Experimental Study On Soil Macropore Characteristics And Its Influence On Solute Transport In Coal Mining Subsidence Area

Soil water and fertilizer loss in coal mining subsidence area has become an important factor restricting land productivity in mining area,and soil macropores have a profound impact on soil moisture storage,soil water flow and solute transport.In this study,Jiuli Mountain,Jiaozuo City,a typical coal mining subsidence area,was taken as the study area.Through field investigation,laboratory analysis and simulation test,based on CT scanning technology and PCA-MLR model,the temporal and spatial variation characteristics and influencing factors of soil macropores in cultivated land in subsidence area were quantitatively analyzed.The influence of soil macropores on solute transport was clarified,which provided data support for enriching the theoretical knowledge of soil macropores and exploring the regulation and control of soil water and fertilizer resources in subsidence area.The main results obtained in this study are as follows:(1)Topographic conditions(slope orientation and slope position)in the sinkhole area have significant effects on soil physicochemical properties,with significant differences in soil water content and conductivity between slope orientations and significant differences in soil organic matter content,p H and salinity between slope positions.(2)The soil macroporosity parameters in the sink zone had significant spatial variation characteristics.On different slopes,soil macroporosity,macroporosity and pore rounding rate are significantly different;on different slopes,soil macroporosity,macroporosity,pore rounding rate and pore connectivity density are significantly different,and both macroporosity and macroporosity are highest in the middle of the slope,followed by the bottom of the slope and lowest at the top of the slope.(3)Soil macroporosity parameters in the sinkhole area have significant seasonal variation.The number of soil macroporosity,macroporosity and pore connectivity density on the south slope were higher in summer than in spring,and the number of soil macroporosity,macroporosity,pore rounding rate and pore connectivity density on the top of the slope were higher in summer than in spring.(4)The main factors affecting the characteristics of soil macropores in the sinkhole area are topographic factors and soil physicochemical properties,among which the slope direction is an important factor affecting the number of soil macropores and pore rounding rate,and its degree of influence is 40.55% and 29.96%,respectively;the soil organic matter content is an important factor affecting the soil macropores and pore connectivity density,and its degree of influence is 41.72% and 39.34%,respectively.(5)The transport parameters of nitrate ions and chloride ions in sinkhole soils have obvious spatial variability and are significantly influenced by soil physicochemical properties,in which the transport rate of chloride ions is significantly and positively correlated with soil bulk weight,and the transport rate of nitrate ions is significantly and negatively correlated with soil water content and significantly and positively correlated with soil organic matter content.(6)Soil macroporosity characteristics parameters profoundly influenced soil solute transport parameters.Soil macroporosity and macroporosity had important effects on chloride ion transport rate with 39.35 % and 35.19 %,respectively;soil macroporosity and rounding rate had important effects on chloride ion dispersion coefficient with 32.38 % and 32.03 %,respectively;soil macroporosity had important effects on average nitrate ion flow rate and dispersion coefficient with 38.78 % and 40.74 %,respectively.The degree of influence was38.78 % and 40.74 %,respectively.