Simulation of suspended sediment transport in a floating canopy channel based on random displacement model.

In conventional research, the suspended sediment distribution in a channel under the action of floating canopy has been rarely studied. In this study, experiments on sediment transport in flume with fixed suspended vegetation were carried out under different velocity conditions. It was performed to examine the suspended sediment transport and distribution law as impacted by the floating canopy. The vertical distribution formula of velocity impacted by the floating canopy was derived based on improved two-layer theory. Combined with the random displacement model (RDM), a Lagrangian method was developed to simulate the suspended sediment transport under the action of the floating canopy. Compared with the experimental data, the R2 of vertical velocity simulation was higher than 0.96, and the vertical distribution of suspended sediment concentration varied significantly (4.64 to 19.83 g/L) following the vertical coordinate. Subsequently, the numerical model of sandy flow with the floating canopy was established by complying with the stratified sediment turbulence diffusion coefficient to predict the suspended sediment transport. Besides, the established numerical model can lay a theory basis for sediment transport in such channels (floating canopy channels).

Distribution, Phylogeny and Evolution of Clinical and Environmental Vibrio vulnificus Antibiotic-Resistant Genes.

Vibrio vulnificus is an emergent marine pathogen and is the cause of a deadly septicemia. However, the evolution mechanism of antibiotic-resistant genes (ARGs) is still unclear. Twenty-two high-quality complete genomes of V. vulnificus were obtained and grouped into 16 clinical isolates and 6 environmental isolates. Genomic annotations found 23 ARG orthologous genes, among which 14 ARGs were shared by V. vulnificus and other Vibrio members. Furthermore, those ARGs were located in their chromosomes, rather than in the plasmids. Phylogenomic reconstruction based on single-copy orthologous protein sequences and ARG protein sequences revealed that clinical and environmental V. vulnificus isolates were in a scattered distribution. The calculation of non-synonymous and synonymous substitutions indicated that most of ARGs evolved under purifying selection with the Ka/Ks ratios lower than one, while h-ns, rsmA, and soxR in several clinical isolates evolved under the positive selection with Ka/Ks ratios >1. Our result indicated that V. vulnificus antibiotic-resistant armory was not only confined to clinical isolates, but to environmental ones as well and clinical isolates inclined to accumulate beneficial non-synonymous substitutions that could be retained to improve competitiveness.

The bacterial community structure in epiphytic biofilm on submerged macrophyte Potamogetom crispus L. and its contribution to heavy metal accumulation in an urban industrial area in Hangzhou.

Submerged macrophytes and their epiphytic biofilms are important media for metal transport/transformation in aquatic environment. However, the bacterial community structure and the contribution of the epiphytic biofilm to the heavy metal accumulation remain unclear. Therefore, in this study, water, sediment, submerged macrophyte (Potamogeton crispus L.) and its epiphytic biofilm samples in three sites of the moat in the industrial area of Hangzhou were collected for analyzing. The bacterial community structure was significantly impacted by the TN concentrations, and Genus Aeromonas (24.5-41.8%), Acinetobacter (16.2-29.8%) and Pseudomonas (12.6-23.6%) dominated in all epiphytic biofilm samples, which had the heavy metal pollutant resistibility. The contents of Cr in biofilms (7.4-8.3 mg/kg, DW) were significantly higher than those in leaves (1.0-2.4 mg/kg, DW), while the contents of Cu (11.0-13.9 mg/kg, DW) in leaves were significantly higher than those in biofilms (0.7-3.9 mg/kg, DW) in all the three sites. The BCF values of metals in the biofilm were followed the order of YF < IC < ETS. The results indicated that the epiphytic biofilm had positive effects on the metal bioaccumulation, and the metal accumulation ability increased with the hydrodynamic forces. Bioaccumulation by the epiphytic biofilm may be an effective way for metal (especially Cr) remediation.

Removal of nitrate from agricultural runoff in biochar electrode based biofilm reactor: Performance and enhancement mechanisms.

