Modeling Cadmium Transport in Neutral and Alkaline Soil Columns at Various Depths

Human health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water.Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6.The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils,and to investigate the parameters' variability with depth.The soil columns were 50 cm in length and 12.5 cm in diameter.Ceramic suction lysimeters were buried at depths of 2.5,7.5,17.5,27.5,and 37.5 cm to abstract soil solution.Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs).Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE.The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport.The hydrodynamic dispersion coefficient (D) ranged from 0.18 to 10.70 cm 2 h 1,showing large differences among different depths.The retardation factor (R d) ranged from 25.4 to 54.7 and the standard deviation of R d value was lower than 30% of the mean value.Precipitation coefficient (R p) decreased consistently with increasing depth,varying from 1.000 × 10 10 to 0.661 h 1.Sensitivity tests showed that D was less sensitive than R d.These results would be helpful in understanding the transport and retention of Cd in non-acidic soils.

Estimation of wind erosion from construction of a railway in arid Northwest China

A state-of-the-art wind erosion simulation model,the Wind Erosion Prediction System and the United States Environmental Protection Agency's AP 42 emission factors formula,were combined together to evaluate wind-blown dust emissions from various construction units from a railway construction project in the dry Gobi land in Northwest China.The influence of the climatic factors:temperature,precipitation,wind speed and direction,soil condition,protective measures,and construction disturbance were taken into account.Driven by daily and sub-daily climate data and using specific detailed management fles,the process-based WEPS model was able to express the beginning,active,and ending phases of construction,as well as the degree of disturbance for the entire scope of a construction project.The Lanzhou-Xinjiang High-speed Railway was selected as a representative study because of the diversities of different cli-mates,soil,and working schedule conditions that could be analyzed.Wind erosion from different working units included the building of roadbeds,bridges,plants,temporary houses,earth spoil and barrow pit areas,and vehicle transportation were calculated.The total wind erosion emissions,7406 t,for the first construction area of section LXS-15 with a 14.877 km length was obtained for quantitative analysis.The method used is applicable for evaluating wind erosion from other complex surface dis-turbance projects.