Xilai Zheng

Determination of Nutrient Fluxes Across the Sediment-Water Interface in a Nitrate-Rich Reservoir

This study was to quantify the interfacial flux of nutrients and to explore the potential effects of nitrate on phosphate release from sediments in a nitrate-rich reservoir. Typical sediment samples were collected from the Tianzhuang Reservoir. Porewater profiles of nutrients (Nitrate, ammonium, and soluble reactive phosphorus) and diffusive fluxes of these nutrients across the sediment-water interface were determined. The interfacial flux of NH₄ ⁺-N, NO₃ ^--N, and PO₄ ^3--P were 141.39~175.83 mg/(m²ldrd), -43.68~-42.50 mg/(m²ldrd), and 0.14 mg/(m²ldrd), respectively. The results show that the sediment is an important source for NH₄ ⁺-N, and a sink for NO₃ ^--N. The high nitrate rate into sediments indicates that denitrification is actively occurring in the anoxic surflcial sediments. In addition, the increase of phosphate concentration coincides with the decrease of nitrate concentration in the porewaters of sediments ranging from the interface down to about 7.5 cm. These evidence suggest that nitrate in overlying water may retard the phosphate release from the redox-sensitive sediments. This retard effect has to be considered when countering nitrogen pollution by decreasing external loadings of nitrate.

A Critical Salt Concentration of Illite Clay for Particle Release in Aquifer Media

Particle release is the main reason for permeability decrease in the coastal aquifers with the existence of illite clay. In this paper, an attempt was made to determine the CSC with both batch and column experiments. Stepwise decreasing concentrations of NaCl solution were applied until fine particles were released from the sediments and the CSC was determined. The critical oscillation frequency of batch experiment was determined at 150 rpm. The critical salt concentration was 0.054 mol/l determined by column experiments and 0.06 ±± 0.005 mol/l by batch experiments, respectively. CSC from batch experiments were compared to those obtained from column experiments. It was found that both of results were nearly consistent with each other. The flow velocity had little impact on the critical salt concentration in those experiments, while ion valence had a significant impact on the critical salt concentration.

Influencing Factors of BTEX Volatilization

Laboratory experiments were employed to investigate the influencing factors of BTEX volatilization. Characteristic of BTEX compounds was critical factor of volatilization; the higher saturated vapor pressure, the greater volatilizing speed. Type and structure of underlying materials determined the volatilization kinetics mode, the influence of channel blocking and adsorption of soils was stronger than that of enlarge volatizing area. The volatilizing speed remark-ably increased with increasing temperature. While the content and percentage of BTEX hardly made a difference to volatilization.

An experimental study of unsaturated vertical infiltration based on sand samples from ephemeral streams

Unsaturated vertical infiltration tests were conducted based on sand samples from ephemeral streams to determine the main factors that may affect vertical infiltration. According to test results, the infiltration rate changes with time in 3 stages. Stage 1 is marked by a sharp descent; Stage 2 features a slow descent; and Stage 3 is characterized by a gradually steadied infiltration rate. The initial water content and texture of the sand samples have obvious influences on the infiltration rate. The vertical infiltration rate decreases with the increase of initial water content or dry density of sand samples, and increases with the increase of grain size. Coarse sand has a steadier infiltration rate than fine sand. The experimental results were analyzed and evaluated using soil water movement and potential theories.

Water Quality Assessment and Spatial-Temporal Distribution of Nitrogen in the Tianzhuang Reservoir

The water quality of the Tianzhuang Reservoir and its inflows were assessed with the single factor index method to identify the main pollution factor of the reservoir. The spatial-temporal distribution of nitrogen were analyzed to gross judge the main pollution sources. The results indicate NO3--N accounts for more than 65% of the TN in the Tianzhuang Reservoir. The water quality cannot meet Ⅴ grade of the Environmental Quality Standards for surface Water for NH3-N and TN exceeding the respective standard. The NO3--N concentration of the reservoir equals to that of the inflows which affect by non-point source pollution (NPS) from agricultural areas. Therefore NPS is the main pollution source for NO3--N of the reservoir. In addition, the bottom sediments are the important pollution source for NH3-N. The results can aid in identifying the key pollutants and their sources of the reservoir.

