X. B. Xu

Polybrominated diphenyl ethers in leaves and soil from typical electronic waste polluted area in South China

Polybrominated diphenyl ethers (PBDEs) in leaves and soil from typical e-waste polluted area in South China were investigated. The concentrations (ng/g dry weight) of PBDE congeners and ∑PBDE of five leaf samples were much lower than those in soil sample. The general patterns of ∑di-BDEs to ∑hepta-BDEs percentage distribution in leaf samples were similar to those of the soil sample, except the percentage of BDE209 which were lower than in soil. The percentages of ∑di-BDEs to ∑hepta-BDEs in soil were in the range of those in leaf samples. The results showed that the contamination of PBDEs in the leaf samples had good correlation with the soil around them.

Effects of Water-table Depth and Soil Moisture on Plant Biomass, Diversity, and Distribution at a Seasonally Flooded Wetland of Poyang Lake, China

Hydrological regime has been widely recognized as one of the major forces determining vegetation distribution in seasonally flooded wetland. Poyang Lake, the largest freshwater lake in China, has been encountering dramatic changes in hydrological conditions in last decade, which greatly influenced the wetland vegetations. To explore the relationships between hydrology and vegetation distribution, water-table depth, soil moisture, species composition, diversity and biomass were measured at a seasonally flooded wetland section at Wucheng National Nature Reserve. Three plant communities, Artemisia capillaris, Phragmites australis and Carex cinerascens communities, were examined which are zonally distributed from upland to lakeshore with decreasing elevation. Canonical correspondence analysis (CCA), spearmen correlation and logistic regression were adopted to analyze the relationships between vegetation characteristics and hydrological variables of water-table depth and soil moisture. Results show that significant hydrological gradient exist along the wetland transect. Water-table demonstrates a seasonal variation and is consistently deepest in A. capillaris community (ranging from–0.5 m above ground to +10.3 m below ground), intermediate in P. australis community (–2.6 m to +7.8 m) and shallowest in C. cinerascens community (–4.5 m to +6.1 m). Soil moisture is lowest and most variable in A. capillaris community, highest and least variable in P. australis community, and intermediate and moderate variable in C. cinerascens community. The CCA ordination indicated that variables of water-table depth and soil moisture are strongly related to community distribution, which explained 81.7% of the vegetation variations. Species diversity indices are significantly positively correlated with soil moisture and negatively correlated with moisture variability, while above- and belowground biomass are positively correlated with moisture. Above- and belowground biomass present Gaussian models along the gradient of average water-table depth in growing season, while species diversity indices show bimodal patterns. The optimal average water-table depths for above- and belowground biomass are 0.8 m and 0.5 m, respectively, and are 2.2 m and 2.4 m for species richness and Shannon-Wiener indices, respectively. Outcomes of this work improved the understandings of the relationship between hydrology and vegetation.

Contamination Status of Hexachlorobenzene (HCB) in Sandstorm Depositions from Beijing and the Origination Region

In China, sandstorms play an important role in the long-range atmospheric transport and deposition of hexachlorobenzene (HCB). Concentrations of HCB in sandstorm depositions sampled from Beijing and the origination region were measured to reveal HCB levels during atmospheric transport. The results suggested a constant level of HCB during atmospheric transport. The values were close to environmental background values indicating that no potential source of HCB existed along the transport route. A tendency for HCB levels in Beijing to increase from north to east was also observed, which was probably due to the influence of wind speed and industrial zone distribution.

Seepage Flow Field Measurement Technology in the Physical Simulation of a Low Permeability Reservoir

With the permeability of reservoirs becoming lower, the non-Darcy flow phenomenon becoming more obvious. The rules of fluid flow in low permeability reservoirs need to be researched through experimental method. The authors get the function relation between the ratio of resistivity and the concentration of solution through core experiments. The authors performed the single-phase fluid displacement experiment in low permeable natural sandstone plate model, then calculated the spreading condition of fluid in the model by recording the change of resistivity between measuring points. The application of resistivity method is verified the feasibility of measuring seepage flow field.

An Integrated Hydrological Model for Poyang Lake Watershed, China

An integrated model was established to simulate the Poyang lake watershed, which consists of a hydrological model for the catchment and a hydrodynamic model for the lake. The observed discharges at six main hydrological stations and the base flow index of groundwater were used as the objective functions for model calibration. The calibration results showed that the Nash-sutcliffe efficiency coefficients (Ens) for daily stream discharges varied from 0.71 to 0.84, and coefficients of determination (R2) varied from 0.70 to 0.88. The water levels of 4 stations in the lake were used to validate the Poyang lake hydrodynamic model. Results indicated that the fitting correlation coefficients of lake water levels at all stations were as high as 0.90. The proposed model as an integrated modeling approach can be used to simulate the effects of climate change and human activities in the catchment on the hydrology of Poyang lake.