” he said. “It’s really a wake-up call to communities to protect their diversity and especially trout, which are a significant part of their tourist economy.”
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