Explore The Migration And Transformation Of Nitrogen In Grassed Paving System

The grassed paving system is a typical LID measure to alleviate the problem of urban stormwater runoff by reducing impervious area of the city,and it has been increasingly applied.As the grassed paving system is a complex system of plants,soil,and filler structures,a series of physical and biochemical actions occur when the runoff rain contaminants enter the system,and pollutants are converted into three systems.Therefore,it becomes more difficult to study the mechanism of pollutant removal in the grassed paving system.This project has experimened the removal effect of run-off rainwater pollutants.The ¹⁵N isotope tracing technique was used to explore and quantify the migration and transformation of nitrogen in the grassed paving system.1)Experiments were conducted to study the effect of planting type,temperature,soil pH,carbon source,and rainfall interval on the removal of nitrogen,phosphorus,and COD pollutants from runoff rainwater.The results showed that the grassed paving systems with three plants including Zoysia matrella?Z?,Eleusine indica?E?and Liriope graminifolia?L?,were good for removing NH₄⁺-N,NO₃^--N and TN,and from rainfall runoff.The best way to remove phosphorus is to plant L,Z is the next,and E is the worst,and there was no significant correlation between COD removal and plant species.The system of planting Liriope graminifolia was better at denitrification and COD removal at 27°C than at 22°C,but there was no significant correlation between removal of TP and temperature.When the soil pH range was 6.40⁸.24,with the increase of soil pH,the system of planting L had worse effect on NO₃^--N and TN removal,and the better the removal effect of COD,the worse the adsorption effect on phosphate.With the increase of C/N,the removal of TP and COD by the system of planting L was better,but the removal of total nitrogen did not change significantly.When the rainfall interval was 5 days,the grassed paving system could respectively remove70%,80%and 80%of runoff TN,TP and COD in 17 detention days.2)In this experiment,we studied the effects of the soil adsorption,plant uptake,microbial fixation,nitrification,denitrification and dissimilatory nitrate reduction to ammonium process?DNRA?on nitrogen removal under different influent C/N ratios by using¹⁵N isotope tracing technique in a simulated grassed paving system.The migration and transformation of nitrogen were quantitatively analyzed.The results showed that the removal rate of NH₄⁺-N,NO₃^--N,TN and COD in rainwater were 85%,96.3%,85.8%and 77.5%,respectively.The adsorption of soil inorganic particles,plant uptake,microbial assimilation and nitrification are the main factors during 0⁵d.The denitrification reaction is predominant during 5¹2d.The nitrification and denitrification reactions were significant during 12²0d.Under low C/N ratio,DNRA effect and denitrification were weak and nitrification was strong.With the increase of C/N ratio,the nitrification reaction was weakened and DNRA effect and denitrification were enhanced.C/N ratio had no significant effect on the adsorption of soil inorganic particles,plant uptake and microbial assimilation.3)The purpose of this paper was to study the effects of the N transformation and transportation processes under different soil pH,plant species and rainfall intervals by using¹⁵N isotope tracing technique in a simulated grassed paving system,and to quantify the processes in it.The results showed that the grassed paving systems with three plants including Zoysia matrella?Z?,Eleusine indica?E?and Liriope graminifolia?L?,were good for removing NH₄⁺-N,NO₃^--N,TN,and COD from rainfall runoff.However,there was no significant difference in TN removal among these three-plant species and a certain soil pH.The experiment showed that when the rainfall interval was 5 days,the grassed paving system could remove 65.8%⁷6.8%of runoff TN in 17 detention days.The N conversion was dominated by soil abiotic fixation,plant uptake,microbial assimilation,and nitrification during 0⁵d.While the main N reactions were mainly through denitrification and DNRA during 5¹4d.4)High-throughput sequencing technology was used to study the community structure and diversity of microorganisms during removal of NH₄⁺-N,TN,TP,and COD in rainwater runoff by the grassed paving system.The results showed that in the experimental stage,the five dominant genera with significant increase in content all had the functions of denitrification and dephosphorization,and the change and concentration of microbially dominant genus showed a positive correlation with the concentration changes of NH₄⁺-N,TN,TP and COD.With the progress of the reaction,the diversity of microbial species in the grassed paving system of different plants is greater,and the impact of plants on microbial diversity is also more pronounced.