Relationship between stonefly assemblages and riparian environment: case study in mountain stream in Japan

摘要

Stream width, instream litter, and substrate conditions differ depending on the location along the stream and the season. Leaves in the upper stream riparian forest fall directly into the stream, become litter, and are broken down according to stream flow (VANNOTE et al. 1980, SWEENEY 1992, CHERGUI & PATTEE 1993, JOINSON & COVICH 1997). Input of detritus from riparian forest is essential for the conservation or restoration of many of the food webs in streams (WALLACE et al. 1997). Ben-thic invertebrate assemblages also differ depending on the lo-cation along the stream and the season. Abundance of shred-ding invertebrates decreases and that of scrapers and grazers increases according to stream flow (VANNOTE et al. 1980, MIN-SHALL et al. 1985, REED et al. 1994). The quantity and quality of riparian vegetation along streams affects instream alkalinity (KRUEGER & WATERS 1983), and the quality of nutrients in streams derived from riparian land influences larval growth (FIANCE 1978, MALLEY 1980, HAWKINS et al. 1982, RODGERS 1984). Water quality and assemblage of benthic invertebrate would be affected by surrounding land use. An understanding of variation in riparian landscapes may lead to a better interpretation of aquatic insect life cycles (REED et al. 1994, RICHARDS et al. 1996). Among typical aquatic insect groups of temperate regions (stoneflies, mayflies, and caddisflies), stoneflies tend to occu-py the cooler bodies of freshwater such as those in mountain-ous regions in western Japan. Additionally, most of the stone-flies are shredders or predators that are more abundant in the upper reaches. When the existence of stoneflies is strongly re-lated with the riparian landscape, stonefly assemblages might be different, depending on the surrounding land use, even in the upper reaches.