Groundwater quality assessment using a new integrated-weight water quality index (IWQI) and driver analysis in the Jiaokou Irrigation District, China

Abstract

Groundwater is an important water resource in arid and semi-arid regions. The impact of human activities on groundwater is increasing. After 60 years running, the groundwater quality and its formation mechanism are imperative questions needed to be answered in Jiaokou Irrigation District, Guanzhong Basin, China. In this study, the quality of groundwater in Jiaokou Irrigation District was assessed by a new integrated-weight water quality index (IWQI), and the groundwater chemistry is studied through integrated statistical, geostatistical and hydrogeochemical approaches. The patterns for the average anion and cation concentrations were HCO3− > SO42− > Cl− > NO3− > CO32− > NO2−, and Na+ > Mg2+ > Ca2+ > K+ > NH4+, respectively. Statistics showed that the major water chemistry types were HCO3-Na, SO4·Cl-Na, and Cl·SO4-Na. A new integrated-weight water quality index (IWQI) was proposed based on the entropy-weighted method and CRITIC method and showed excellent performance for explaining and evaluating the groundwater quality. The IWQI results show 65.33% of groundwater, mainly distributed in the central and western parts of this study area, was unsuitable for drinking. Furthermore, SO42－, HCO3－, Cl－, NO3－, and Na+ had more important effects on groundwater quality. The weathering process affecting groundwater quality in the study area is carbonate dissolution, followed by silicate weathering and evaporite dissolution, whereas the major geochemical processes include the dissolution and precipitation of calcite, as well as the dissolution of dolomite and gypsum (anhydrite). Cation exchange also plays an important role in the hydrogeochemical evolution of groundwater with a long residence time. Anthropogenic activities affecting groundwater quality included long-term irrigation infiltration and excessive use of fertilizers. The findings and the results of the study can improve understanding of the processes driving groundwater chemistry in Jiaokou Irrigation District, and can be used for reference to other similar regions in the world.