Midges, the bane of fishermen and stream-side picnics, advance with civilization, Virginia Tech biology graduate student Matthew McTammany has discovered. He presented his research at the American Society of Limnology and Oceanography (ASLO) / Ecological Society of America (ESA) national meeting, which was held June 7-12 in St. Louis, Mo.
In research funded in part by the National Science Foundation, McTammany and colleagues investigated the impact of urbanization on the diversity and populations of insects that live some stage of their lives at the bottom of streams. The researchers looked at 12 streams in western North Carolina, counting insects and measuring physical and chemical conditions of the streams. The streams studied come from watersheds that encompass the resort towns of Maggie Valley and Cherokee and the more densely populated Waynesville and Asheville.
Among the insects that have been the most damaged by urbanization are mayflies, stoneflies, and caddisflies, McTammany reports. "They are sensitive to pollution at the larval stages." As fly fishermen know, these insects are popular fish food; when these insects disappear, fish populations are affected.
Left in plentiful supply are midge larvae. "They are pollution tolerant, so you can get thousands per square meter in highly urbanized areas," McTammany says.
While pollution reduces diversity overall it creates advantages for tolerant species. "Their predators may not be tolerant," McTammany says. "Algae, which can be a food source, grows well in urbanized systems in response to runoff from over-fertilized lawns and increased light and temperature from tree removal. Organic matter, also a good food source, can be higher downstream of sewage plants. Finally, tolerant species can have less competition for resources as other species are killed." However, he adds, "some pollution kills everything."
Streams in primarily residential watersheds supported greater diversity than streams in commercial or industrial areas, McTammany found. In the resort towns, he found hotels along the stream corridors and a casino under construction at the time of the study. "There are also golf courses and some houses; but, in the whole watershed, not much development has occurred," he said. However, streams in Asheville and other larger towns have been getting "hit hard" because of runoff from shopping center parking lots, McTammany says. Paved areas result in periodic high washes of water and pollutants into streams. The pollutants are those that land on the pavement, such as antifreeze and oil, as well as sediments containing toxic metals from asphalt.
The research is an extension of five decades of studies of streams in the western Carolina forests by the Coweeta Hydrologic Laboratory, a U.S. Forest Service facility funded by the NSF. McTammany's project is part of an effort to include sites from a larger portion of the southern Appalachians in Coweeta's research program. Other members of the Virginia Tech "Stream Team" (http://www.biol.vt.edu/Facultypages/webster/streamteam/streamteam.html) are investigating logging impact and agricultural impact in many types of ecosystems.
McTammany measured land use within 100 meters of the 12 streams for two kilometers upstream of each collection site. Using Geographic Information System (GIS) data from satellites, topographic maps, and U.S. Geological Survey aerial photos, he measured building density, forest density, and road density for 1970, 1990, and 1997. He drove to every building and wrote down what it is, and imposed a grid on each aerial photograph to calculate the impervious surface (paved) areas.
He also has the benefit of previous research. McTammany 's advisor, Virginia Tech Biology Professor Fred Benfield, is interested in historic land use along streams (http://www.vt.edu:10021/ur/news/Archives/Aug97/97325.html). Because of Benfield's long-term research, McTammany has been considering the impact of previous land use in addition to current conditions. Benfield found that streams in reforested areas show the impact of agricultural land use 40 years ago. But McTammany found that in urban areas, current land use is as important as historical use. "In Waynesville 25 years ago, there were not so many roads and buildings. But the streams' insects are more related to current urbanization rather than to historic urbanization. It's hard for them to deal with the sudden high flows and pollution in runoff from paved surfaces."
McTammany's presentation ("The Impact of Urbanization Type and Degree on Benthic Macroinvertebrates and Stream Quality," on Tuesday, June 9, at 11:10 a.m. in St. Louis Ballroom E of the Adam's Mark Hotel) is part of the special session (SSO1) on "Aquatic Ecosystems in the Urban Landscape."
The research is McTammany's master's thesis in biology. Co-authors are Jonathan S. Harding, a post-doctoral associate at Virginia Tech who is now at Cawthron Institute in New Zealand; Benfield; and P.V. Bolstad and G.A. Edwards of the University of Minnesota's Department of Forest Resources. Bolstad and Edwards provided the GIS data. McTammany will complete his master's degree by the end of June and his thesis will be available electronically from Virginia Tech's library (http://scholar.lib.vt.edu/theses/index.html).
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