Abstract
Heat-salt double stratification was observed in a eutrophic reservoir in which hypolimnion shows high electric conductivity and has an inverse temperature gradient. The hypolimnic water is so heavy and stable that the reservoir water has never been overturned in full-depth-scale even in mid-winter. Based on an in-situ measurement of water quality it was discussed how the heat-salt density system was constructed and related to reservoir eutrophication. The field data showed that release of dissolved materials from sediments produces salty and heavy water mass which generates an inclined plume along the bed slope of reservoir. The plume plays a major role in transporting heat and dissolved components of metals, nutrients and organic matters from the anaerobic metalimnion into the hypolimnion. This is how a relatively warm and heavy water mass with an inverse temperature gradient is concentrated there. This is new eutrophication mechanism that has to be taken into consideration in an analysis of reservoir water quality.
