[Evolution Characteristics and Driving Factors of Denitrification Community Based on Network Analysis in the Process of Spring Thermal Layer Formation in Zhoucun Reservoir].

Combined with on-site water quality investigation and nirS gene high-throughput sequencing technology, the evolution characteristics and influencing factors of the denitrification community during the formation of spring thermal stratification in Zhoucun Reservoir were analyzed. The results show that the water body stratification gradually formed during this period, and the environmental factors (NO3-, NH4+, TN, TOC, BOD5, permanganate index, TP, Fe, and Mn) showed significant differences (P<0.01); nitrogen showed a significant decline process. High-throughput sequencing provided 8703 OTU, which were divided into three phyla and eight major genera, proteobacteria accounted for the largest proportion with 45.27%-78.90%. The α-diversity except for the Simpson index showed that the ACE index, Chao index, Shannon index, and coverage index showed significant differences (P<0.05). The principal coordinate analysis showed the denitrification community exhibited significant differences in the spring, which was consistent with adonis result (P<0.001); network analysis (OTU-OTU) showed that there were seven main modules in this period, including 316 edges of 131 nodes, and the proportion of positive correlation edges was 95.25%. Network analysis (OTU-environmental factors) showed that there were five modules in this period, including 329 edges of 140 nodes, and the proportion of positive correlation edges was 51.98%. Sixty-two indicator OTU and 28 keystone OTU were obtained based on the indicator OTU analysis and network analysis. RDA and mantel test analysis indicated that T, DO, NO3-, TN, TOC, BOD5, and TP were the main environmental factors driving the denitrifying bacterial community structure and the key denitrifying OTU evolution in spring. Our results will provide technical support for the migration and transformation of nitrogen in reservoir water and pollution control.

[Analysis of Driving Factors on the Nitrogen Decrease in the Early Stage of the Thermal Stratification in Main Area of Zhoucun Reservoir].

In order to explore the trend and driving factors of nitrogen in the early stage of the thermal stratification in Zhoucun reservoir, the water quality indicators in main reservoir area of Zhoucun reservoir were monitored regularly form February to April (2016). Meanwhile, the fresh water and surface sediments in the sampling point were collected to study the effect of water and sediment denitrification by simulation in laboratory. The results showed that: the concentration of TN decreased from (2.28±0.09) mg·L-1 to (1.08±0.09) mg·L-1, the concentration of nitrate nitrogen decreased from (1.66±0.09) mg·L-1 to (0.25±0.06) mg·L-1, whereas the concentration of ammonia nitrogen and nitrite showed little change in the early thermal stratification of Zhoucun reservoir. At the same time, chlorophyll was not significantly increased, so the algae had little effect on nitrogen; the decreasing nitrogen was mainly due to the aerobic denitrification. Gradually increased temperature,the changes of DO and pH and the composition of organic matter (low molecular weight) were beneficial to the growth of aerobic denitrifying bacteria. Furthermore, the number of bacteria increased from 1.06×105 cfu·L-1 to 8.33×106 cfu·L-1, which enhanced the denitrification of the reservoir; Meanwhile, in the simulation experiments, the TN removal rates of water and water-sediment systems reached 0.7 mg and 3.3 mg, respectively. Water and sediment denitrification ratio was generally 1:4, and the aerobic denitrification of surface sediment was an important factor in the removal of nitrogen in reservoir.

[Analysis of Distribution Characteristics and Source of Dissolved Organic Matter from Zhoucun Reservoir in Summer Based on Fluorescence Spectroscopy and PARAFAC].

The fluorescent components were examined using excitation emission matrix fluorescence spectroscopy-parallel factor analysis technique for samples collected in August, 2015 from Zhouncun Reservoir. Principal component analysis was used to study the main factors and their relative contributions to DOM. Three fluorescent components were identified by PARAFAC, including fulvic-like component(C1:260,350/420 nm), protein-like(C2:280/360 nm) and humic-like (C3:270,390/530 nm) which showed the same source. The even spatial distribution of each component, higher total fluorescence intensity in storage port, high fluorescence index, high biological index, low humification index and the freshness index which was close to one showed that the DOM had a strong autochthonous contribution. The results of PCA showed that the autochthonous contribution reached 70.86%, and those three components of Zhoucun Reservoir could be connected with aph(440) by nonlinear multiple regression which means we can use the three-dimensional fluorescence spectrum results of DOM to control the pollution sources and indicate the eutrophication degree of Zhoucun Reservoir.

[Optical Characteristics of Dissolved Organic Matter from Two Different Full Mixed Reservoirs in Winter Based on UV-vis and EEMs].

The differences in the resource and characteristics of DOM between Zhoucun Reservoir and Jinpen Reservoir were studied by fluorescence ultraviolet-visible (UV-vis) and excitation-emission matrix spectra combined with parallel analysis (EEMs-PARAFAC). The results showed that three fluorescent components were identified by PARAFAC model in Zhoucun Reservoir and Jinpen Reservoir, including long wave humus-like component (C1: 350/460 nm), visible fulvic-like (C2: 335/410 nm) and protein-like (C3: 260,285/360 nm). However, the fluorescence intensity and the relative proportions of DOM exhibited significant difference (P<0.01) in two reservoirs. Moreover, the concentration of protein-like component in Zhoucun Reservoir was higher than that in Jinpen Reservoir, while the concentration of humus-like component presented the opposite trend. Based on the comparison of fluorescence index, biological index, humification index and the freshness index, the DOM of Zhoucun Reservoir where the land-use type was cultivated, livestock and residential, the internal pollution of sediments was serious, indicating a strong autochthonous component and aquatic bacterial origin, whereas the DOM of Jinpen Reservoir dominated by forest system had a higher terrigenous contribution in winter. From all the results, hydrological conditions of the reservoir and the characteristics of coastal ecological environment were important factors to influence the DOM sources and characteristics.

[Carbon Source Utilization Characteristics of Soil Microbial Community for Apple Orchard with Interplanting Herbage].

As soil fertility in apple orchard with clean tillage is declined continuously, interplanting herbage in orchard, which is a new orchard management model, plays an important role in improving orchard soil conditions. By using biolog micro-plate technique, this paper studied the functional diversity of soil microbial community under four species of management model in apple orchards, including clear tillage model, interplanting white clover model, interplanting small crown flower model and interplanting cocksfoot model, and the carbon source utilization characteristics of microbial community were explored, which could provide a reference for revealing driving mechanism of ecological process of orchard soil. The results showed that the functional diversity of microbial community had a significant difference among different treatments and in the order of white clover > small crown flower > cocksfoot > clear tillage. The correlation analysis showed that the average well color development (AWCD), Shannon index, Richness index and McIntosh index were all highly significantly positively correlated with soil organic carbon, total nitrogen, microbial biomass carbon, and Shannon index was significantly positively correlated with soil pH. The principal component analysis and the fingerprints of the physiological carbon metabolism of the microbial community demonstrated that grass treatments improved carbon source metabolic ability of soil microbial community, and the soil microbes with perennial legumes (White Clover and small crown flower) had a significantly higher utilization rate in carbohydrates (N-Acetyl-D-Glucosamine, D-Mannitol, ß-Methyl-D-Glucoside), amino acids (Glycyl-L-Glutamic acid, L-Serine, L-Threonine) and polymers (Tween 40, Glycogen) than the soil microbes with clear tillage. It was considered that different treatments had the unique microbial community structure and peculiar carbon source utilization characteristics.