| To investigate the evolutive characteristics of aquatic bacterial community under the seasonal thermal stratification in stratified resovirs, and to explore the response of aquatic bacterial community through destroying water stratification by water-lifting aeration technologies, we employed Biolog microplate, high-throughput sequencing, PCR-DGGE, flow cytometry and combined with environmental parameters. In this research, we had revealed how aquatic bacterial community drive the water paraments evolution and play roles in the biogeochemical cycles, and revealed the biological mechanism of the improvement of water quality by using water-lifting aerotors, from both the functional diversity and compostion diversity of the bacteria. The main contents were: the effects of stratification event on aquatic bacterial community in reservoirs; the evolutive characteristics of bacterial community under seasonal themal stratification; the diversity and the composition of sulfate-reducing bacteria in the sediment of Zhoucun Reservoir; the regulating effect on bacterial community and the enhanced effect on metabolic activity by wter-lifting aerator in reservoirs. The main conclusions are as following:(1) The succession of stratification in reservoirs casued the vertical gradient of physicochemical conditions and the habitat heterogeneity within the water column. The aquatic bacterial community showed significant stratified variations during the stratification in Shibianyu Reservoir, Jinpen Reservoir and Zhoucun Reservoir, and the diversity indices and the richness estimates in aerobic water layer were lower than that of anaerobic water layer. Additionally, the stratified variations of bacterial community had strongly reflected the vertical gradient of water temperature, dissolved oxygen, p H value and nutrition concentration in Zhoucun Reservoir.(2) The result had reveal the variation characteristics of bacterial metabolic activity in reservoirs. During the mixing period, the metabolic ability of main carbon sources kept balance with similar utilizations. However, after the water body became stratified, the balance had been destroyed, which leading to higher utilizations of esters, amines and carbohydrates than that of amino acids, alcohols and carboxylic acids. In addition, the average metabolic activity was lower in stratified period than in mixing period, while the total organic carbon showed increasing trend during stratification. The result indicated that the stratification could reduce the microorganism degradation to the organic pollutant in water.(3) The vertical structure of bacterial community maintain uniform during the mixing period, and Proteobacteria was one of the dominant phyla in reservoirs. However, during the stratified period, there was a strong vertical variation in the compostion of the bacterial community. Cyanobacteria became the most abundant phylum at the oxygenated surface, and the vertical distribution corresponded to the vertical gradient of p H value. Proteobacteria had bloomed in the anerobic water layer of Zhoucun reservoir due to the deterioration of water quality by endogenous pollution, and the maximum reached at 80.7% of the total bacteria.The biogeochemical cycles of Zhoucun Reservoir showed seasonal change characteristics with stratification. During the stratified period, the bacterial groups which played roles in nitrogen cycle and sulfur cycle had increased from mixing period; the methanotrophy/methylotrophy, such as Methylocaldum and Methylomonas, had bloomed in the anerobic water layer; the sulfate-reducing bacteria had increasd to 5.1% in the bottom water while the sulfide content increased to 1.281 mg/L, which indicated that they had the uniformity. Combined with the environmental parameters, the majority of environmental variables, especially p H and dissolved oxygen, played key roles in shaping bacterial community composition.(4) There was a relatively higher concentration of oganic matters and sulfide in the sediment in the main reservoir of the Zhoucun Reservoir with the highest value of acid-volatile sulfide at 205.9 μg/g, and the maximum of sulfate-reducing bacteria reached at 1.15×105 cells/g. The result of PCR-DGGE showed that the dominant sulfate-reduicng bacteria were Desulfobacterium and Desulfobulbus in the main reservoir, which played significant role in shaping the dominant species in the water column. The organic matter, the concentrations of nitrogen and phosphorus in the sediments were significantly correlated with the diversity of SRB communities present.(5) Under the mixing and aeration conditions of the water-lifting aerators, the stratified variations of the bacterial community was destroyed, and the vertical structure of bacterial community became uniform. The result showed that Cyanobacteria in the oxygenated surface and the anaerobic bacteria could be reduced efficiently under the effect of mixing and oxygenate by water-lifting aerators, and the proportion of Cyanobacteria became less than 5% after the operation from 47.4% in Jinpen Reservoir. Additionally, the operation did a strong inhibition effect on the bloom of Proteobacteria by improving the water quality. The proportion of sulfate-reducing bacteria had been reduced by 78.8% while the sulfide content had been cut by 98.3% after the operation. In addition, the water-lifting aerotors had a stong enhanced effect to in-situ denitrifiers: the proportion potential aerobic denitrifier in Jinpen Reservoir reached at 14.9% after the operation; the typical aerobic denitrifier groups, such as Pseudomonas, showed an extremely increasing trend under the effect; the dissolved total nitrogen had been cut by 86.1%.Under the water-lifting aeration, there was an obviously increasing of the functional diversity indices, which indicated the increasing of meatolic activity of aquatic bacterial community. On the basis of the the metabolic ability of main carbon sources restoring balance, the utilizations of carbohydrates and amines had significantly increased after the operation, and the growth of the metabolic activity on D-Xylose, α-D-Lactose and other sole carbon sources were more than 100%. The total organic carbon had been cut by 32%, which indicated that the organic pollutant had been degraded more effectively. Combined with environmental parameters, the dissolved oxygen, p H and total phosphorus, which were significantly changed by water-lifting aerators, played key roles in increasing the metabolic ability of the bacterial community.(6) For the aerobic denitrifiers which were isolated by our research group, this study had investigated the ecological and biological safety of the efficient strain to luminous bacteria and zebrafish. The result indicated that the increasing of aerobic denitrifiers could not destroy the balance of aquatic bacterial structure; the efficient strain could not represent a threat to the drinking water quality; the efficient strain had no toxicity or pathogenicity to aquatic animals. |
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