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To confirm quantitative relationships, as mentioned above, correlation coefficients between reference vectors for each parameter were calculated (Table 2). There is a high correlation (r = 0.99) between Cl and NO3. There is also a high correlation between Na+ and Mg2+ (r = 0.92). Similarly, the color gradient for the relationship between SO42– and Ca2+ indicates a high correlation coefficient (r = 0.94). The relation between each ion indicates factors affecting groundwater chemistry. For example, a high co-variation (R2 = 0.72) between higher concentrations of NO3 and Cl was observed, indicating that they originate from common sources, such as human and animal waste (e.g., Diédhiou et al. 2012). Moreover, the same result can be observed between SO42– and Ca2 (r = 0.79). The high correlation implies that the dissolution of gypsum may be one of the key factors controlling the geochemical evolution of groundwater (Liu et al. 2015).

Table 2

Correlation between reference vectors for each parameter

NO3SO42–HCO3Na+K+Mg2+Ca2+
Cl 0.99* 0.82* −0.51* 0.47* 0.86* 0.46* 0.78*
NO3  0.75* −0.60* 0.38* 0.82* 0.36* 0.71*
SO42–   −0.03 0.84* 0.92* 0.79* 0.94*
HCO3    0.43* −0.11 0.52* 0.11
Na+     0.71* 0.92* 0.82*
K+      0.72* 0.94*
Mg2+       0.88*
NO3SO42–HCO3Na+K+Mg2+Ca2+
Cl 0.99* 0.82* −0.51* 0.47* 0.86* 0.46* 0.78*
NO3  0.75* −0.60* 0.38* 0.82* 0.36* 0.71*
SO42–   −0.03 0.84* 0.92* 0.79* 0.94*
HCO3    0.43* −0.11 0.52* 0.11
Na+     0.71* 0.92* 0.82*
K+      0.72* 0.94*
Mg2+       0.88*

*Correlations significant at p = 0.01.

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