CHANGES IN WATER AND MATERIAL DYNAMICS IN THE YODO RIVER BASIN DUE TO DEPOPULATION

Abstract

 We developed a method for estimating the amount of water and material transport in the Yodo River Basin, and estimated the future changes due to population decline. In addition, a quantitative analysis of water and material dynamics in the basin and its impact on the inflow load to Osaka Bay was conducted. The results showed that the discharge of nitrogen and phosphorus from sewage treatment plants will decrease by 25.1 % and 20.6 %, respectively, in 2050, while the discharge of silicon will decrease by only 8.9 %, reflecting the differences in their addition and removal characteristics in the artificial water cycle system. The total loadings of nitrogen, phosphorus and silicon into the sea will decrease by 14.7 %, 7.8 % and 1.5 %, respectively, due to population decline in 2050. This suggests that the inflow loadings of nitrogen and phosphorus will be substantially reduced in the future without the need to promote the reduction of inflow loadings from land. It is estimated that although primary production will decrease in the inner part of the bay due to a relative decrease in nitrogen and increase in silicon in the future, it is unlikely that the dominant species will change from diatoms.