Effects of roadway-related physical and chemical habitat alterations on stream ecosystems.

摘要

Roadways are an important feature of both rural and urban landscapes, and disturbances associated with them have a variety of effects on stream ecosystems. Organisms may be differentially affected by toxic substances, depending on such factors as sediment and water chemistry, toxin bioavailability, uptake and elimination processes, and tolerance mechanisms. The effects of heavy metal pollution and habitat alteration related to urbanization and industry were examined along a gradient of impact in Goosefare Brook, a small stream in southern Maine with a history of water quality impairment. The structure of invertebrate assemblages changed significantly along the gradient, and were related to both chemical pollution and habitat channelization. In contrast, litter processing rates showed small decreases along the gradient of pollution related to water and sediment quality. Whole-community secondary production showed a strong decrease related to metal concentrations, from 26.4 mgAFDM/m 2/y at the reference station to 1.1 mgAFDM/m2/y at stations receiving industrial discharges. Tolerant taxa played an increasing role in community energy flow along the gradient.; Subsequently, assessment of these same parameters in five streams that cross beneath the Maine Turnpike revealed that habitat alteration related to the roadway did not exceed system resistance to stress, and negative effects of the on litter processing and invertebrate production were not evident. Litter loss rate was greater at stations downstream of the highway (−0.0024 degree-day−1) than upstream (−0.0022 degree-day −1). Invertebrate secondary production in these streams was comparable to estimates from similar streams in the coastal plain of the eastern United States (3.5 to 15.3 mgAFDM/m2/y). Significant differences in habitat, water and sediment chemistry, and biotic communities were evident among streams, although were not generally related to the presence of the roadway. Litter processing rates and secondary production were more strongly related to physical and chemical habitat variables than to the presence of the roadway. These studies have shown that pollution and habitat channelization can profoundly affect ecosystem function, and although stresses from the Maine Turnpike affect invertebrate population and community characteristics in small streams, they are not sufficient to consistently alter function in these systems.