Abstract
To estimate the manganese source in a dam reservoir and factors affecting manganese release from bottom materials, water and sediment qualities were investigated in the Ryorigawa Dam, which showed a significant increase in manganese concentration in its hypolimnion during the stratified period. In the bottom layer of the water column, the concentration of dissolved manganese correlated with that of dissolved calcium compared with other metals except iron. From the manganese distribution in the water column and manganese content of the sediment, it was estimated that the manganese source in the hypolimnion consisted of not only sediment but also rock or groundwater. Furthermore, the release of metals from bottom materials including rocks and sediment was studied in the laboratory. The releases of Mn from sediment and rock under anoxic condition were found to be promoted by its coexistence with soluble Ca and Fe(II), respectively.
