WATER TEMPERATURE VARIATION AND PRIMARY PRODUCTIVITY AT DOWNS1REAM REACH OF THEYAHAGI RIVER

Abstract

The active uptake of river water for the water utilization in the Yahagi River has decreased the river discharge, which might affect the water temperature and the river ecosystem. In the present study, the effects of the water uptake on water temperature and primary productivity of periphyton were investigated at the downstream reach of the Yahagi River by field observations and numerical simulations. The results of the field observation shows that the thermal conduction from river water to river bed was much smaller than the net radiation, and therefore the temporal and spatial variations of river water temperature were mainly induced by the heat exchange between air and water. The computational results show that the increase of the river discharge reduced the spatial and the temporal variations of water temperature through the change of heat capacity of river water, and the primary productivity of periphyton decreased with river discharge.