Comparison of Macroinvertebrate Community Structures between Artificial Environments and Natural Streambeds in Mountain Streams

Abstract

In mountain streams, artificial structures like restoration dams and culverts help maintain forests, roads, and streams. However, while their negative impact on aquatic ecosystem is known in lower river reaches, their effects in mountain streams are less understood. To assess this, we compared benthic macroinvertebrate communities in natural and artificial streambeds in the Ishite River headwaters, Ehime, Japan. We studied benthic macroinvertebrates in pools, riffles, and rapids in natural streambeds and in culverts, dam walls, open ditches, a levee crown and a sedimentary zone associated with a mountain restoration dam. Results demonstrate that benthic macroinvertebrate community densities, taxon richness, and diversity tended to be greater in the natural streambeds than in the artificial environments. In all but the culverts, ordination using non-metric multidimensional scaling revealed that the benthic macroinvertebrate community structure of the natural streambeds and the artificial environments were characterized by their type. For the culverts, the community composition varied among sampling sites. For the dam walls, it was characterized by relatively small taxa such as Chironomidae and Diamesinae. Unlike all other sampling sites, the sedimentary zone tended to show lentic taxa. For the open ditches, the diversity and density were similar to that of natural streambeds. However, the results for the sedimentary zone and open ditches should be interpreted with caution due to the small number of sites examined. The results of this study indicate that the benthic macroinvertebrate communities in artificial environments in mountain streams differ in composition from those in natural streambeds, although the species present are not substantially different.