Insights of the change characteristics of groundwater in ecological water replenishment area: A case of lower reach of the Yongding river, China

Assessing the characteristics of groundwater variations in areas affected by artificial recharge is essential for guiding the groundwater resources management and groundwater ecology. However, it is still a challenging task for characterizing the groundwater variations when monitoring data are limited or short-term. To this end, this study applied methods including wavelet analysis, correlation analysis, statistical methods, principal component analysis (PCA) and self-organizing maps (SOM), to provide an initial assessment of the characteristics of groundwater variations following artificial recharge in Langfang, China. The groundwater level analysis results indicated that high-intensity water replenishment significantly contributed to the rise of groundwater level, especially in areas along the river. Wavelet analysis revealed notable lag times in groundwater response to recharge sources along the river, which has important implications for selecting appropriate monitoring periods when assessing the potential effects of artificial recharge on groundwater hydrochemistry. Statistical analysis, PCA, and SOM clustering further suggested that the infiltration of water replenishment along the river channel enhances the dilution effect on groundwater. This leads to a reduction in the average concentrations of chemical components such as TDS and total hardness, which can facilitate the recovery of microbial activity and ecological functions. However, the results also highlighted a possible phenomenon of increase in ammonia nitrogen concentrations occurring in the context of ecological water replenishment, which may imply a potential ecological risk for groundwater fauna. These findings improve understanding of groundwater variations under artificial recharge and provide valuable support for groundwater resource management and groundwater ecology protection.