Adsorption of Diesel Oil in Seawater by Biodegradable Adsorbing Material

The adsorption of diesel oil in seawater on biodegradable adsorbing material and the influencing factors such as salinity, pH and temperature were studied. Results showed the adsorption of diesel fitted the second-order reaction model, and the saturated adsorption capability was 6.69g/g which can be reached in 10-20min. The diesel oil removal efficiency increased with the increment of salinity and pH of seawater, and decreased when the environmental temperature rose. The adsorption isotherms could be described as Freundlichs and BET equation.

Changes of Hydraulic Conductivity in Coastal Aquifers with the Existence of Illites

Hydraulic conductivity of aquifers is one of important hydrogeological parameters in the seawater-freshwater field, which has a great influence on the scale and extent of seawater intrusion. Columns were subject to a pulse of seawater followed by fresh water or brackish water. Outflow rates and changes in hydraulic head as well as electric conductivity and particle concentrations were monitored over time. Permeability decrease occurred and no particles were found in the outflow when seawater was flushed by fresh water. However, when the concentration of the inflow solution for this replacement decreased gradually, particle releases occurred and permeability also decreased. Results indicate that there exists a distinct variation of permeability of aquifer media in the seawater-freshwater interface, namely a critical value existing in those experiments. The analysis of the experiments suggests deflocculation and release process of illite are the main factors of permeability reduction of sand columns.

Isolation and Biodegradation Characteristic of Petroleum Degrading Bacteria from Jiaozhou Bay

Twenty-eight bacterial strains capable of utilizing the petroleum were isolated from coastal areas along Jiaozhou Bay, Qingdao, China. The biodegradation of diesel and crude oil in seawater by mixed cultures of hydrocarbon-degrading bacteria was investigated. The mixtures or consortia of bacteria, denoted as Consortium 1 and Consortium 2 consisted of 5 bacterial strains, respectively. Consortium 1 was more efficient degrading diesel oil in seawater compared to consortium 2; Consortium 2 could effectively remove crude oil in seawater after a 30-day incubation period. The degradation process fits to a first order model, and consortium 1 had the highest capability in using diesel oil for its growth than consortium 2.

Effects of Dispersant Addition on Diesel Oil Biodegradation in Marine Environment

To evaluate the influence of the dispersant GM that was widely used in China on the biodegradation of diesel oil spilled in seawater, experiments were done under laboratory conditions at different salinities, temperatures with varied dispersant concentration .The results indicate that the concentration of dispersant added in seawater, seawater salinity and temperature are important factors affecting diesel oil biodegradation. The addition of dispersant in seawater is optimal when it was added in the ratio of 2:10(v/v), and the biodegradation rate reach the maximum value when the salinity is 33 g/l and the temperature is 30℃. However, because our tests were conducted in laboratory, considerable caution should be used in extrapolating these laboratory studies to field conditions.

Study on the Moisture Content of Loess Stratum in Xi'an Region

On the basis of field investigation, the change characteristic of moisture content of loess in Xi’an region has been studied by analysing the moisture content and particulate component. The result shows that the moisture content of the loess has the character of undulate change and increases from top to bottom in the same loess section. The apex is in the paleosol and the trough lies in the loess stratum. The moisture content from top to bottom in the loess stratum with the calcium carbonate nodule decreases firstly and then increases, and the peak situates above the calcium carbonate nodule because these nodules are of aquiclude effects. On the contrary the moisture content from top to bottom in paleosol stratum increases first then decreases, and the highest value lies in the middle or lower of the section , where the contents of clay particulate is the biggest. These findings demonstrate that the important factor affecting the moisture content is the soil character, and the content of moisture and clay particulate are significantly positive correlation. Keywordsloess stratum, moisture content, the calcium carbonate nodule, clay particulate