4.3.1. Groundwater Chemistry Control Mechanisms

A Gibbs plot can be used to illustrate the causal mechanism of water chemical composition [41]. In the Gibbs plot, if the TDS value is high and the Na+/(Na++Ca2+) or Cl−/(Cl−+HCO3 −) ratio is close to 1, the ion control mechanism is evaporative crystallization. If the TDS value is medium and the Na+/(Na++Ca2+) or Cl−/(Cl−+HCO3 −) ratio is less than 0.5, the ion control mechanism is water rock effect. If TDS value is low and the Na+/(Na++Ca2+) or Cl−/(Cl−+HCO3 −) ratio is close to 1, the water chemistry component control mechanism is the rainfall effect [42,43]. From the Figure 6, it can be seen that the chemical composition of groundwater in the study area is mainly dominated by water–rock action.

**Figure 6.** Gibbs diagrams showing the groundwater chemistry controlling mechanisms.
