Characteristics of planktonic and sediment bacterial communities in a heavily polluted urban river.

Urban rivers represent a unique ecosystem in which pollution occurs regularly, altering the biogeochemical characteristics of waterbodies and sediments. However, little is presently known about the spatiotemporal patterns of planktonic and sediment bacterial community diversities and compositions in urban rivers. Herein, Illumina MiSeq high-throughput sequencing was performed to reveal the spatiotemporal dynamics of bacterial populations in Liangtan River, a heavily polluted urban river in Chongqing City (China). The results showed the richness and diversity of sediment bacteria were significantly higher than those of planktonic bacteria, whereas a strong overlap (46.7%) in OTUs was identified between water and sediment samples. Bacterial community composition remarkably differed in waters and sediments. Planktonic bacterial communities were dominated by Proteobacteria, Bacteroidetes, Cyanobacteria and Actinobacteria, while sediment bacterial communities mainly included Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Additionally, several taxonomic groups of potential bacterial pathogens showed an increasing trend in water and sediment samples from residential and industrial areas (RI). Variation partition analysis (VPA) indicated that temperature and nutrient were identified as the main drivers determining the planktonic and sediment bacterial assemblages. These results highlight that bacterial communities in the polluted urban river exhibit spatiotemporal variation due to the combined influence of environmental factors associated with sewage discharge and hydropower dams.

[Effects of Gypsum on CH4 Emission and Functional Microbial Communities in Paddy Soil].

In this study, the effects of gypsum (FGD) on CH4 emission and functional microbial community in paddy soil were identified under five treatments, including FGDG0(0 t·hm-2), FGDG1(2 t·hm-2), FGDG2(4 t·hm-2), FGDG3(8 t·hm-2), and FGDG4(16 t·hm-2). The methane flux was determined using static chamber and chromatography. Bacterial community structure and its effect on soil bacterial community structure, and the abundance of methanogenic and methanotrophs were measured via high-throughput sequencing and quantitative PCR. The results showed that after treatment with desulfurated gypsum, pH of the soil increased significantly (P<0.05). Redox potential, organic carbon, and available potassium content increased, with no significant difference (P>0.05). The average emission flux of CH4 reduced with the increase of desulfurated gypsum content, following the following trend:FGDG1 > FGDG2 > FGDG3 > FGDG4. They decreased by 31.56%, 57.30%, 83.60%, and 90.66%, respectively, compared with the control. Compared with the control, FGDG1 and FGDG2 increased the richness and variety of soil bacteria. However, when the application amount exceeds 4 t·hm-2, the richness and variety of soil bacteria decrease. Compared with the control, the relative abundance of sulfate-reducing bacteria in paddy soil increased significantly by 6.98%-13.56%. The abundance of the methane-oxidizing bacteria pmoA gene increased by 0.3%-6.2%. The abundance of the methanogen gene, mrcA decreased significantly by 2.4%-15.8%, while the abundance ratio (pmoA/mcrA)increased with the increase of the amount of desulfurated gypsum. Correlation analysis showed that the average emission of CH4 was markedly negatively correlated with the relative abundance of the sulfate-reducing bacteria and pmoA/mcrA percentage in soil, and significantly positively correlated with methanogenic gene, mcrA. In summary, desulfurated gypsum can improve the diversity of bacterial communities and reduce the emission of CH4 in the paddy soils.

[Effects of Bamboo Biochar on Greenhouse Gas Emissions During the Municipal Sludge Composting Process].

Effect of adding bamboo biochar into the compost at different dosages on greenhouse gas emissions was investigated by analyzing the dynamic characteristics of the process of municipal sludge composting with four different composts (S1:adding 2.5% bamboo biochar, S2:adding 5% bamboo biochar, S3:adding 10% bamboo biochar, CK:without bamboo biochar). The results showed that CH4 emissions mainly occurred during the heating period and the beginning of the altithermal period, accounting for 99.01%-99.81% of the total emissions. When the added bamboo biochar is less than 5%, CH4 emissions decrease with the increase in the amount of bamboo biochar. If it is more than 5%, CH4 emissions will clearly increase. CO2 emissions mainly occurred during the heating period and the altithermal period, accounting for 75.65%-86.58% of the total emissions. Adding bamboo biochar can reduce 3.37%-13.48% of the CO2 emissions but there is no significant difference between the treatments (P>0.05). N2O emissions mainly occurred during the heating period and the rotten period. Adding bamboo biochar can reduce the emissions of N2O; the more the amount of bamboo biochar, the less N2O emissions (P<0.05). The emission factors of CK, S1, S2, and S3 were 44.10, 37.57, 35.10, and 35.44 kg·t-1 of dry sludge, respectively. S1, S2, and S3 showed 14.81%-20.41% reduction in greenhouse gas emissions owing to the addition of bamboo biochar, indicating that bamboo biochar can reduce the carbon emissions in the process of sludge composting.