By Scott Learn, The Oregonian
on November 15, 2012 at 3:16 PM, updated November 15, 2012 at 3:17 PM
Development in western Oregon and southwest Washington has largely swapped forests for homes, driving down water quality and quickly killing off some species of mayflies and other sensitive insects that rely on relatively pristine streams, a new study from the U.S. Geological Survey finds.
USGS researchers examined nine broad urban regions across the United States for their study, released today. In the Northwest, they tapped into 28 measuring stations from Cottage Grove, south of Eugene, to Battle Ground, north of Vancouver, covering the Willamette Valley and the Portland region.
Forests start off with a greater diversity of species and better water quality than agricultural lands, said USGS scientist and study co-author James F. Coles. So regions that focus development on former forest land, including western Oregon, saw the sharpest quality declines, Coles said.
Paving over forestland denudes streamsides and increases runoff from storms. More rainwater gushes into streams, carrying pesticides, fertilizer and sediment and increasing water temperatures, all threats to aquatic life.
“It’s not one thing or the other,” Coles said. “It’s temperature, flashing of streams and washing off of contaminants.”
The Oregon and Massachusetts study areas saw the biggest decline in “sensitive invertebrate species,” the study found, including mayflies, stoneflies and caddisflies, insects familiar to fishermen and long used as indicators of stream health. They decline sharply even in the initial stages of urban development, the researchers said.
The study highlights the need for forest conservation, the researchers said. Other solutions, many being pursued in the Northwest, include planting trees, installing pervious pavement and increasing buffer zones around streams.