A biochar electrode based biofilm reactor was developed for advanced removal of nitrate from agricultural runoff. The corn-straw (Zea mays L.) biochar formed at 500 °C has an adsorption capacity of NO3--N up to 2.659 mg g-1. After 45-day start-up phase, the removal efficiency of nitrate reached 93.4% when impressed current was 20 mA, hydraulic retention time was 12 h and chemical oxygen demand/total nitrogen (C/N) ratio was 0.56 without additional carbon source. In comparison, neither electrochemical reduction alone nor microbial denitrification alone could obtain the ideal nitrate removal efficiency. The results implied that bio-electrochemical reduction was the main way of nitrate removal in the biofilm electrode reactor (BER). The denitrification efficiency of 88.9% could still be obtained when C/N = 0. It is because biochar can significantly promote the utilization efficiency of cathode electrons by microorganisms. Thus, biochar is a promising electrode material, which provides a new idea for the optimization of BER.

Nitrogen transformation in slightly polluted surface water by a novel biofilm reactor: Long-term performance and microbial population characteristics.

This study proposes a modular floating biofilm reactor (MFBR) for in situ nitrogen removal from slightly polluted water in rivers using enriched indigenous microorganisms. Its main structure is a 60 cm × 60 cm × 90 cm rectangular reactor filled with hackettens. After a 96-day startup, the removal efficiencies of ammonia-N and total N (TN) reached 80% and 25%, respectively, with a hydraulic retention time (HRT) of 10 h, whereas those in a control reactor (without biofilm) were only 4.9% and 0.2%, respectively. The influences of HRT and dissolved oxygen (DO) were also investigated. As a key factor, HRT significantly affected the removal efficiencies of ammonia-N and TN. When HRT was close to the actual value for a river studied (2.4 min), the removal efficiencies of ammonia-N and TN were only 8.7% and 3.1%, respectively. Aeration increased the concentration of DO in water, which enhanced nitrification but inhibited denitrification. When HRT was 2.4 min, aeration intensity was 20 L/min; the ammonia-N and TN removal rates were 9.5 g/(m2·d) and 11.3 g/(m2·d), respectively. The results of microbial community analysis indicated that the microorganisms forming the biofilm were indigenous bacteria. The findings demonstrated a concept-proof of MFBR, which may be evaluated in scaling up investigation for developing a new methodology for nitrogen removal from slightly polluted surface water in plain river networks.

Characteristic monitoring of groundwater-salt transportation and input-output in inland arid irrigation area.

The rules of microscopic water-salt transportation can be revealed and the impact on the macroscopic water and soil resources can be further predicted by selecting a typical study area and carrying out continuous monitoring. In this paper, Jingtaichuan Electrical Lifting Irrigation District in Gansu Province (hereinafter called as JingDian irrigation district (JID)) located at the inland desert region of northwest China was selected as study area. Based on the groundwater-salt transportation data of representative groundwater monitoring wells in different hydrogeological units, the groundwater-salt evolution and transportation tendency in both closed and unclosed hydrogeological units were analyzed and the quantity relative ratio relationship of regional water-salt input-excretion was calculated. The results showed that the salt brought in by artificial irrigation accounts for the highest proportion of about 63.99% and the salt carried off by the discharge of irrigation water accounts for 66.42%, namely, the water-salt evolution and transportation were mainly controlled by artificial irrigation. As the general features of regional water-salt transportation, groundwater salinity and soil salt content variation were mainly decided by the transportation of soil soluble salt which showed an obvious symbiosis gathering regularity, but the differentiation with insoluble salt components was significant in the transportation process. Besides, groundwater salinity of the unclosed hydrogeological unit presented a periodically fluctuating trend, while the groundwater salinity and soil salt content in water and salt accumulation zone of the closed hydrogeological unit showed an increasing tendency, which formed the main occurrence area of soil secondary salinization.

Assessment model of ecoenvironmental vulnerability based on improved entropy weight method.

Assessment of ecoenvironmental vulnerability plays an important role in the guidance of regional planning, the construction and protection of ecological environment, which requires comprehensive consideration on regional resources, environment, ecology, society and other factors. Based on the driving mechanism and evolution characteristics of ecoenvironmental vulnerability in cold and arid regions of China, a novel evaluation index system on ecoenvironmental vulnerability is proposed in this paper. For the disadvantages of conventional entropy weight method, an improved entropy weight assessment model on ecoenvironmental vulnerability is developed and applied to evaluate the ecoenvironmental vulnerability in western Jilin Province of China. The assessing results indicate that the model is suitable for ecoenvironmental vulnerability assessment, and it shows more reasonable evaluation criterion, more distinct insights and satisfactory results combined with the practical conditions. The model can provide a new method for regional ecoenvironmental vulnerability evaluation.