Ecological Study Based On Plant Physiology Of Bioretention And Functional Study Based On Clogging Regularity Of Growing Media

Bioretention,as a typical form of green infrastructure,has made important contributions in reducing urban runoff and alleviating urban non-point source pollution.This study evaluated and analyzed the operation effect of bioretention facilities from the aspects of "ecological " and "functional".In addition to the regulation effect of water quality and quantity of bioretention,the impacts of road runoff on plant physiology and ecological risks accumulated by heavy metals in the substrate were emphatically analyzed.This study also took the penetration performance of bioretention as the starting point and clogging as the control critical point,analyzed the factors that affect the penetration performance,evaluated the operation effect of bioretention,estimated the critical life of the blocking and provided operation and maintenance nodes.The theoretical basis provided technical support for achieving the goals of aquatic ecology and water environment in sponge cities.(1)The type of substrate affected the reduction effect of bioretention on different pollutants.The water retention rate of topsoil + sand(SS),topsoil + sand + humus(SSH),and topsoil + sand + vermiculite + perlite(SSVP)was between 73.0% and 79.9%.SSH was the best,followed by SSVP,and finally SS.For COD and N elements,the concentration reduction rate of adding humus and perlite vermiculite media was slightly lower than SS,but it effectively improved the concentration and quality reduction effect of heavy metals.Among them,the humus adding device was the best,followed by SSVP.The removal effect of each device on heavy metals was Zn>Cd>Cu> Pb.In view of the characteristics of high frequency and large proportion of small rainfall in Beijing area,SSH and SSVP can significantly improve the removal rate of COD,N element and heavy metal accumulation load.(2)The effect of runoff on physiological indexes of plants shows obvious inter-species difference.Herbs,by contrast,may be more susceptible to runoff and rainwater.Among them,heavy metals were more likely to accumulate in Liriope and Goosegrass.Stormwater runoff only significantly affected the membrane permeability of Ligustrum vicaryi in the SS.However,during the experiment,the runoff of the road did not cause obvious apparent difference to the plants.(3)Through the statistics of rainfall data and runoff water quality characteristics in Beijing for 30 years,the inlet water volume,inlet water interval and simulated inlet water concentration were designed in accordance with local hydrological characteristics.After four months of experiments,the pollution degree caused by the accumulation of heavy metals in various media was at the level of no pollution or slight pollution.(4)The study on the factors affecting the permeability of bioretention shows that the planting of Iris tectorum Maxim and Iris lactea improved the permeability of the bioremediation facilities,among which the root system of Iris tectorum Maxim had the root characteristics of thick and long taproot and less transverse root such as fibrous root,and had stronger maintenance capacity of permeability.The submerged zone reduced the initial permeability coefficient of the system and increases the risk of clogging.The addition of fermented sawdust,perlite or vermiculite improved the initial permeability,but also reduced the anti-clogging ability of the device,which was susceptible to the influence of incoming particles.However,from the absolute value of saturated permeability coefficient,high initial permeability coefficient was very necessary.The smaller matrix thickness was helpful to improve the initial permeability coefficient of the system,but it also had poor anti-clogging performance.The surface layer of matrix was more easily blocked.The hydraulic load had little effect on the permeability of the system.According to the regression analysis,the order of strength of the factors that affect the decreasing degree of the permeability coefficient of the plant was as follows: intake particle concentration> plant species> with or without submerged area> device initial permeability coefficient.When the critical value of permeability was 50 mm/h,the operating life of each device varied from 0.5 to 17.11 years.(5)Studies on the permeability of bioretention in reducing pollutant loads show that after the clogging,each device had a better concentration reduction rate for SS and COD,and also improved the concentration reduction rate of some devices for TN.However,the phenomenon of clogging also leads to the increase of overflow flow and the decrease of water retention rate of some devices.As a result,the pollutant load reduction rate was subject to the relative sizes of the water reduction rate and the concentration reduction rate,and there was no uniform phenomenon for pollutant load reduction of each device.