A new model to predict soil thermal conductivity.

Thermal conductivity is a basic parameter of soil heat transferring, playing an important role in many fields including groundwater withdrawal, ground source heat pump, and heat storage in soils. However, it usually requires a lot of time and efforts to obtain soil thermal conductivity. To conveniently obtain accurate soil thermal conductivity, a new model describes the relationship between soil thermal conductivity (λ) and degree of saturation (Sr) was proposed in this study. Dry soil thermal conductivity (λdry) and saturated soil thermal conductivity (λsat) were described using a linear expression and a geometric mean model, respectively. A quadratic function with one constant was added to calculate λ beyond the lower λdry and upper λsat limit conditions. The proposed model is compared with five other frequently used models and measured data for 51 soil samples ranging from sand to silty clay loam. Results show that the proposed model match the measured data well. The proposed model can be used to determine soil thermal conductivity of a variety of soil textures over a wide range of water content.

[Characteristics and Driving Mechanisms of Shallow Groundwater Chemistry in Xining City].

Groundwater is one of the major sources of water supply, especially in the western arid regions. However, with the deepening of the western development strategy, industrialization and urbanization have increased groundwater resource demands in Xining City. Overexploitation and utilization have led to a series of changes in the groundwater environment. Identifying the chemical evolution characteristics and formation mechanism of groundwater is crucial for preventing its deterioration and ensuring sustainable use. By combining hydrochemistry and multivariate statistical techniques, the chemical characteristics of groundwater in Xining City were analyzed, and the formation mechanism of groundwater and the influence of different factors were discussed. The results showed that there were as many as 36 chemical types of shallow groundwater in Xining City, mainly HCO3-Ca(Mg) (60.00%) and HCO3·SO4-Ca(Mg) (11.81%). There were 5-6 types of groundwater chemical types in bare land, grassland, and woodland. Groundwater chemical types in construction land and cultivated land were more complex, up to 21 types, indicating that they were strongly affected by human activities. The chemical evolution process of groundwater in the study area was mainly affected by rock weathering and leaching, evaporative crystallization, and cation exchange. The main controlling factors were water-rock interaction (contribution rate 27.56%) and industrial wastewater discharge (contribution rate 16.16%), acid-base environment (contribution rate 16.00%), excessive application of chemical fertilizers and pesticides (contribution rate 13.11%), and domestic sewage (contribution rate 8.82%). On account of the chemical characteristics of groundwater in Xining City and the influence of human activities, the management and control suggestions on the development and utilization of groundwater resources were put forward.