Impact of urbanization on fish diversity, composition, and structure of stream food webs along a land-cover gradient in Jefferson County, Kentucky current and historical perspectives.

摘要

Human alteration of watershed land use and cover due to urbanization brings prominent changes in the structure and function of stream ecosystems. To evaluate these impacts from urbanization to the biotic integrity of streams twenty-one study sites from nineteen streams were selected across an urban to rural gradient in Jefferson County, Kentucky. The study sites' aquatic food web, community structure of fishes, water chemistry, and hydrology were used as models to evaluate the potential impacts of land-use and cover differences. Fish community structure was evaluated using the Kentucky Index of Biotic Integrity (KIBI) metric and measurements, Sorenson index, Shannon index, and evenness. To reconstructed the stream food webs, we analyzed the stable isotope signatures of carbon (delta 13C) and nitrogen (delta 15N) in two current years 2002 and 2004 and in historical samples collected over several decades (1950--1989) across many of the same sites along the current gradient. Current stream food webs were reconstructed using fishes, macroinvertebrates, periphyton algae, and detrital leaf material from the twenty-one study sites. The historical food webs were reconstructed using only museum fish specimens. We found urban stream food webs had a total nitrogen (delta 15N) enrichment of 4--5‰ over corresponding pristine rural sites. Carbon (delta 13C) signatures from watersheds with the land-use classifications of suburban and urban showed an increase of 3--4‰ over the "pristine" reference watersheds. Increasing amounts of impervious surface in a watershed affected fish communities as evidenced by decreased KIBI scores, Shannon index, and species richness, as well as decreased darter, madtom, and sculpin counts, number of pollution intolerant species, water column species, simple lithophilic spawners, and percent of insectivorous species, with most of these decreases observed in the urban streams.