Author(s): Kohji Michioku; Tohru Kanda

Linked Author(s): Kohji Michioku

Keywords:

Abstract: A reservoir investigated is seriously eutrophicated and shows a stable doubledensity stratification of heat and salt. The bottom layer is highly contaminated with dissolved nutrients and ionic metals, which brings significant salinity there. The impounded water has never been overturned over the years because of its heavy bottom water. Another characteristic feature is that an inverse temperature gradient is kept in the bottom layer throughout whole year. The resultant temperature and salinity fields show a complicated double-density structure. A field measurement was carried out in order to examine how heat-salt convection is involved in the bottom water eutrophication. The field data suggest the following hydrodynamics. Heavy water mass with high salinity is produced along the reservoir bed by anaerobic reduction of sediments. The heavy water with high concentration of nutrients, ionic metals and other dissolved materials then gravitationally goes down the bed slope, in other words, inclined plumes are generated along the sloping reservoir terrain. The plumes transport not only salinity but also heat from the warm upper layer. This could be a major mechanism of heat-salinity integration in the reservoir bottom. Water quality troubles due to the bottom water eutrophication could be minimized if some technical countermeasures would be devised for controlling the heat-salt convection.

DOI:

Year: 1999