Abstract:

The Hexi area is the main emergency groundwater source for Xiangtan City, Hunan Province, ensuring the urban water supply safety demand. Identifying the spatio-temporal evolution process of water supply hydrochemical components under the long-term influence of climate change and human activities has important practical guiding significance for the local development and utilization of groundwater resources and pollution control. In order to quantitatively reveal the evolution processes of karst hydrochemistry under long-term controls of precipitation and human activities, as well as the spatio-temporal distribution and evolution patterns of hydrogeochemical characteristics in the karst areas of Southern China, this study applies multivariate statistical analysis, geostatistical analysis, hydrochemical methods，and Piper diagrams, Gibbs models, and major ion ratios to analyze the spatio-temporal variation patterns and influencing factors of karst hydrochemistry in the study area, based on national groundwater quality monitoring data (2002—2021). The results show that: The karst hydrochemistry in the study area exhibits horizontal zonation in space, which can be divided into Hydrochemical Zone Ⅰ and Hydrochemical Zone Ⅱ. Along the overall flow direction of karst water from Zone Ⅰ to Zone Ⅱ, the hydrochemical components show a “positive increase”. The concentration of karst water chemical components has shown a phased change on the annual time scale over the past 20 years, with the overall evolution process being “stationary-rising-declining-stationary”. The key time nodes are 2007, 2011, and 2017. The spatial differences in karst hydrochemistry are mainly influenced by human activities. On the one hand, agricultural non-point source pollution and urban domestic sewage enter the aquifer through surface infiltration, increasing the concentration of some components in Zone Ⅱ; On the other hand, artificial groundwater exploitation alters the local karst water flow field, causing hydrochemical components within the study area to exhibit “reverse change” characteristics along the overall flow direction of karst water. The evolution process of karst hydrochemistry on the annual time scale is influenced by changes in annual precipitation, and the influence time can be traced back to 2-3 years ago. This study comprehensively applied mathematical and chemical methods to quantitatively reveal the evolution process of karst hydrochemistry under the long-term control of precipitation conditions and human activities, which can provide reference for analyzing the spatio-temporal distribution and evolution law of hydrogeochemistry in karst areas of Southern China.

Key words: emergency groundwater source')">

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