Vertical distribution characteristics of soil saturated hydraulic conductivity under different land use patterns in the Mu Us sandy land

Background,aim,and scope Soil saturated hydraulic conductivity(K_(s))is a key parameter in the hydrological cycle of soil;however,we have very limited understanding of K_(s) characteristics and the factors that inf luence this key parameter in the Mu Us sandy land(MUSL).Quantifying the impact of changes in land use in the Mu Us sandy land on K_(s) will provide a key foundation for understanding the regional water cycle,but will also provide a scientific basis for the governance of the MUSL.Materials and methods In this study,we determined K_(s) and the basic physical and chemical properties of soil(i.e.,organic matter,bulk density,and soil particle composition)within the first 100 cm layer of four different land use patterns(farmland,tree,shrub,and grassland)in the MUSL.The vertical variation of K_(s) and the factors that influence this key parameter were analyzed and a transfer function for estimating K_(s) was established based on a multiple stepwise regression model.Results The K_(s) of farmland,tree,and shrub increased gradually with soil depth while that of grassland remained unchanged.The K_(s) of the four patterns of land use were moderately variable;mean K_(s)values were ranked as follows:grassland(1.38 mm·min^(-1))<tree(1.76 mm·min^(-1))<farmland(1.82 mm·min^(-1))<shrub(3.30 mm·min^(-1)).The correlation between K_(s) and organic matter,bulk density,and soil particle composition,varied across different land use patterns.A multiple stepwise regression model showed that silt,coarse sand,bulk density,and organic matter,were key predictive factors for the K_(s) of farmland,tree,shrub,and grassland,in the MUSL.Discussion The vertical distribution trend for K_(s) in farmland is known to be predominantly influenced by cultivation,fertilization,and other factors.The general aim is to improve the water-holding capacity of shallow soil on farmland(0-30 cm in depth)to conserve water and nutrients;research has shown that the K_(s) of farmland increases with soil depth.The root growth of tree and shrub in sandy land exerts mechanical force on the soil due to biophysical processes involving rhizospheres,thus leading to a significant change in K_(s).We found that shallow high-density fine roots increased the volume of soil pores and eliminated large pores,thus resulting in a reduction in shallow K_(s).Therefore,the K_(s) of tree and shrub increased with soil depth.Analysis also showed that the K_(s) of grassland did not change significantly and exhibited the lowest mean value when compared to other land use patterns.This finding was predominantly due to the shallow root system of grasslands and because this land use pattern is not subject to human activities such as cultivation and fertilization;consequently,there was no significant change in K_(s) with depth;grassland also had the lowest mean K_(s).We also established a transfer function for K_(s) for different land use patterns in the MUSL.However,the predictive factors for K_(s) in different land use patterns are known to be affected by soil cultivation methods,vegetation restoration modes,the distribution of soil moisture,and other factors,thus resulting in key differences.Therefore,when using the transfer function to predict K_(s) in other areas,it will be necessary to perform parameter calibration and further verification.Conclusions In the MUSL,the K_(s) of farmland,tree,and shrub gradually increased with soil depth;however,the K_(s) of grassland showed no significant variation in terms of vertical distribution.The mean K_(s) values of different land use patterns were ranked as follows:shrub>farmland>tree>grassland;all land use patterns showed moderate levels of variability.The K_(s) for different land use patterns exhibited differing degrees of correlation with soil physical and chemical properties;of these,clay,silt,sand,bulk density,and organic matter,were identified as important variables for predicting K_(s) in farmland,tree,shrub,and grassland,respectively.Recommendations and perspectives In this study,we used a stepwise multiple regression model to establish a transfer function prediction model for K_(s) for different land use patterns;this model possessed high estimation accuracy.The ability to predict K_(s) in the MUSL is very important in terms of the conservation of water and nutrients.

近地表风沙流结构对过渡带不同下垫面的响应

在塔克拉玛干沙漠南缘策勒绿洲—沙漠过渡上选取流动沙地、半流动沙地和固定沙地3个典型下垫面,利用梯度集沙仪测定其近地表10cm的风沙流结构。结果表明,流动沙地地表0~1cm的沙粒百分含量随着风速的增大而减小;2~10cm的沙通量随着风速的增大其百分含量增加,1~2cm的沙通量存在一个稳定层,幂函数、指数函数和对数函数均能较好地反映其沙通量垂直分布特征,并可以利用风沙流结构来判定地表的蚀积状况;半固定和固定沙地地表由于受到植被盖度影响,其风沙流结构特征表现为近地表0~1cm沙通量较流动沙地少,2~10cm的沙通量百分含量较多,且每层沙通量与风速的相关性较差,稳定层在植被盖度的扰动下抬高或者消失,对数函数能较好地反映其风沙流结构特征,地表蚀积状况不可用现存风沙流结构地表蚀积公式来判定。

Numerical investigation of particle saltation in the bed-load regime

This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of 2–3 layers of densely packed spheres.In this study,we combined three the state-of-the-art technologies,i.e.,the direct numerical simulation of turbulent flow,the combined finite-discrete element modelling of the deformation,movement and collision of the particles,and the immersed boundary method for the fluid-solid interaction.Here we verify our code by comparing the flow and particle statistical features with the published data and then present the hydrodynamic forces acting on a particle together with the particle coordinates and velocities,during a typical saltation.We found strong correlation between the abruptly decreasing particle stream-wise velocity and the increasing vertical velocity at collision,which indicates that the continuous saltation of large grain-size particles is controlled by collision parameters such as particle incident angle,local rough bed packing arrangement,and particle density,etc.This physical process is different from that of particle entrainment in which turbulence coherence structures play an important role.Probability distribution functions of several important saltation parameters and the relationships between them are presented.The results show that the saltating particles hitting the windward side of the bed particles are more likely to bounce off the rough bed than those hitting the leeside.Based on the above findings,saltation mechanisms of large grain-size particles in turbulent channel flow are presented.

Heat Loss from Buried Vertical Plate with Assigned Temperature Distribution

Thermal losses for a buried vertical thin plate can be expressed as a function of the assigned temperature distribution,the medium conductivity and the geometrical properties that describe the model. When the geometricalproperties reduce to one, the plate-ground thermal resistance can be expressed regardless of plate dimension, dependingonly on temperature distribution given at surface plate and its temperature difference with medium.