Mutant prevention concentrations of levofloxacin, pazufloxacin and ciprofloxacin for A. baumannii and mutations in gyrA and parC genes.

Fluoroquinolones are antimicrobial agents that are widely used clinically, but the increasing resistance of Acinetobacter baumannii (A. baumannii) to these agents is a matter of concern. We investigated mutant prevention concentrations (MPCs) of three fluoroquinolones, levofloxacin (LVX), pazufloxacin (PAZ) and ciprofloxacin (CIP). We analyzed an A. baumannii standard strain (ATCC19606) for mutation prevention indices (MPIs), MPCs and mutant selection windows as well as MICs of CIP, PAZ and LVX and compared the derived values with 34 A. baumannii strains collected in hospitals. In addition, A. baumannii standard strain (ATCC19606) fluoroquinolone-resistant mutants were investigated for gyrA and parC gene mutations. MPCs of CIP, prevention antibiotics concentration and LVX for A. baumannii ATCC19606 were 12.8, 5.6 and 2.8 µg ml(-1) and their MPIs were 16, 8 and 4, respectively. Clinically isolated A. baumannii strains had CIP, PAZ and LVX MPC value ranges of 1-8, 1-16 and 0.5-2 µg ml(-1) and their MPIs were 8, 8 and 4 µg ml(-1). Single gyrA mutations (Ser(83)-Leu(83)) occurred in 18 resistant strains (48.7%) and single parC mutations (Ala(79)-Asp(79) or (Ser(80)-Leu(80)) occurred in 8 resistant strains (21.6%), whereas gyrA and parC double mutations occurred in 2 (5.4%) of the resistant strains. MPC and MPI values of LVX were lower than that of CIP and PAZ. Single gyrA and parC mutations accounted for the majority of mutations (n=24), whereas double mutations occurred only in two strains.

Uncertainty analysis of total phosphorus spatial-temporal variations in the Yangtze River Estuary using different interpolation methods.

Interpolation processes and results are generally accompanied by uncertainty which affects the spatial and temporal properties of pollutants. Based on the 4 period sample data of total phosphorus (TP) collected from the Yangtze River Estuary (YRE) in 2010 and 2011, the uncertainty of spatial-temporal variation was analyzed with interpolation methods of inverse distance weighted (IDW), local polynomial interpolation (LPI), ordinary kriging (OK) and disjunctive kriging (DK). The root mean square errors (RMSE) and the mean relative errors (MRE) were used to analyze the accuracy of different interpolation methods. The results showed that the uncertainty of DK was the lowest and the uncertainty of LPI was the highest among the 4 methods. The subtraction results between different interpolation methods showed that there was some distinct area of value in the disparate interval (not in [-0.05, 0.05] (mg/L)) in the 4 seasonal results, which was mainly distributed in the boundary region and around some sample sites. Both standard deviation (SD) and coefficient of variance (CV) in August 2010 were the highest in the 4 seasons and annual mean. The uncertainty may be caused by choice of interpolation methods, spatial data discrepancy and the lack of sample data.

The stakeholder preference for best management practices in the Three Gorges Reservoir Region.

A qualitative analysis of in-depth interviews with 92 farmers and 42 policy managers in Wuxi County, the Three Gorges Reservoir Region, was conducted to identify stakeholder preferences for alternative best management practices (BMPs) and to determine the factors that affect their acceptance. Policy manager support for most of the practices was relatively stronger than support by farmers, except for the grade stabilization structure (GSS), hillside ditch (HD) and constructed wetland alternative, owing to their perceptions of soil benefits, economic advantages and environmental advantages. Farmers opposed those practices that occupied cultivated lands or changed the conventional planting methods, such as field border, conservation tillage (CT) and contour buffer strips. They tended to accept the BMPs with off-farm pollution reduction, such as GSS, riparian forest buffer and HD, and the BMPs associated with soil benefits, such as nutrient management and Terrace. The result that almost all respondents did not accept CT differed from reports in the existing literature. There is a significant correlation between the acceptance of some BMPs and the townships where the farmers lived (P ≤ 0.05). The environmental conditions and social factors would affect farmer support for BMPs, including local soil conditions, farming methods, economic income, education level and age. The economic advantages of the BMPs were the main motivation for farmers to accept the practices. Furthermore, intensive education efforts, financial incentives or economic subsidies may promote the adoption of the BMPs in our study area.

