[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-P23] Water environment issues in Chinese megacity delta-Sewage impacts on Peral river coastal area

*Guangzhe Jin¹, Shin-ichi Onodera², Mitsuyo Saito³, Yuta Shimizu⁴, Jianyao Chen⁵ (1.College of Ocean and Meteorology, Guangdong Ocean University , 2.Graduate School of Integrated and Arts Sciences, Hiroshima Universityl , 3.Graduate school of Environmental and Life Science, Okayama University, 4.Western Region Agricultural Research Center, National Agriculture and Food Research Organization., 5.The School of Geography and Planning, Sun Yat-sen University )

Keywords:Sewage, Peral River Delta, Megacity, Sediment, Nutrient

The Pearl River Delta (PRD) is one of the most developed regions in China. It contains seven major cities and will grow into a single mega metropolitan area. The PRD includes a population of over 140 million within an area of 39,380 km2. As a result, estuaries in PRD often suffer from water pollution due to growing populations, urbanization, and industrialization.
The main water environment problem in PRD is a rapid increase in water resources demand with relatively low water efficiency, increasing saltwater intrusion, coastal environment problems due to water pollution. The water resource demand type has changed from agriculture to industry with an annual rate of 2.39% until 2015, but with much higher water consumption per unit of GDP than Japan. Estuaries in PRD suffer from multiple contaminants with high nutrient discharging fluxes due to extensive water discharging quantities of the Peral river. With efforts regulating the water quality in PRD, Sever water (Classification higher than 3 of the environmental quality standards) still comprise over 1/3 of the whole water bodies. Results of a field survey in 2017 show high nutrient contents in water and high phosphorus(P) contents (highest of 4000ug/g.DW), and high releasing potential(approx. 50% is mobile P) in the Peral river, indicating a larger sediment P pool with higher mobility than in the Osaka Bay. Our results based on nitrate isotope analysis showed local cities and diluted Peral River water influenced the nitrate dynamics in the coastal area from western Guangdong province, nitrate isotope analysis the dominant nitrate sources is originating from manure and sewage.