Study On The Leaching Characteristics Of Endogenous Nitrogen In Polymer Green Roof Matrix

The increase of the proportion of impervious area in cities leads to the increase of peak discharge during rainfall,and the problems of urban floods and water pollution caused by rainfall have become increasingly prominent.The transformation of traditional roofs into green roofs can increase urban green space,reduce rainfall runoff and alleviate urban heat island effect.However,the uncertainty of the impact of existing green roofs on the quality of stormwater runoff and the limited bearing capacity of roof structures have hindered the promotion of green roofs in China.These two problems are closely related to the green roof matrix,so a reasonable choice of substrate can better play the role of green roof.Based on the rainfall characteristics of Chongqing,a green roof model was constructed to simulate the rainfall test.Taking the polymer green roof matrix as the research object,the physical and chemical properties of the matrix were optimized.The leaching characteristics of endogenous nitrogen in the matrix under different conditions were studied,and reasonable measures were determined to alleviate the leaching of endogenous nitrogen in the matrix and reduce the pollution of the green roof leaching solution to the water environment.The main conclusions of the study are as follows:1)The study on the leaching characteristics and main influencing factors of endogenous nitrogen in green roof shows that.With the increase of rainfall intensity and the pre-drying time,the water quality of the green roof leaching solution degradations,and the total leaching loss of endogenous nitrogen increases.With the increase of the amount,the water quality of the green roof leaching solution became better,but the total leaching amount of endogenous nitrogen increased.The vegetation coverage in this experiment did not play a role in slowing down the leaching of endogenous nitrogen in the green roof.Vegetation coverage did not slow down the leaching of endogenous nitrogen from green roofs in this experiment.The main forms of nitrogen in the leaching solution are nitrate nitrogen,which accounts for 70% to87% of total nitrogen,ammonia nitrogen accounts for 12% to 28%,and other forms of nitrogen account for 0.7% to 6.3%.Rainfall is the main driving force for the leaching of nitrogen in the green roof,and it is the main factor affecting the water quality of the green roofing solution.2)The study on the changes of total nitrogen and alkali nitrogen in the green roof matrix showed that after five months of continuous simulated rainfall test,the contentof total nitrogen in the substrate was only slightly changed.After the end of the experiment,the reduction of total nitrogen in the matrix is 35.9 ~ 59.9mg/Kg.The polymer green roof matrix is a nutrient matrix with slow release type,which can provide sufficient nitrogen nutrition for the growth of green roof plants for a long time.During the test,the change of alkali nitrogen content fluctuated greatly,and the rate of reduction of alkali nitrogen content accelerated with the increase of rainfall.3)The effect of adding exogenous carbon on the leaching of endogenous nitrogen in the matrix showed that increasing the concentration of glucose solution was beneficial to reduce the leaching of endogenous nitrogen in the green roof matrix.The concentration of the glucose solution ranged from 0 g/L to 20 g/L.After eight tests,the total nitrogen leaching amount was 12.20,9.24,7.91,7.57 and 6.72 mg,respectively.This study clarified the leaching characteristics of endogenous nitrogen in polymer green roof matrix developed by ourselves at home and abroad,and found a reasonable solution to reduce matrix nitrogen leaching,which provided a reference and theoretical basis for the application and promotion of polymer green roof matrix.