Chemical And Isotopic Response To Intensive Groundwater Exploitation And Its Implications

The stress imposed on the available water resources due to man’s impact (exploitation, release of pollutants and agricultural and industrial practices) has resulted in depletion of the available reserves as well as deterioration of water quality in many parts of the world. Over wide areas, abstractions are exceeding current natural recharge and these water resources are being mined, especially in arid and semi-arid areas. Sustainable development and effective management of those water resources needs long term monitoring records to understand the changes and dynamic responses due to the exploitation. In this dissertation, taking Shijiazhuang piedmont plain as a case study, the response of groundwater systems to intensive exploitation and groundwater availability were assessed by the combined use of conventional hydrochemical data and environmental isotopes. The following conclusion are suggested from the present study.1. This system has experienced intensive groundwater abstraction during the last50years to supply increasing water demand, agricultural and industrial needs, which has caused a continuous groundwater level decline (up to45m). The abstraction rate once reached to40×107m3/a in the urban.2. High aquifer vulnerability was implied by the generally increasing concentration of TDS, major cation and anion of groundwater, and the changes of groundwater renewal rate estimated by tritium and Hydrological Response Curve (HRC) calculated simple dynamics model in the past40years. Those changes also suggested that a short turn over time was induced by intensive groundwater exploitation;3. The enrichment trend of δ18O and82H value with groundwater abstraction, suggested the impacts of local recharge from irrigation return and a modification of the groundwater flow in the aquifers was caused. The changes of HRC with aquifers exploited also suggested the impacts of local recharge from irrigation return. The different evolution groundwater renewal rate between inside (increased) and outside (reduced first then increased) the depression cone, further proved that the groundwater system could be impacted by agricultural irrigation.4. The vertical distribution of tritium in aquifers showed that the active groundwater recharge zone has been extended form the depth of100m to～150m since1985, indicating an enhancement of active groundwater flushing of local groundwater system due to intensive groundwater abstraction.The results show that stable isotopes, radioactive isotopes and the major hydrochemical ions are excellent tools for characterizing and understanding aquifer systems that are undergoing long term intensive exploitation. The establishment of methodologies for monitoring and predicting changes in water quality and quantity that will lead to improved water resources management and developed for effective management strategies.