Chemical and Isotopic Responses to Intensive Groundwater Abstraction and Its Implications on Aquifer Sustainability in Shijiazhuang,China

The stress imposed on groundwater resources due to intensively exploited aquifer has resulted in groundwater depletion in the North China Plain（NCP）. Management of groundwater resources needs to understand the changes or dynamic responses due to the exploitation. The response of groundwater systems to intensive exploitation and groundwater availability were assessed by the combined use of conventional hydrochemical data and environmental isotopes in Shijiazhuang, NCP. The generally increased concentration of total dissolved solids（TDS）, major cation and anion of groundwater in the past 40 years indicated high vulnerability of aquifer system but a short turn over time by intensive groundwater exploitation, which also was proved by changes of groundwater renewal rate estimated by tritium. The vertical distribution of tritium in aquifers showed that the active groundwater recharge zone has been extended from the depth of 100 to ~150 m since 1985, indicating an enhancement of active groundwater flushing of local groundwater system due to intensive groundwater abstraction. The enrichment trend of δ^（18）O and δ~2H value with groundwater abstraction, suggested the impacts of local recharge from irrigation return. The increase concentrations of nitrate with time indicated high aquifer vulnerability. A comprehensive effort should be developed for effective management strategies that ensure long-term, stable, and flexible water supplies to meet water demands in the NCP.

Potential for natural and enhanced attenuation of sulphanilamide in a contaminated chalk aquifer

Understanding antibiotic biodegradation is important to the appreciation of their fate and removal from the environment. In this research an Isotope Ratio Mass Spectrometry（IRMS）method was developed to evaluate the extent of biodegradation of the antibiotic,sulphanilamide, in contaminated groundwater. Results indicted an enrichment in δ^（13）C of8.44‰ from-26.56（at the contaminant source） to-18.12‰（300 m downfield of the source）.These results confirm reductions in sulphanilamide concentrations（from 650 to 10 mg/L）across the contaminant plume to be attributable to biodegradation（56%） vs. other natural attenuation processes, such as dilution or dispersion（42%）. To understand the controls on sulphanilamide degradation ex-situ microcosms assessed the influence of sulphanilamide concentration, redox conditions and an alternative carbon source. Results indicated, high levels of anaerobic capacity（~50% mineralisation） to degrade sulphanilamide under high（263 mg/L）, moderate（10 mg/L） and low（0.02 mg/L） substrate concentrations. The addition of electron acceptors; nitrate and sulphate, did not significantly enhance the capacity of the groundwater to anaerobically biodegrade sulphanilamide. Interestingly, where alternative carbon sources were present, the addition of nitrate and sulphate inhibited sulphanilamide biodegradation. These results suggest, under in-situ conditions, when a preferential carbon source was available for biodegradation, sulphanilamide could be acting as a nitrogen and/or sulphur source. These findings are important as they highlight sulphanilamide being used as a carbon and a putative nitrogen and sulphur source, under prevailing iron reducing conditions.