UC Santa Barbara

The Western Jianghan Plain (WJHP) lies in the middle reaches of the Yangtze River. It has been impacted by anthropogenic activities during the past decades. The long-term variations of the WJHP's regional aquifer's hydrochemistry and groundwater quality have not been previously assessed. Sixteen physiochemical parameters at 29 monitoring wells within the Western Jianghan Plain were monitored during 1992-2010 and analyzed with multiple approaches. The confined groundwater is predominantly of the HCO₃-Ca-Mg type with Cl^-, SO₄^2-, NH₄-N, and NO₃-N showing remarkable spatial variations. Correlation analysis was used to identify the origins and contamination sources of groundwater. The seasonal Mann-Kendall test revealed that pH, NO₃-N, and Cl^- concentrations at 27, 26 and 15 wells, respectively, exhibited significant increasing trends during 1992-2010. The increase of pH may be attributed to CO₂ degassing caused by extensive groundwater extraction. Regional average NO₃-N concentrations of groundwater increased coincidently with the increased use of fertilizer, which suggests that nitrate pollution is caused by agricultural activities. Abnormally high values of Cl^- and SO₄^2- at some wells were induced by industrial chemicals. In addition, the similarity of the temporal variations of the regional average of pH, NH₄-N, and NO₃-N concentrations in groundwater with those in the Yangtze River at the outlet of the Three Gorges Reservoir (TGR) suggests that the variations of these parameters in the WJHP is partly due to water storage by the TGR. This study presents an analysis of temporal variations of groundwater quality in the WJHP that reveals a relation between the creation of the TGR and downstream groundwater quality. This paper's findings provide clues for measures that could be taken to protect the groundwater quality of the WJHP's aquifer.