A STUDY ON THE VERTICAL DISTRIBUTION OF PHOSPHORUS IN DAM RESERVOIRS

Abstract

 In this study, we investigated the characteristics of vertical distribution of phosphorus in five dam reservoirs in western Japan, under the anoxic condition of bottom waters. As a result, a vertical distribution pattern was sometimes confirmed in which the phosphorus in the bottom layer was relatively smaller than that in the middle layer in all reservoirs. In addition, the observational results in the Tsuruda Dam reservoir suggested that such vertical distribution might be triggered by the elution of phosphorus and Fe²⁺ from the sediment and their resuspension near the bottom. It was also confirmed that released phosphorus from bottom sediments was rarely observed in the Tsuruta Dam reservoir. The main factors behind these results were considered to be due to the relatively high supply of nitrate from upstream and the low amount of labile organic matter in the sedimentary mud, which made it easier to maintain a relatively oxidative environment in the bottom layer and could suppress and delay the phosphorus release from sediment.