Field Survey on Temperature and Quality of Reservoir Water with Unstable Thermal Stratification in Bottom Layer

A field survey is carried out in order to examine water quality behaviors and thermal structure in a eutrophic reservoir, where very distinctive features are found in water quality profiles. Although temperature gradient is dynamically unstable in the bottom layer, thermal stratification has never been overturned even in a severe cold winter. On the other hand, electric conductivity is extraordinarily high in bottom layer to compensate density defect due to inverse thermal stratification. This suggests that there might be high concentration of dissolved materials and nutrients which are supposed to be originated from the reservoir bottom. In addition, dissolved oxygen is very poor in bottom layer. Based on the field survey it is investigated what kind of mechanism works to construct such a characteristic profiles of water qualities.