The Response of First and Second Order Streams to Urban Land-use in Maine, U.S.A.

Chandler C. Morse, PBS&J/Univ. of Maine
Alex Huryn, University of Maine Department of Biological Sciences
Chris Cronan, University of Maine Department of Biological Sciences

The Response of First and Second Order Streams to Urban Land-use in Maine, U.S.A.

C.C. Morse, A. Huryn, and C. Cronan
University of Maine
Department of Biological Sciences
Orono, Maine

Physical, chemical, and biological characteristics of streams draining 20 catchments in Maine, U.S.A. were compared to determine the influence of increasing urban intensity on stream ecosystem structure. The catchments had varying levels of urban intensity (percentage of the catchment under impervious surfaces) ranging from 1-31%.

Stream stability, habitat, and water quality consistently decreased as the proportion of impervious area increased within the catchment. Indices describing stream benthic macroinvertebrate communities showed stronger declines as a function of increasing impervious area.

Streams draining catchments with levels of impervious surfaces < 6% had higher levels of total and Ephemeroptera + Plecoptera + Trichoptera (EPT) taxonomic richness. With increased levels of imperviousness, benthic macroinvertebrate communities were characterized by decreased numbers of sensitive taxa. Taxa considered to be moderately sensitive to anthropogenic stress (e.g. Acerpenna (Ephemeroptera), Paracapnia (Plecoptera), Optioservus (Coleoptera), Hydropsyche (Trichoptera)) were little influenced by increasing urban intensity.

Results indicated that beyond an apparent threshold of ~6% impervious surface, study streams exhibited a step-like drop in macroinvertebrate community condition as indicated by a reduction in the presence of sensitive macroinvertebrate taxa. Streams with < 6% impervious surfaces contained invertebrate communities with average total richness of 33 taxa (Fall) and 31 taxa (Spring) and average EPT richness of 15 taxa (Fall) and 13 taxa (Spring). In contrast, none of the streams draining catchments with 6-27% impervious coverage exhibited average total richness > 18 taxa and average EPT richness >6 taxa. Physical habitat and water quality parameters failed to indicate the mechanism resulting in degradation of the macroinvertebrate community.

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