Physical characteristics and macroinvertebrate biomass of riffles in the Toyo River, Aichi Prefecture

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  • 愛知県豊川における瀬の物理特性と底生動物現存量
  • アイチケン トヨカワ ニ オケル セ ノ ブツリ トクセイ ト テイセイ ドウブツ ゲンソンリョウ

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Abstract

To better understand the relationships between the physical characteristics and macroinvertebrate biomass of riffles, macroinvertebrate communities were surveyed for four seasons at 14 sites along the Toyo River in Aichi Prefecture, and comparisons were made among different river segments (lowland, canyon, upland, and mountain). The size of main bed material was greater in the upland and mountain segments, whereas the immobility index of bed materials (the ratio of main material size to movable material size during an annual flood) was greater in the lowland segment. Mean flow velocity tended to be greater in the canyon and upland segments. Mean total macroinvertebrate biomass was greatest in the lowland segment (1.7-2.5 greater than in the canyon and mountain segments), followed by the upland segments. At most sites, the total macroinvertebrate biomass was largely dominated by grazers and filterers, with the biomass of these groups tending to be greater in the lowland segment. On the other hand, the biomass of predators was greater in the upland and mountain segments. Macroinvertebrates were further classified into bed-residence types according to their requirements or ability to utilize interstices of stones/sand and their mobility (free living or holding retreats/cases). Instances of dominant types in the lowland segment included surface-retreat, interior-retreat, and interior-free types, which are assumed to prefer a stable environment. On the other hand, dominant types in the upland segment were the inter-stones retreat and inter-stones free types, which are assumed to require moderate-sized interstices between stones. Based on the correspondences between physical characteristics and dominant bed-residence types in these riffles, the main physical characteristic that contributed to the greater macroinvertebrate biomass appears to be streambed stability in the lowland segment, whereas in the upland segment it appears to be the availability of interstices associated with larger bed materials.

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