11:00 〜 13:00
[AHW24-P20] Spatiotemporal Characteristics and Sources of Riverine Nitrogen in Typical Urbanized Areas in the Guangdong-Hong Kong-Macao Greater Bay Area
キーワード：typical urbanization area, nitrogen, isotope trace, source identification
A typical urbanized area in the Guangdong-Hong Kong-Macao Greater Bay Area, Liuxi River-West Channel-North Channel in Guangzhou City, was used to reveal the impacts of rapid urbanization on riverine nutrients. With water quality data collected since the 1980s, nitrogen was found to be the major nutrient pollution in the study area, and water environment could be separated into several periods, i.e., pollution intensified in the 1980s, obvious fluctuation in the 1990s, gradual improvement in the beginning of the 21st century.. To further study the spatiotemporal characteristics and sources of river nitrogen, two field campaigns were implemented in both wet and dry season, e.g. July 2020 and January 2021. Forty surface water samples were collected to analyze indicators such as major ions and stable isotopes (δ15N-NO3-, δ18O-NO3- and δ15N-NH4+) The spatiotemporal characteristics and sources of river nitrogen in the study area were explored by using hydrochemistry and isotopes (δ15N-NO3-, δ18O-NO3- and δ15N-NH4+) methods. The results show that from upstream to downstream, the influences of human activties on the mass concentrations of Cl-, NH4+-N, NO3--N, DIN (dissolved inorganic nitrogen) are gradually prominent. The concentrations of NH4+-N and DIN in the wet season are higher than those in the dry season, mainly due to the the more intensive influence of exogenous input than the combined effect of rainfall and upstream water dilution. In the composition distribution of dissolved total nitrogen, NH4+-N and NO3--N are the main forms in the wet and dry season respectively, indicating significant impact of human activities in the wet season. There is a strong positive correlation between NH4+-N and Cl- concentration in the wet season, indicating that NH4+-N and Cl- may have similar or the same sources in the wet season. Results of ion ratio of Na/Cl and stable isotope tracing are highly consistent. This indicates that upstream farmland chemical fertilizer, soil organic nitrogen and aquaculture sewage are the main sources of nitrogen in the upstream, while the soil organic nitrogen and urban sewage are the main sources of nitrogen in the downstream. The research results can provide data support and theoretical basis for river water environment protection and water resources management in the study area.