# Spatial Variations in Microbial Compositions in a
## 3 Results and Discussion  
### Water Characteristics  
The hydrogeochemical parameters, such as temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), oxidation-reduction potential (ORP), turbidity, Ca\({}^{2+}\), Mg\({}^{2+}\), Na\({}^{+}\), K\({}^{+}\), HCO\({}_{3}\)\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), Cl\({}^{-}\) and NO\({}_{3}\)\({}^{-}\), were measured in the collected sink and spring waters from Hamaengbang (\(n=5\)), Kyogok (\(n=1\)), Yeosam (\(n=1\)) and Sajik (\(n=2\)) (Table 1). In this study, there are several potential sources or formation mechanisms for the Ca-Mg-HCO\({}_{3}\), Ca-Mg-SO\({}_{4}\) and Ca-Mg-Cl in the waters from the sinkhole and spring points. Characterization of the reflected hydrogeological characteristics of the karst area using Piper diagrams shows that the overall chemical character falls within the normal alkaline earth water group, indicating a predominantly Ca-Mg-HCO\({}_{3}\) water type (Figure 6). The chemical composition of the water is partly attributed to the dissolution of silicate minerals in the bedrock, and aluminosilicates in the weathered regolith. The occurrence of Ca-Mg-SO\({}_{4}\) in the study area is very unlikely to be attributed to the hydrogeological characteristics of the karst area, and it is probably effected by anthropogenic activities. Therefore, further studies are required to understand the possible evolution of this water type, especially in the case where the Ca-Mg-HCO\({}_{3}\) type of water in the groundwater of the recharge area changes to the Ca-Mg-SO\({}_{4}\) type along the direction of the water recharge points. The SJS sampling points, representing the recharge water within the residential areas of the study area, display higher major ion concentrations of SO\({}_{4}\) and Cl than were found in the spring waters. Besides this, the KGS point is located adjacent to the limestone mine. This increase in SO\({}_{4}\) and Cl is effected by anthropogenic activities, implying that the recharge area is directly affected by pollutants from the surface [6]. Therefore, attention should be paid to water quality management in the recharge area of the karst area. Figure 6: Piper diagram showing water types using major cations and anions in the sampled stream waters in the karst area (red circles indicate spring waters and blue marks indicate sinkhole waters). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c c c c c c c} \hline \multicolumn{12}{c}{**Familiar**} & \multicolumn{12}{c}{**Hain-Hanging Area**} & \multicolumn{12}{c}{**Kypical Area**} & \multicolumn{12}{c}{**Kypical Area**} & \multicolumn{12}{c}{**Kypical Area**} \\ \cline{2-12} \cline{12-12} \multicolumn{12}{c}{**Familiar**} & **m.** & **Max. ** & **Mean. ** & **S0. ** & **CV\({}^{m}\) & **a** & **Max. ** & **  
Major ion chemistry of the stream water is an important tool for determining solute sources, and for describing water evolution as a result of water-rock interaction that leads to the dissolution of carbonate minerals, silicate weathering and ion-exchange processes [6; 49; 50]. Hydrochemical data are plotted in the Gibbs diagram (Figure 7) to understand the source of the solutes. The [PERSON] (1970) diagram is a powerful and widely used tool for analyzing geochemical processes and trends in natural waters [51; 52]. It assumes that a clear semi-logarithmic diagram of TDS (ordinate) versus the weight ratio of Cl\({}^{-}\)/(Cl\({}^{-}\) + HCO\({}_{3}\)\({}^{-}\)), or Na\({}^{+}\)/(Na\({}^{+}\) + Ca\({}^{2+}\)), provides information on the relative importance of three major mechanisms controlling hydrochemistry: evaporation-crystallization, rock weathering and atmospheric precipitation. All the analyzed stream water samples fall in the rock weathering dominance area of the plot, which suggests that chemical weathering of the rock-forming minerals is the main process that contributes ions to the stream waters.