Streams, Rivers, Slow to Recover Biodiversity After Ag Damage

Virginia Tech researchers, in collaboration with colleagues from the University of Minnesota, traveled through time by comparing sequences of topographical maps and aerial photos dating back to the 1950's with modern satellite images of land-use in North Carolina. This information was entered into a geographic information system (GIS) to create overlays of land-use along streams in the French Broad and the Little Tennessee river basins -- both tributaries of the Tennessee River in western North Carolina.

Then they examined the biodiversity -- the variety of organisms -- in 24 streams: six draining primarily agricultural and six draining forested areas in each basin. "We sampled stream invertebrates including aquatic insects, crayfish, and snails in the 24 streams" explained Fred Benfield, professor of ecology, and his colleague, Jon Harding, a research associate from New Zealand.

The diversity of stream invertebrates was generally greater in forested than in agricultural streams, they found. However, the researchers were surprised to find that in some streams passing through areas that had significant forest regeneration over the last 50 years, the invertebrate diversity was similar to that of streams in present-day agricultural areas.

"Our findings suggest that forest regeneration may alleviate some of the detrimental physical effects of long-term agriculture; however recovery of stream biodiversity to pre-disturbance levels may take many years," says Benfield.