报告主题：Hydrogeochemistry of Aquitard-Aquifer System in Pearl River Delta, China

主讲人：焦赳赳教授（香港大学）

主持人：李猛教授

时 间：2024年8月21日周三15：00

地 点：深圳大学致知楼706

嘉宾简介：

Dr Jimmy Jiao is a professor in Hydrogeology at the Department of Earth Sciences, the University of Hong Kong. He obtained his BEng and MEng in Hydrogeology from China University of Geosciences (Wuhan) and PhD in Civil Engineering from the University of Birmingham, UK. He worked as Associate Editor (2002-2008) for Ground Water and Editor (2008-2015) of Hydrogeology Journal and. He was the 2023 recipient of O.E. Meinzer Award, the Hydrogeology Division, Geological Society of America and the M King Hubbert Award of National Ground Water Association. Dr Jiao was elected Fellow of the Geological Society of London, the Geological Society of America, and the American Society of Civil Engineers. He has published over 230 SCI journal papers and a book on Coastal Hydrogeology.

报告摘要：

This presentation summarizes the results of a comprehensive study on the hydrogeology and geochemistry of the aquifer-aquitard system in the Pearl River Delta (PRD) in China since 2007. The study aimed to gain a deeper understanding of the generation and migration of salinity, ammonium, and arsenic in the aquitard-aquifer system. The study found that the PRD is dominated by two thick layers of aquitards of mainly marine origin rich in organic materials, and below that is an areally extensive basal aquifer. Unlike previous studies that focused mainly on the aquifer, this study treated the aquitard-aquifer system as a hydrogeochemical continuum. Regional groundwater flow is very stagnant due to clay-rich aquitard materials and gentle topography. The system is under an extreme reducing environment, and the aquitard has a high content of organic matter. The high salinity is caused by the palaeo seawater intrusion in the Holocene.

A total of 40 boreholes were drilled to take core samples of the aquitard, and groundwater samples were collected from the basal aquifer. Two key sites were equipped with nested multi-level piezometers to provide long-term monitoring information on the water level and geochemistry. The core samples were used for extraction of pore water for centrifugation and bulk chemical analyses in the laboratory. The study found that ammonium occurred at concentrations up to 390 mg/L in the basal sand Pleistocene aquifer 20-50 m deep. This ammonium was natural, areally extensive (1600 km2), and originated from the decomposition of organic-rich materials due to various microbiological processes in the overlying Holocene-Pleistocene aquitard. It entered the aquifer by groundwater transport and diffusion. The arsenic with a concentration up to 161 ug/L in the aquifer is also associated with the organic matters. The regional fault zones and palaeo-river channels at the early stage of Holocene control the deposition environments and subsequently the overall spatial distributions of geochemistry in the aquifer-aquitard system. This research provides valuable insights into the complex hydrogeology and geochemistry of the aquifer-aquitard system in PRD and lays the foundation for future studies aimed at improving our understanding of this important system.