桂西北喀斯特区石灰土矿物质的空间变异特征

Spatial variation of limestone soil minerals in a karst area of northwestern Guangxi

基于整个桂西北喀斯特地区石灰土的网格取样分析,采用经典统计分析和地统计学方法,研究桂西北喀斯特大尺度区域下表层(0~15 cm)石灰土矿物质(SiO_(2)、Fe_(2)O_(3)、CaO、MgO、Al_(2)O_(3)、MnO)的空间变异特征及影响因素。结果表明:SiO_(2)含量高达55.72%,其次为Al_(2)O_(3),二者占了土壤矿物质含量的85.22%;变异系数在37.50%~71.67%之间。SiO_(2)空间自相关中等,Al_(2)O_(3)和MnO空间自相关弱,三者变程长,空间连续性好;CaO、Fe_(2)O_(3)、MgO空间自相关显著,变程短。Al_(2)O_(3)、Fe_(2)O_(3)的空间变异特征主要受海拔影响,裸岩率是影响SiO_(2)、MnO和MgO空间变异性的主要地质因子,坡度则是影响CaO空间分布的主要因素。主成分分析表明土壤矿物质是影响桂西北喀斯特区石灰土空间变异的重要因子,特别是SiO_(2)。区域大尺度下,各地质地形因子通过影响石灰土矿物质空间变异特征,从而影响石灰土的空间分布。

As extremely important components of soil and constitutors of soil skeleton,soil minerals account for over 95%of the solid mass of soil.They directly participate in the entire process of soil weathering,soil formation,and plant growth and development,impacting significantly on the internal structure,exchange capacity,and fertility status of soil.Studying the spatial distribution of soil mineral elements is of great significance for understanding and mastering soil development,physical and chemical properties,and the supply status of plant nutrients.Because of the special formation matrix and ecological environment conditions of carbonate rock—the parent material of limestone soil in karst areas,soil in karst areas presents a high degree of spatial heterogeneity.At the same time,the shortage of mineral nutrients may be an important limiting factor for the growth and restoration of vegetation in mountainous areas of carbonate rock in southwestern China.However,the spatial distribution characteristics of soil minerals on a large scale in the karst area of northwestern Guangxi are currently unclear.Clarifying the spatial variation characteristics of limestone minerals in the karst area of northwestern Guangxi can provide reference for the effective utilization of mineral resources and ecological restoration and reconstruction.In order to explore the distribution pattern of the main soil mineral components in the karst area of northwestern Guangxi and to guide vegetation restoration and ecological reconstruction in the relevant area,the spatial heterogeneity of mineral components(SiO_(2),Fe_(2)O_(3),CaO,MgO,Al_(2)O_(3),and MnO)in surface soil(0-15 cm)and its influencing factors were studied by the methods of classical statistics and geostatistics.The soil samples were collected by the grid method based on the whole karst regional scale in pumping,foundation piling,tunneling,drainage in mines,and train vibration and in the studies on karst collapse mechanisms induced by extreme climate.At present,there are about eight karst collapse mechanisms according to previous studies,such as subduction,vacuum negative pressure,pressure difference,hydraulic fracturing,gas explosion,chemical dissolution,resonance,liquefaction,etc.These processes are closely associated with changing underground hydrodynamic conditions.With a profound analysis of definitions and theoretical basis of karst collapse mechanism,this study proposes that most of the above mechanisms can be attributed to seepage deformation of soil.This means,under the action of groundwater seepage force or dynamic water pressure,some particles of the whole soil mass will move,causing deformation and destruction of soil or rock mass.During the formation of karst collapse,the action mode and direction of groundwater seepage force on karst cavities roof soil will be different because of the change of groundwater dynamic conditions.The limit equilibrium theory of soil mechanics considers the roof stability of karst cavities,which is the last stage in the development of karst collapse;the effect of surface load is only to shorten the time of ground collapse.Finally,it is pointed out that due to the practicability of water-air pressure with high-frequency sampling,accelerometer and acoustic wave sensors,the research direction on collapse mechanisms will be changed from hydrostatic pressure to hydrodynamic pressure,a challenge that should be faced with.The cavitation damage and resonance damage caused by pressure pulsation will also be the future research focus,and the corresponding critical seepage deformation or damage indicators need to be further studied the prevention and control of geological disasters of karst collapse.