Submarine groundwater discharge and associated nutrient fluxes in the Greater Bay Area, China revealed by radium and stable isotopes  

作　　者：Qianqian Wang Xuejing Wang Kai Xiao Yan Zhang Manhua Luo Chunmiao Zheng Hailong Li 

机构地区：[1]State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control,School of Environmental Science and Engineering,Southern University of Science and Technology,Shenzhen,Guangdong 518055,China [2]School of Environmental Science and Engineering,Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control,Southern University of Science and Technology,Shenzhen,Guangdong 518055,China [3]MOE Key Laboratory of Groundwater Circulation&Environment Evolution and School of Water Resources and Environment,China University of Geosciences(Beijing),Beijing 100083,China

出　　处：《Geoscience Frontiers》2021年第5期397-410,共14页地学前缘（英文版）

基　　金：supported by the National Natural Science Foundations of China(Nos.41890852,42077173);the Shenzhen Science and Technology Innovation Committee(No.JCYJ20190809142417287);State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control.

摘　　要：The estuary-bay system is a common and complex coastal environment.However,quantifying submarine groundwater discharge(SGD)and associated nutrient fluxes in the complex coastal environment is challenging due to more dynamic and complicated riverine discharge,ocean processes and human activities.In this study,SGD and SFGD(submarine fresh groundwater discharge)fluxes were evaluated by combining stable and radium isotopes in the Guangdong-Hong Kong-Macao Greater Bay Area(GBA),a typical estuary-bay system.We first built a spatially distributed radium mass balance model to quantify SGD fluxes in coastal areas of GBA integrating the Pearl River Estuary(PRE),bays and shelf.We then used the stable water isotope(d2 H and d18O)end-member mixing model to distinguish submarine fresh groundwater discharge(SFGD)from SGD.Based on the 228Ra mass balance,the estimated SGD fluxes in the PRE,adjacent bay,and shelf areas were(6.14±2.74)×10^(8) m^(3) d^(-1),(3.00±1.11)×10^(7) m^(3) d^(-1),and(5.00±5.64)×10^(8) m^(3) d^(-1),respectively.Results showed that the largest area-averaged SGD was in the PRE,followed by that in the adjacent shelf and the bay.These differences may be mainly influenced by ocean forces,urbanization and benthic topographies controlling the variability of groundwater pathways.Further,the three end-member mixing model of ^(228)Ra and salinity was developed to confirm the validity of the estimated SGD using the Ra mass balance model.In the two models,groundwater endmember and water apparent age estimation were the main sources of uncertainty in SGD.The estimated SFGD flux was(1.39±0.76)108 m^(3) d^(-1),which accounted for approximately 12%of the total SGD.Combining stable and radium isotopes was a useful method to estimate groundwater discharge.Moreover,the estimated SGD associated dissolved inorganic nitrogen(DIN)flux was one order of magnitude higher than other DIN sources.SGD was considered to be a significant contributor to the DIN loading to the GBA.The findings of this study are expected to provide valu

关 键 词：Radium isotopes Stable isotopes Submarine fresh groundwater discharge NUTRIENTS Coastal aquifers Pearl River estuary 

分 类 号：P731[天文地球—海洋科学] X523[环境科学与工程—环境工程]