| In the process of urban sponge construction,as a typical rainwater management measure,bioretention facility mainly uses soil matrix to regulate the water quantity and purify the water quality of rainwater runoff.At the same time,rainwater concentrated infiltration will also have a certain impact on the soil.Therefore,it is of great significance for the popularization and application of bioretention technology in collapsible loess area to study the reduction of water quantity and quality and the impact of rainwater infiltration on Loess under the construction mode of sponge city in loess area.In this study,the Loess Soil in Xi’an,Yan’an,Guyuan,Lanzhou and Xining were selected as the filling soil layers,and eight filter columns were built and simulated rainfall experiments were carried out to analyze the regulation effect on rainwater runoff and the distribution law of soil nitrogen content in different depths,The effects of water regulation and nitrogen removal under actual rainfall conditions were analyzed to explore the temporal and spatial changes of nitrogen content in soil.The main conclusions are as follows:（1）Through the measurement and analysis of soil physical and chemical properties in different loess areas and the construction of experimental equipment,it is clear that the Loess in Xi’an area is silt soil,and the Loess in Yan’an,Guyuan,Lanzhou and Xining areas is silt soil;Through the analysis,it is found that the collapsibility of each filter column loess is closely related to the soil specific surface area,permeability coefficient,pore volume and soil density.The collapsibility coefficient,specific surface area and soil density of class Ⅲ self weight collapsible soil in Xining area are larger than those in other areas.（2）Through nine simulated rainfall experiments,the water reduction is unstable,and the average water reduction rate ranges from 7.44%to 25.29%.The average water reduction rate of filter column 10# is the largest.With the increase of water inflow,the concentration of rainwater infiltration makes the settlement range of class Ⅲ self weight collapsible soil larger than that of class II self weight collapsible soil,and the average settlement is 67.6%larger.Hydraulic power and pollution load affect the removal rate of NO3-N and TN,but have little effect on the removal rate of NH4+-N.The total loading removal rates of NH4+-N were above 70%,and the total loading removal rates of NO3-N and TN were-29.1%～35.6%and 23.4%～78.8%respectively.（3）The results showed that the contents of NH4+-N and NO3-N reached the maximum in 0～10cm of the surface layer of the soil under the condition of small amount of water and high concentration.The average content of NH4+-N and NO3-N in 0～10cm soil was higher than that in 10～60cm soil,which had a certain accumulation effect on the surface of soil.Through the correlation analysis of soil nitrogen,inflow concentration is the main factor affecting soil NH4+-N content,and rainfall is the main factor affecting soil NO3-N content.（4）The results of rainfall monitoring of infiltration type and mixed type rainwater garden show that the infiltration type rainwater garden has better effect on water reduction.In nine rainfall monitoring,the average inflow concentrations of NH4+-N and TN exceed the limits of class IV and class V in surface water quality standards respectively.After years of operation,the mixed rainwater garden still has a high removal rate of NH4+-N in rainwater runoff,and the removal rate of NO3-N is greatly improved compared with the initial operation of the facility.（5）The results showed that there was no cumulative effect of nitrogen content in the soil of the two rain gardens and the control group,and it was greatly affected by seasonal factors.The contents of NH4+-N,NO3-N and TN in the soil were lower in January,and higher in June and October.The contents of NH4+-N and TN in the soil of rainwater garden were higher at 0～30cm and 0～10cm,and the contents of NO3-N in RD2 soil of rainwater garden were higher at 0～50cm.The contents of NH4+-N,NO3-N and TN in the surface soil of RD2 and RD3 infiltration side of rainwater garden were higher than those of control group.The concentration infiltration of rainwater runoff made the nitrogen content of infiltration rainwater garden soil larger than that of control group.According to the nutrient classification standard of the second national soil survey,the soil nitrogen content of rainwater garden for many years was statistically analyzed.The total nitrogen content of rainwater garden RD2,RD3 and control group was in the fifth,third and sixth grade standard,respectively.According to the statistics of nitrogen content of underground water quality of rainwater garden from 2016 to 2020,the nitrogen content of underground water quality of rainwater garden is grade Ⅲ standard. |
PDF Full Text Request