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Linking stream ecosystems and landscape trajectories in the southern Appalachians.
Gardiner, Ned*,1, Sutherland, Andrew2, Meyer, Judy2, Pringle, Cathy 2, Helfman, Gene2, Benfield, Fred3, Bolstad, Paul4, Wear, David5, 1 American Museum of Natural History, New York, NY2 Institute of Ecology, Athens, GA3 Virginia Polytechnic Institute, Blacksburg, VA4 University of Minnesota, St. Paul, MN5 US Forest Service, Raleigh, NC
ABSTRACT- We established an innovative procedure to examine relationships between catchment land use and stream ecosystem structure which guided predictions of future stream ecosystem states in western North Carolina. We chose eight stream sampling sites with similar elevation and catchment sizes representing three distinct categories of land-use history: "forested" (n=2), "rural" (n=3), and "suburban" (n=3). Algal biomass (Chlorophyll-a g m-2 and ash-free dry mass mg m-2), median substrate particle size, sediment core particle size distributions, and total suspended solids (mg l-1) measures did not differ among these groups. By incorporating previously-collected data from the study area, clear patterns were evident for fish assemblages and other water quality parameters. Ordination of fish collections data suggested four categories of streams with distinct catchment land uses in both 1970 and 1993: "forested", "rural", "suburbanizing farmland", and "suburban/urban". The percentage of omnivorous and of widespread fishes increased at sites with "forested", "rural", "suburbanizing farmland", and "suburban/urban" catchments, respectively. Invertivores, lithophilic nest spawners, and fishes with restricted ranges decreased in percentage across that set of categories. As expected, NO3, K, Ca, Mg, and mean summer/fall temperature each increased in the stated order. Ecological integrity was maximal in rural watersheds and minimal in urban ones. We used these observations to extrapolate potential stream ecosystem states in 149 catchments of similar size throughout four large basins in western North Carolina. Based on our observations, we infer two trajectories of possible future stream ecosystem responses to likely future land use changes. If building and road densities increase, streams in forested watersheds are likely to become warmer, higher in nutrients, and support more omnivorous and widespread fishes; proportions of invertivores, lithophilic nest spawners, and endemics would decrease. In suburbanizing farmland catchments that become more like suburban/urban ones, the same predictions hold.
Key words: landscape, socioeconomic model, watershed, forecasting