Ecological Indicators (Oct 2023)
Long-term evolution of groundwater hydrochemistry and its influencing factors based on self-organizing map (SOM)
Abstract
The primary water source for agricultural irrigation in the People's Victory Canal irrigation area was the Yellow River water in the early stage, and the Yellow River water diversion volume decreased in the later stage. Hence, the groundwater became the primary water source for the irrigation area. It is significant for the rational utilization of groundwater resources to explore groundwater hydrochemistry's evolution characteristics and formation mechanism. Based on the hydrochemical data of groundwater and Yellow River in the irrigation area from 1987 to 2022. The spatiotemporal evolution of chemical components of groundwater and the main influencing factors were revealed using traditional hydrochemistry research methods, self-organizing map, and stable isotopes. The results show that the classification results of groundwater and Yellow River water samples by the self-organizing map show regional and phased characteristics. Regionally, the self-organizing map classifies groundwater into five clusters, and Cluster Ⅰ–III of groundwater are mainly distributed in the head, middle and northeast areas. Cluster Ⅳ and V of groundwater are mainly distributed in the northwest region. In terms of time, from 1987 to 2001, the Yellow River water diversion volume was higher, and the ion concentration of groundwater showed a decreasing trend. The ion concentration was close to the Yellow River water ion concentration except in the northwest area. Accordingly, the classification results of the self-organizing map change from Cluster Ⅰ of groundwater to Cluster Ⅱ of groundwater. After 2001, the amount of water diverted from the Yellow River decreased, and the concentration of each ion in the groundwater at the head of the canal and the central area showed an overall increasing trend from 2001 to 2022. The classification results of the self-organizing map change to Cluster Ⅰ of groundwater. Due to the change in runoff conditions and the influence of domestic sewage, the classification results of the self-organizing map in the funnel area in the middle of the irrigation district changed to Cluster III of groundwater after 2013.
