Longitudinal Variations in Macroinvertebrate and Periphyton Communities in a Mountain Stream Receiving Mine Drainage: Are Their Changes in Response to Metal Contamination Different?

We investigated longitudinal variations in metal concentrations and in benthic macroinvertebrate and periphyton communities at 13 sites in the tributaries of the upstream Hida River to assess the ecological impacts of mine drainage. At the sites immediately downstream of the inflow of mine drainage, the concentrations of trace metals such as zinc increased （ e.g., the maximum zinc concentration of 0.94 mg L -1 was observed ） , large reductions in the taxon richness and abundance of macroinvertebrates and in the taxon richness of periphyton were observed, and tolerant taxa （ e.g., chironomids and baetid mayflies, and Achnanthidium diatoms ） , which are known to be present in metal-contaminated rivers, dominated their respective communities. Metal concentrations decreased at the downstream sites, and the macroinvertebrate community composition observed at the most downstream site was similar to those at reference sites. Although the longitudinal variations in the taxon richness and community composition of macroinvertebrates and periphyton were similar in the studied river, we observed some differences such as the markedly increased abundance of periphyton at the sites downstream of the inflow of mine discharge. Thus, the investigaton of multiple biological groups is required for a comprehensive understanding of the ecological impacts of mine drainage on aquatic communities.