Effects of Seasonal Thermal Stratification on the Functional Diversity and Composition of the Microbial Community in a Drinking Water Reservoir

Xiao Yang,Haihan Zhang,Tinglin Huang

doi:10.3390/w7105525

Abstract

The microbial communities within reservoir ecosystems are shaped by water quality and hydrological characteristics. However, there are few studies focused on the effects of thermal stratification on the bacterial community diversity in drinking water reservoirs. In this study, we collected water samples from the Jinpen Reservoir around the re-stratification period. To explore the functional diversity and bacterial community composition, we used the Biolog method and 16S rRNA-based 454 pyrosequencing combined with flow cytometry. The results indicated that stratification of the reservoir had great effects on temperature and oxygen profiles, and both the functional diversity and the composition of the bacterial community strongly reflected the significant vertical stratification in the reservoir. The results of the Biolog method showed a significantly higher utilization of carbon sources in the hypolimnion than in the epilimnion. The result of pyrosequencing also showed a significantly higher species diversity and richness in the hypolimnion than in the epilimnion with different dominant phylum. Redundancy analysis also indicated that the majority of environmental variables, especially pH and dissolved oxygen, played key roles in shaping bacterial community composition. Our study provides a better understanding of the functional diversity of bacterial communities, and the response of microorganisms to seasonal thermal stratification.

Highlights

Reservoirs are the main source of urban drinking water in China, especially in arid and semiarid regions
Our redundancy analysis (RDA) results of pyrosequencing provided further evidence of the habitat heterogeneity theory, as microorganisms would shift in response and adaptation to the variation in aquatic environment, the bacterial community composition (BCC) of the Jinpen Reservoir was significantly correlated with the physicochemical variables of the environment, including pH, dissolved oxygen (DO), temperature, turbidity, specific conductivity (SpCond), NH4-N, total nitrogen (TN) and condition. Permanganate index (CODMn), especially the pH value and the oxygen concentration
The results of pyrosequencing showed that the hypolimnion had significantly higher values in diversity and abundance, and the cluster analysis results clearly showed that the bacterial community composition was strongly correlated with water stratification

Summary

Introduction

Reservoirs are the main source of urban drinking water in China, especially in arid and semiarid regions. Thermal regime is strongly associated with the hydrodynamics of these reservoirs, and the water column becomes seasonally thermally stratified and divided into the epilimnion, metalimnion, and hypolimnion [1,2,3]. The metalimnion would limit the transfer of oxygen from the surface to the deeper waters during the stratified period [4,5]. An extended period of anoxic condition in the hypolimnion may intensify the deterioration of the water quality [6,7]. The freshwater ecosystem of drinking water reservoirs usually contains a number of microorganisms which are strongly affected by the physical and chemical variables [8].

Methods

Results

Discussion

Conclusion