[Characteristics of Organic Matter in Sediments During the Thermal Stratification of a Reservoir and Effects on an Aerobic Denitrifier].

In this study, the relative molecular weight distribution and fluorescent characteristics of the organic matter in sediments during the thermal stratification of a drinking water reservoir were studied. The nitrogen removal, growth performance, and carbon removal ability of an aerobic denitrifier were investigated when the organic matter in sediments was used as a carbon source. The results found that:① during the stratification period in the drinking water reservoir, the organic matter in sediments has a larger proportion of relative molecular mass>100×103. It can be observed that compared with the relative molecular weight distribution in different months, the percentage of macromolecular organic matter in sediments is the lowest in July (44.62%), showing a characteristic of smaller relative molecular weight; ② the organic matter in sediments of the drinking water reservoir was composed of terrestrial humic-like substance component C1 (250 nm, 425 nm), tryptophan and amino acid-like substances component C2 (230 nm/280 nm, 322 nm), and traditional microbial humic-like substances component C3 (250 nm, 340 nm). Component C2 accounted for a higher percentage, and the organic matter in July showed a higher total fluorescence intensity; ③ during the aerobic denitrification process, organic matter in May displayed better characteristics as an electron donor, while organic matter in July exhibited excellent performance as an energy substance and better denitrification characteristics of the strain WGX-9; ④ the aerobic denitrification performance of the strain WGX-9 can be significantly promoted when the organic matter in sediments is a carbon source, compared with natural organic matter, algae organic matter, and actual water of the drinking water reservoir. This study clarifies the characteristics of the organic matter in sediments during the thermal stratification period of the drinking water reservoir and its effect on an aerobic denitrifier. This will provide a scientific basis for the research of nitrogen pollution control in micro-polluted water sources.

[Effect of Artificial Mixing on Temporal and Spatial Succession of Algae Community Structure in Jinpen Reservoir].

To explore the effect mechanism of the artificial mixing process on the temporal and spatial succession of algae community structure in a water body, this study used water-lifting aerators to induce in-situ artificial mixing of the water body of Jinpen Reservoir, and in-situ spot physical-chemical parameters and algae of the water body of the reservoir were observed during an artificial mixing process. A total of 51 species of 28 genera of 6 families of algae were identified in the water body of the Jinpen Reservoir. The artificial mixing effect of the water-lifting aerators significantly inhibited the growth of algae in the water, and had a significant impact on the community structure. Before activation of the water-lifting aerators, algae were mainly distributed in the surface water body, and Chlorella vulgaris was the dominant species. With the operation of the water-lifting aerators, the algal density of surface water body decreased significantly, and the vertical distribution of the algae density in the water body tended to be uniform. The dominant species tended to succeed in Cyclotella sp. This study used the method of redundancy analysis, combined with critical depth theory and the characteristics of algae growth, to analyze the relationship between the spatial-temporal succession of algae community structure and the changes in the main physical-chemical parameters in Jinpen Reservoir during the artificial process. The analysis results showed that the artificial mixing of the water-lifting aerators mainly affects the temporal and spatial succession of the algae community structure by rapidly destroying the thermal stratification stability of the water body and significantly increasing the water mixing depth.

[Spatial and Temporal Succession Characteristics of Aerobic Anoxygenic Photosynthesis Bacteria in a Stratified Reservoir].

Aerobic anoxygenic photosynthesis bacteria (AAPB) play a significant role in the material circulation of the hydrosphere, with diverse community structure and unique metabolic functions. To investigate the spatial and temporal succession characteristics of AAPB abundance and community structure in Jinpen Reservoir, a quantitative real-time polymerase chain reaction and Illumina MiSeq high-throughput sequencing technique targeting the pufM gene were applied. Furthermore, redundancy analysis was used to determine the influence of environmental factors on their community structure. The results showed that the AAPB abundance ranged from (6.70±0.43)×103 to (2.69±0.15)×104 copies·mL-1, with the maximum value appearing in October, and decreased with an increase in water depth. Samples were mainly classified into 19 genera (except for the unclassified genus); the most abundant AAPB genera were Bradyrhizobium sp. and Methylobacterium sp., which were affiliated to the α-Proteobacteria, and the proportion of the Bradyrhizobium sp. was highest in November, accounting for more than 60% (except 10 m). Furthermore, Rubrivivax sp., belonging to ß-Proteobacteria, was found to have a low proportion. There was a strong interaction relationship between AAPB genera. For example, Rhodobacter sp. was positively correlated with Rhodovulum sp., while Hydrogenophaga sp. was negatively correlated with Bradyrhizobium sp.. The community structure composition and distribution of AAPB were significantly different, mainly affected by temperature (T), total nitrogen (TN), NO3--N, and light intensity and comprehensively regulated by environmental factors. For instance, T, TN, and total phosphorus had a significant impact on the AAPB community structure of water samples at 0, 5, and 15 m in October, whereas light intensity, pH, DO, and chlorophyll-a were major structuring factors in the AAPB assemblages of water samples at 5 m in December. The results have guiding significance for parsing the spatial and temporal variability of AAPB abundance and diversity in stratified reservoirs, and simultaneously provide a theoretical basis for exploring the driving factors of AAPB population structure.

[Release Mechanisms of Iron and Manganese from Sediments in Jinpen Reservoir].

In response to the annual hypolimnetic anoxia in stratified reservoirs, water-lifting aerators (WLAs) were used in Jinpen Reservoir to supplement the dissolved oxygen in the bottom water and suppress the release of reduced pollutants from sediment. However, due to the influence of geomorphic characteristics at the bottom of the reservoir, there were some differences in the efficiency of artificial mixing and aeration. After the deactivation of WLAs, the dissolved oxygen in the bottom water of some deeper areas was rapidly depleted, resulting in the re-release of pollutants. To explore the release mechanisms and diffusion intensity of iron and manganese during this period, the representative samples in the main reservoir area were collected to measure the distribution of dissolved iron and manganese in the pore water and overlying water and calculate the diffusive flux of dissolved iron and manganese across the sediment-water interface. The results showed that the bottom water of the lower terrain rapidly entered the anaerobic condition after the system was deactivated, resulting in the release of a large amount of dissolved manganese into the overlying water, the maximum concentration of which was 0.42 mg·L-1. However, the bottom water of the higher terrain briefly entered a state of hypoxia, after which the dissolved oxygen concentration increased rapidly, so the dissolved manganese concentration increased moderately to 0.17 mg·L-1. The distribution of iron and manganese in the pore-water-overlying water showed that the dissolved manganese was released more easily into the overlying water than the iron under anaerobic conditions and constant accumulation in the upper sediments and overlying water. However, the release of dissolved iron was not only suppressed by dissolved oxygen but also by other oxidants such as manganese oxide. The diffusion flux of dissolved manganese declined after the system was deactivated. A mass balance calculation demonstrated that the accumulation of dissolved manganese in the anaerobic layer was not only related to the diffusion flux but also to the sedimentation flux and the thickness of the anaerobic layer. Therefore, the biogeochemical cycle of iron and manganese in the anaerobic layer requires further study.