The freshwater volume accounts for about 3% of the total water volume globally, while the available freshwater to human beings is less than 3%, and there are still problems of uneven distribution and water pollution (Yang et al., 2017). The water quality and biosecurity of drinking water have been widely addressed (Gunnarsdottir et al., 2020). The water quality is closely affected by the structure and composition of the microbial community in the water (Wani et al., 2021). First of all, the composition of microbial communities will rapidly vary, once their habitats have changed slightly. Some studies have shown that there was a high concentration of chemical oxygen demand when the abundance of Bacillus and Firmicutes was high as well (Niu et al., 2019; Chen et al., 2020;). The results of Narsing et al. (2021) indicated that pH and temperature affected microbial diversity in Indian hot spring. Spriņġe et al. (2021) found that the counts in microbial indicators were affected by physicochemical parameters such as turbidity, temperature, and pH. In addition, microbial community reflect the structure and function of aquatic ecosystems (Jiang et al., 2021). Moreover, the microbial community is an important part of the biological community of the reservoir ecosystem and plays an important role in material cycle, energy flow, and information transfer. The detritus formed by the microbial community and their organic substrates is an important bait resource for fish in the reservoir (Zhao and Wei, 2018). The diversity, quantity, and special species of microbial community are often used as indicators for water quality. For example, the total coliforms, Thermotolerant coliforms, and Escherichia coli were used as key parameters in China Surface Water Environmental Quality Standard GB3838-2002 (Cui et al., 2015). It is well-known that some microbial community in the water are harmful to human health, such as pathogenic microbial community and some cyanobacteria which can release neurotoxins, hepatotoxin, cytotoxin, and endotoxin (Buratti et al., 2017). Therefore, it is crucial to investigate the microbial community composition and spatiotemporal distribution characteristics in drinking water reservoirs.
Previous studies showed that environmental factors, such as total nitrogen, pH and hydrodynamic force, etc., have great significance on the composition of the microbial community (e.g., Zeng et al., 2009; Read et al., 2015). In several polluted waters, the microbial community structure is also affected by contaminants (Song et al., 2021). Niu et al. (2019) found that the structure and compositions of the microbial community varied along the TGR (Three Gorges Reservoir), and the main environmental factors impacting the structure of the microbial community included PO43−, and COD (chemical oxygen demand). Previous work also found that the structural variation in microbial community was greater in summer than in winter (Jiang et al., 2021). In the Yangtze River, for instance, a previous study reported that mid-February to early March was a high risk period for algal blooms and the main contribution factors for algal blooms included water level, TP and water temperature (Cheng et al., 2019). The high salinity and nutrients were also found to induce dramatic declines in microbial species diversity (Tang et al., 2021). When the algae grew excessively, it often led to the production of toxins and decreasing of DO in the water. Thus, the survival of other aquatic organisms and water quality could be affected in most cases (Misra, 2011). Therefore, clarification of microbial community structure characteristics and their relationship with environmental factors has a great significance for the management of water quality, evaluation of water safety, and risks, which is extremely critical for the drinking water source reservoirs.
As the largest reservoir in Hainan Province, Songtao Reservoir has the largest source of fresh water in Hainan Province. It also has multiple functions such as irrigation, flood control, aquaculture, and navigation (Mo et al., 2016). Previous studies showed that pollutants are more likely to be deposited in reservoirs than in rivers, lakes, and other water bodies due to their slow water velocity and long retention time (Zamani et al., 2018). Thus, there was great concern over the water environment in Songtao Reservoir due to its ecological sensitivity and environmental significance. However, since the construction of Songtao Reservoir in 1963, there has been no research on the microbial community structure.
In this study, we studied the microbial community distribution characteristics and explored the influencing factors in Songtao Reservoir. Specifically, we used high throughput sequencing to detect the spatial and temporal diversity, and abundance of microbial community. We aimed to reveal the spatiotemporal variations of microbial communities in tropical reservoir. We further determined the key environmental factors influencing microbial community and aimed to provide critical information for the management of reservoir microbial community and drinking water safe.