ESTIMATION OF POLLUTANT LOADS OF NITROGEN AND PHOSPHORUS IN THE SETO INLAND SEA CONSIDERING THE CHANGE OF DOMESTIC LOADS DUE TO DEPOPULATION

Abstract

 We estimated the changes in nitrogen and phosphorus loads in the Seto Inland Sea due to depopulation, and examined the future pollution control policy in some seas. In the entire sea, the catchment population will decrease by 21.0 % in 2050 compared to 2020. As a result, the total pollutant load will decrease by 7.0 % for nitrogen and 9.5 % for phosphorus due to the decrease in domestic load. The decrease rate in the pollutant load varied from 2 % to 16 % in each sea, reflecting the composition of the load by source and the spatial distribution of the population decrease rate. With the exception of Osaka Bay and Bungo Channel, there was a relatively strong correlation between the rate of population decrease and the rate of load decrease, and the loads of nitrogen and phosphorus were estimated to decrease by 4.4 % and 2.9 %, respectively, as the catchment population decreased by 10 %. In the future, it will be necessary to consider the load reduction due to depopulation when controlling the pollutant load to achieve an abundant sea.