[A-HW18] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW18-P07] Estimate of Annual Total Phosphorus Loading from Yodo River Catchment during 1940s~2010s

*Kunyang Wang¹, Shin-ichi Onodera¹, Mitsuyo Saito¹ (1.Graduate School of Advanced Science and Engineering, Hiroshima University)

Keywords:Osaka Bay, phosphorus discharge, non-point source pollution, wastewater treatment, Soil & Water Assessment Tool

The global urban population in 2020 was four times that in 1960. Rapid population growth has led to an increase in point source pollution represented by domestic and industrial wastewater, causing serious environment pollution. At the same time, due to the increase in food demand due to population growth, chemical fertilizers are widely used in agricultural production to increase yields, of which phosphorus is a major nutrient. However, excessive nutrient levels in the field due to fertilizer overuse cannot be completely absorbed by plants, and a considerable quantity of phosphorus is transported in water, which enriches water bodies downstream, causing eutrophication. This affects not only river ecology, but even marine ecosystems. Osaka Bay is a part of the Seto Inland Sea, but it shows the worst water quality in this sea. There have two large rivers connected to Osaka Bay, Yamato River and Yodo River, which catchment covers an area of 1077 km² and 8240km², respectively. Two rivers straddling six prefectures, Osaka, Nara, Kyoto, Shiga, Mie, and Hyogo, have very important geographic and economic value for Kansai region.
This work extends an existing phosphorus transfer and budget model of Yamato River catchment which built by Soil & Water Assessment Tool, to estimate phosphorus loading of Yodo River catchment during 1940s~2010s. Results show that the total phosphorus loading in the Yodo River catchment peaked in 1965 at 6843 tons owing to untreated wastewater discharge and rapid increase in population growth. The total phosphorus load from the two rivers also reached the peak in 1965 at 7847 tons. After this, the phosphorus load begins to decrease. In the 2010s, the phosphorus load from the Yodo River and the total load from the two rivers are 1881 and 2295 tons/yr respectively.

Acknowledgment: Acknowledgment: This research has been supported the Asia-Pacific Network for Global Change Research (APN) under Grant No. CRRP2019-09MY-Onodera (funder ID: http://dx.doi.org/10.13039/100005536), Grant for Environmental Rehabilitation and Creation of the Osaka Bay Area (PI: Mitsuyo Saito, Grant Number: 040006, 2022). And Grant-in-Aid for Scientific Research (A) by Japan Society for the Promotion of Science (Project No. 21KK0192, PI: Shin-ichi Onodera).