Study on Characteristics of Flow and Primary Production of Riffles and Gravel Rivers

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Field observations on the characteristics of primary production of periphyton were performed at riffles and pools in Tama-river. The imitated gravels made of concrete were settled in the riffles and the pools. Three imitated gravels were picked out at each location every week for 55 days, and the periphyton attached to them was removed by toothbrush. The amount of chlorophyll-a of the algae was measured by using spectrophotometer. It was found that the periphyton growing on the gravels at riffles has larger photosynthetic activity than that at pools.The laboratory measurements on the growth of periphyton were conducted in 4 tandemly placed laboratory flumes, in which the environmental conditions except for the hydraulic conditions were controlled to be the same among the flumes in order to identify the effects of hydraulic characteristics on the primary production of periphyton. The results of the experiments indicate that the primary production of periphyton takes large value for the case where the near-bottom turbulence is large.A numerical simulation model was presented to describe the temporal growth of periphyton. The effect of the hydraulic conditions on the growth of periphyton is taken into account in the model via the diffusivity of nutrients and other substrates inside of the biofilm. The computation predicts the temporal variation of the biomass of periphyton in the experiments well.