Study On The Soil Preferential Flow Of Liquidambar Formosana And Quercus Acutissima Mixed Forest On Nanjing Zijin Mountain

Hydrological effect is one of the main effects of urban forest,and preferential flow pathway is an important part of urban forest hydrological cycle.In this paper,the typical vegetation of Nanjing Zijin Mountain Liquidambar formosana and Quercus acutissima mixed forest was selected as the sample plot,which was located in the urban forest ecological positioning station of Yangtze River delta in Jiangsu province.In this paper,dyeing tracer technique was selected for field measurement to explore the development of preferential flow pathway in different simulated rainfall intensity,the difference in soil characteristics between preferential flow pathway and soil matrix area,and the influence of preferential flow pathway on soil nutrient distribution.The research results are as follows:?1?The non-capillary porosity in the preferential flow pathway was significantly higher than that in the soil matrix area,and there was no significant difference in total porosity and capillary porosity.The increase of the ratio of non-capillary porosity and non-capillary porosity to total porosity promoted the development of preferential flow.There were no significant differences in sand content,aggregate R0.25%,average weight and diameter of aggregates,organic matter and inorganic carbon content between the preferential flow pathway and soil matrix area.The increase of soil initial moisture content promoted the development of preferential flow.?2?With the increase of simulated rainfall intensity,the dye coverage and the maximum depth both increased.When the simulated rainfall intensity increased from 10mm to 50mm,the maximum depth of preferential flow pathway increased from 17.72cm to 42cm.Under the three simulated rainfall intensities,the dye coverage decreased significantly with the increase of soil depth.The increase of rainfall intensity can promoted the development of the deep preferential flow pathway,so that water can flow to the deeper soil layer,but also increased the uniform infiltration of soil,the shallow preferential flow pathway would be converted into soil matrix area,but if there was a large piece of gravel in the test soil will change the preferential flow pathway or block the preferential flow pathway.?3?The higher the degree of development of preferential flow in soil,the greater the contribution rate of it to soil water-soluble organic carbon?the correlation coefficient between the staining area ratio of priority flow and the contribution rate of priority flow to water-soluble organic carbon is 0.492?.The enhanced degree of development of preferential flow pathway improved the migration ability of soil water-soluble organic carbon.The development of preferential flow caused the migration of soil total nitrogen,alkali-hydrolyzed nitrogen,total phosphorus and available potassium,resulting in uneven distribution.The contents of total nitrogen and alkali-hydrolytic nitrogen in the preferential flow pathway were significantly different from those in the soil matrix area.With the increase of simulated rainfall intensity,the development degree of preferential flow is higher,and the contribution rate of preferential flow to total nitrogen and alkali-hydrolysis nitrogen is also gradually increased.Compared with total nitrogen,the contribution rate of preferential flow to alkali-hydrolyzed nitrogen is more sensitive to the change of simulated rainfall intensity?correlation coefficient 0.502?.There was a significant difference in total phosphorus content between the priority flow area and the matrix flow area.When the simulated rainfall intensity was small and moderate,the contribution rate of priority flow to total phosphorus in soil has no significant difference among soil layers.When the simulated rainfall intensity was large,the contribution rate of preferential flow to total phosphorus in soil gradually decreases with the increase of soil depth?the contribution rate of preferential flow in soil depth of 0-10cm and 10-20cm is significantly higher than that in soil depth of 20-30cm?.The development of the preferential flow affected the distribution of total phosphorus in the soil,and the influence increased with the increase of rainfall intensity.There was a significant difference in available potassium content between the preferential flow pathway and the soil matrix area.When the simulated rainfall intensity is small and moderate,the contribution rate of the priority flow to the available potassium increases first and then decreases with the increase of soil depth.When the simulated rainfall intensity was large,the contribution rate of the preferential flow to the available potassium had no significant difference among the soil layers.The distribution and migration of available potassium were affected by the development of preferential flow,which results in uneven distribution of available potassium.?4?Index equation(y=?^a+bx+cx2) is the soil nutrient and the dye coverage matched the best model.The fitting correlations of the water-soluble organic carbon,alkali-hydrolyzed nitrogen,total phosphorus,available phosphorus in preferential flow pathway,and the water-soluble organic carbon,alkali-hydrolyzed nitrogen in the soil matrix area with the dye coverage were all greater than 0.5.