Runoff characteristics and nutrient loss mechanism from plain farmland under simulated rainfall conditions.

In recent years, nonpoint source (NPS) pollution has become the main contributor to water quality problems. Research on nitrogen (N) and phosphorus (P) losses from farmland and the factors that influence these losses is very meaningful both for increasing the crop yield and for improving environmental water quality. To explore the mechanism by which N and P are lost from farmland in the North China Plain (NCP), 16 simulated rainfalls were conducted in 14 experimental fields (each of which had different conditions) in the NCP from July to August in 2010. The results showed that the rainfall intensity, the antecedent soil moisture content, and the vegetation cover status were the main factors that affected the surface runoff in the NCP. The runoff volume increased with the increasing rainfall intensity and the increasing soil moisture content, and decreased with the increasing vegetation cover. These factors also significantly affected the losses of P and N. The losses of P and N were positively correlated with the rainfall intensity and the antecedent soil moisture content, and negatively correlated with the vegetation cover. A longer and more intense rainfall resulted in a higher loss of N and P. Dissolved nitrogen was the predominant form of N loss. For phosphorous, the predominant loss form was greatly influenced by the rainfall intensity, the vegetation cover, and the antecedent soil moisture content. Most of phosphorus existed as dissolved phosphorus in Baizhuang (BZ) and as particulate phosphorus in Tangcheng (TC) and Fentai (FT). The minimum requirements for runoff occurrence in experimental regions were a rainfall depth of 5.1mm, a rainfall intensity of 50mm/h, and an antecedent soil moisture of approximately 29.6%.

Historical trend of nitrogen and phosphorus loads from the upper Yangtze River basin and their responses to the Three Gorges Dam.

Excessive inputs of nitrogen and phosphorus (N and P) degrade surface water quality worldwide. Impoundment of reservoirs alters the N and P balance of a basin. In this study, riverine nutrient loads from the upper Yangtze River basin (YRB) at the Yichang station were estimated using Load Estimator (LOADEST). Long-term load trends and monthly variabilities during three sub-periods based on the construction phases of the Three Gorges Dam (TGD) were analyzed statistically. The dissolved inorganic nitrogen (DIN) loads from the upper YRB for the period from 1990 to 2009 ranged from 30.47 × 10(4) to 78.14 × 10(4) t, while the total phosphorus (TP) loads ranged from 2.54 × 10(4) to 7.85 × 10(4) t. DIN increased rapidly from 1995 to 2002 mainly as a result of increased fertilizer use. Statistics of fertilizer use in the upper YRB agreed on this point. However, the trend of the TP loads reflected the combined effect of removal by sedimentation in reservoirs and increased anthropogenic inputs. After the TGD impoundment in 2003, decreasing trends in both DIN and TP loads were found. The reduction in DIN was mainly caused by ammonium consumption and transference. From an analysis of monthly loads, it was found that DIN had a high correlation to discharges. For TP loads, an average decrease of 4.91 % in October was found when the TGD impoundment occurred, but an increase of 4.23 % also occurred in July, corresponding to the washout from sediment deposited in the reservoir before July. Results of this study revealed the TGD had affected nutrient loads in the basin, and it had played a role in nutrient reduction after its operation.

Spatial and temporal variations in nitrogen and phosphorous nutrients in the Yangtze River Estuary.

Based on spatial interpolation data from 2003 to 2010, combined with almost 30 years of nitrogen and phosphorus pollutant data, this research analyzed the variations in total nitrogen (TN), nitrate nitrogen (NO(3)-N), total phosphorus (TP) and phosphate-P (PO(4)-P) in the Yangtze River Estuary (YRE). On the annual and seasonal timescales, nitrogen and phosphorus concentrations exhibited increasing trends overall, and the fluctuations in the concentrations of TN, TP and PO(4)-P significantly increased during the last three decades, especially after 2003, because of the more prevalent human activities and nonpoint sources in the area. Specifically, a high-concentration area of TN was found downstream of the North Branch of the YRE. Considering the spatial distribution of the nutrients, combined with a tidal flood current and a time span of 7 years, the TN maximum increased from approximately 3.07mg/L to 4.48mg/L. The TP maximum also rose from approximately 0.25mg/L to 0.34mg/L because of a high-concentration area of TP in the South Branch of the YRE due to the confluence with the Huangpu River. Additionally, there was an expansion of high-concentration areas of TN (≥3.0mg/L) and of TP (≥0.20mg/L).