Blacksburg, Va. -- Virginia Tech biology researchers have applied tools from geology, geography, and hydrologic modeling to determine the effect of different land uses on stream quality across 10 watersheds of the French Broad River in the North Carolina mountains. The result is a new protocol for determining the health or condition of huge land-water systems. The research has also resulted in a set of tools for predicting the effect of development decisions in the watersheds studied, which are near Ashville, N.C.
Biology professor Maury Valett, recent doctoral graduate Chris Burcher, and biology professor Fred Benfield will present their research at the Geological Sciences of America national meeting in Salt Lake City Oct. 16-19.
Valett and Burcher use the "domino effect" as an analogy to describe their research process. "When you knock down a string of dominos, the first one is the stimulus and the last one to fall is the response," said Valett. "We are looking at all the important entities in between." The stimuli include such land uses as parking lots, farms, and urban development. The entities are components of stream – land ecosystems.
The scientific term is "path analysis" and it is a statistical process more often used in social sciences than physical sciences, Burcher said. But he found it a valuable approach for accounting for the multiple influences of different land uses on how disturbance is translated across landscapes. "The 'land-cover cascade' approach helps identify the specific pattern whereby earth manipulation results in erosion and sedimentation that combine to influence the organisms that live in streams," Burcher said.
"We would like to follow a particle from a parking lot to a stream, but we can't do that so we allow path analysis to show us how the dominos are falling," said Valett. "A realistic goal is to try to figure out where you can prop up a domino or take one out to manage a situation to improve stream health."
Burcher said 10 watersheds provided a good representation of the range of what humans are doing to the landscape. He had to learn to use geographic information systems (GIS) and hydrologic modeling to observe land use at that scale, however. He used Landsat imagery in GIS to identify three land uses – agriculture, urban, and forested, within zones where water and sediments differentially moved or settled.
Burcher was back in his own field when it came to measuring responses. The lives and times of stream fish and insects were summarized by 13 metrics that indicated when a cascade of terrestrial events caused significant aquatic damage.
Land use can cause erosion, change bank height or steepness, change stream shape, water speed, deliver sediment to make for a muddy stream, or can change the chemistry or structure of the streambed. Bugs, such as stoneflies and mayflies, are signs of a healthy stream because they process energy and matter – that is, they eat leaves and then are eaten by fish. If the insect population becomes one that derives energy from algae, for instance, the balance changes.
"Total density of fish was one of the best models for stream health," Burcher said.
Valett, Burcher, and Benefield's talk, "The Land Cover Cascade: Linking terrestrial and aquatic subsystems.," will be part of a special session at the GSA meeting organized by Virginia Tech geosciences professor Madeline Schreiber and Valett to present biology-geology approaches to studying the flowpaths that integrate terrestrial and aquatic ecosystems.
There will be presentations from several universities, including two more from Virginia Tech, at the session, which will be from 8 a.m. until noon on Oct. 16 in Salt Palace Convention Center room 251 C.
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