Kunihiko Amano

Riffle topography and water flow support high invertebrate biomass in a gravel-bed river

Abstract.  We compared biomass and community structure of macroinvertebrates among 3 flow zones (deep, rapid, flat) of riffles at 3 sites in a gravel-bed river. We evaluated bed stability in these zones with a 2-dimensional hydrodynamic simulation over a range of discharge levels. Deep zones had higher flow velocity and coarser bed materials than other zones. Rapid zones were shallower with higher flow velocity than flat zones. The probability of bed movement was greatest in rapid zones and was lowest in deep zones based on bed shear stress and the size of bed materials. Total macroinvertebrate biomass was dominated by filterer insects and was highest in deep zones and lowest in rapid zones across the sites. This trend was most conspicuous for taxa that build retreats on stones, such as net-spinning caddisflies, which have a sessile life form and prefer stable environments. The trend was less apparent for taxa that move freely on the bed, such as baetid and heptageniid mayflies. The macroinvertebrate community differed between the middle and peripheral areas at deep zones. Peripheral areas were dominated more by taxa that stay under stones. The channel bed topography in deep zones of riffles is likely to support high macroinvertebrate biomass by providing greater bed stability and higher water flow, the combination of which is relatively uncommon in gravel-bed rivers.

ESTIMATION OF NITROGEN LOAD FROM AGRICULTURAL ACTIVITY IN 1920S BY USING AGRICULTURAL INFORMATION RECORDED IN PREVIOUS LITERATURES

本研究では, 複数の文献資料から農業生産活動に関する情報を詳細に分析し, 1928年, 1932年の農業由来の負荷投入量を推定した. その結果, 水田から現在の約1/10, 畑地から現在の1.4倍の負荷投入量があったことが明らかになった. 定量的な負荷投入量の推定が難しいと考えられる昭和初期でも, 過去の文献資料の記録をつなぎ合わせ, 詳細に分析することで負荷投入量推定が可能であることを示した. 同時に, 昭和初期の窒素負荷の実態, 窒素負荷が少なかった社会的背景などの結果が得られた.

EFFECTS OF HYDRAULIC CHARACTERISTICS IN FLOODS ON FISH BEHAVIOR

We tracked fish behavior using radio telemetry in experimental streams, and analyzed it with a behavior prediction model to understand the relation between fish behavior and flood flow.The results are summarized as follows. 1. Upward migration began w ith flood discharge, however, there was a threshold in flow rate for the start of the migration. 2. Experimental results were simulated successfully by a model that is driven by hydraulic characteristics such as velocity and acceleration. 3.Thus, hydraulic characteristics which can influence fish behavior seemed to be current velocity and acceleration.Upward migration of fishes during flood seems able to be explained by combining our fish behavioral prediction model and hydraulic model.