Abstract
Water eutrophication is a global ecological issue, and thermal stratification of water bodies can enable eutrophication. We examined bacterial communities in the stratified water columns and sediments in two different trophic reservoirs along the Wujiang River using quantitative real-time PCR and high-throughput sequencing. Bacterial 16S rRNA gene copies varied from 3.70 × 107to 5.27 × 108copies/L in the water column of Hongjiadu (HJD) Reservoir (60 m water depth) with slightly stratified variation; while in Wujiangdu (WJD) Reservoir (70 m water depth), bacterial abundance decreased markedly from the surface to the bottom(1.74 × 109to 2.38 × 107copies/L). The vertical distribution patterns of bacteria in both reservoirs resembled those of water Chlorophylla(Chla) concentrations. The abundance was negatively correlated with water depth (D), total nitrogen (TN), nitrate (NO3–-N), and positively correlated with water temperature (T) and dissolved oxygen (DO) level. In contrast, the alpha diversity of bacteria showed the opposite trend in the vertical water column.Proteobacteria,Actinobacteria, andBacteroideteswere the predominant phyla in the water column of both reservoirs. Compared to WJD Reservoir, HJD Reservoir displayed marked vertical spatial difference in bacterial community structure during thermal stratification. In particular,Pseudomonaswas frequently detected at the bottom of the HJD Reservoir. These results were consistent with predictive metagenomic profiling that revealed different vertical functional variation patterns of the bacterial communities in the two reservoirs. The bacterial community structure of HJD Reservoir was associated with water D, ammonium (NH4+-N), nitrite (NO2–-N), and total phosphorus (TP). The community structure of WJD Reservoir was related to water T, Chla, NO3–-N, and TN. The findings highlighted the important roles played by thermal stratification and nutrients in shaping the water bacterial community structure. Additionally, the absolute abundance of water nitrifiers (AOBgene copies) and denitrifiers (narG,nirS,norB, andnosZgene copies) displayed significant vertical differences in the water columns of both reservoirs. Gene copies involved in denitrification were significantly higher than those involved in nitrification. Water phosphorus and nitrogen contents were important variables influencing the absolute abundance of ammonia oxidizers and denitrifying bacteria, respectively. Our study revealed that the emergence of thermal stratification was responsible for the vertical stratification of bacteria in water and affected the bacterial community structure together with nutrients.
Highlights
Water eutrophication has become one of the major environmental issues affecting lakes and reservoirs on a global scale (Paerl et al, 2016; Wang et al, 2019)
Copy numbers of bacterial 16S rRNA genes slightly increased at 5 m and slightly decreased at 30 m in HJD Reservoir, while the decrease was greater in WJD Reservoir (Figure 2)
We examined the bacterial community structures based on quantitative real-time PCR and high-throughput sequencing in two different trophic reservoirs
Summary
Water eutrophication has become one of the major environmental issues affecting lakes and reservoirs on a global scale (Paerl et al, 2016; Wang et al, 2019). Artificial reservoirs generally exhibit hydrodynamic variations and longer exchange periods (Jardim et al, 2020). Numerous nutrients, such as nitrogen (N) and phosphorus (P) are intercepted, which alter the nutrient cycle, drive the rapid propagation of algae and other plankton, and decrease the dissolved oxygen (DO) content in the water body (Van Cappellen and Maavara, 2016; Shi et al, 2017; Petty et al, 2020), thereby worsening the eutrophication of the water body. Water stratification may be one of the major factors determining the vertical distribution of phytoplankton, which leads to the death of aquatic organisms, such as fish, in affected lakes. Little is known about the effect of water thermal stratification on the abundance of bacteria in reservoirs (Yu et al, 2014; Wang et al, 2015; Yang et al, 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
