An Experimental Study on Deposition of Fine Particulate Organic Matter affected by River Channel Morphology

Abstract

河川地形が微粒状有機物の堆積に与える影響を調べるため, 浮遊型/沈降型の二タイプのマツ花粉をトレーサーとして, 堰上流にダム型淵(湛水域)が形成されている水路床と, 交互砂州の発達し河床近傍の流れが蛇行する水路床で水理実験を実施した。その結果, ダム型淵においては沈降型の堆積が卓越した。交互砂州においては, 砂州域に沈降型と浮遊型の両方の堆積密度が高い現象が見出された。また, 流心線沿いの河床には沈降型がより多く堆積することがわかった。それらの結果は比重の異なる微粒状有機物の河床堆積様式と対応していると考えられる。

We investigated the spatial distribution of FPOM and its relation to geomorphic features such as damming pool and alternate bar structures by conducting a series of experiment on FPOM deposition using two types of pine pollen as analogue. Then we examined relations of deposition density of both floating pollen(ρdep-F), and sinking pollen(ρdep-S) to lateral elevation difference (∆z) and surface flow velocity (us). In damming pool structure, ρdep-S was higher than ρdep-F and was negatively correlated with us. While, in alternate bar structure, ρdep-S showed no difference from ρdep-F, and was negatively correlated with us and ∆z. These results indicate FPOM in stream may be differently distributed by its source origin and geomorphic features through specific deposition process even in reach scale distance. Advantages of pine pollen as FPOM analogue for evaluating dam impact on river ecosystem were also discussed.