Level Of Taxonomic Resolution And The Response Of Lotic Invertebrate Communities To Increased Watershed Imperviousness (presentation)

GRESENS, SUSAN*, Kenneth T. Belt, Daniel C. Gwinn, Patricia Banks, and Jamie A. Tang

Urban development greatly increases the proportion of a watershed which is covered by impervious surfaces such as roofs and pavement. We measured the response of stream invertebrate community structure to sharp increases in watershed imperviousness. Monthly samples were taken from riffles in Oregon Branch and Deep Run. In each stream, two "upstream" sites draining woodlands and fields were compared with 2 "downstream" sites receiving runoff from industrial/commercial parks. Principal Component analysis indicated that there were persistent changes in community structure which paralleled the change in land use. When taxa were identified to Order level, the first principal component (PC) showed that upstream sites had greater abundance of Trichoptera, Ephemeroptera and Coleoptera and less fine particulate material on substrata, in contrast to downstream sites. In both streams, the second PC indicated an increased abundance of Diptera at downstream sites. In a separate analysis, larva of Family Chironomidae were identified to Genus, and analyzed similarly. PC scores of chironomid composition also distinguished between upstream and downstream sites. In both streams, Rheotanytarsus sp. and Eukiefferiella sp. predominated at upstream sites, while Orthocladius sp. was associated with downstream, urban sites.