# Spatial Variations in Microbial Compositions in a
## 3 Results and Discussion
### Microbial Composition  
A total of 327,973 sequences and 26,221 OTUs were obtained from the tests conducted on the nine water samples in this study. Figure 8 shows that there are some variations in the compositions at the phylum level among the samples. A total of 14 phyla were identified in the nine samples. Figure 8 describes the distribution of the bacterial groups. The large bacterial proportions were identified as Proteobacteria, Bacteriodetes, Actinobacteria, Verrucomicrobia, Acidobacteria, Planctomycetes and Firmicutes. Smaller proportions of Parcubacteria, Peregrinibacteria, Saccharomyces, Cyanobacteria, Nitrospirae, Gemmatimonadetes and Chloroflexi were also identified. Proteobacteria was the most abundant phylum in all the samples, at 28.79-73.20%. Bacterodetes were the second most abundant phylum at 7.95-30.40%. Actinobacteria was the other prevalent phylum in water samples HMS14 (47.31%), HMS11 (45.60%), HMS8 (6.05%), HMS2 (5.37%), SJS1 (3.79%), YSS3 (3.35%) and HMS1 (1.94%). The phylum compositions of HMS11 and HMS14 showed a similarity, with high proportions of Actinobacteria and the absence of Acidobacteria. Both of these sample points were located close to the East Sea. Furthermore, samples KSG1 and SJS4 also did not have Acidobacteria. Figure 7: Gibbs plots of the karst stream water samples. Figure 8: Taxonomic classification of bacteria reads at phylum and class level, and UniFrac UCKMA clustering of the bacteria communities. KGS1 had a monotonous taxonomy, comprised of Proteobacteria and Bacteriodetes. KGS1 is located in a limestone mining area where mining activity is causing rapid environmental changes. Extreme environmental changes, such as mining in the karst environment, could trigger the reduction of species or the abundance of special species, which can be more pronounced than the effect of sea water [40]. In HMS2, bacteria belonging to the phyla Gemmatimonadetes and Chloroflexi comprise 1.08% and 1.78% of all the bacterial communities, respectively. The presence of Gemmatimonadetes suggests an adaptation to low soil moisture in the environmental sample [53]. Among the Proteobacteria, \(\beta\)-Proteobacteria was the most commonly present class, with abundances of 62.5%, 34.2%, 25.2%, 24.4%, 19.3%, 17.3%, 17.2%, 16.7% and 9.9%, in the samples HMS1, HMS2, HMS8, HMS11, HMS14, KGS1, SJS1, SJS4 and YSS3, respectively. UniFrac cluster analyses for each of the points showed that the bacterial communities in HMS11 and HMS14, though highly similar, were significantly different from those associated with KGS1. HMS11 and HMS14 are located adjacent to the East Sea. Actinobacteria are highly affected by the presence of sulfide and chloride [54]. The results suggest that the presence of specific bacteria, based on taxonomic classification at the sampling locations, may reflect the hydrological characteristics of the corresponding water samples, except for samples HMS11 and HMS14, in which 50% of the sequences were classified at the Actinobacteria phylum level. Moreover, Figure 9 shows the phylum compositions of samples based on the hydrogeological types of the samples, that is, from sinkhole and spring points. A clear distinction was evident in the microbial community based on hydrogeological conditions. Proteobacteria, Bacteroidetes and Verrucomicroba were the major phyla in both the spring and sinkhole point samples. However, the spring points were heavily loaded with Actinobacteria. In particular, Firmicutes were only present in the spring points at a level 4.3%. These microbial composition results are consistent with the hydrogeological composition results. Furthermore, variations in the ecological indices may indicate the substantial influence exerted by the surrounding environment on the spring and sinkhole waters during transport within the karst areas.