Experimental Study On The Effects Of Pollutant Accumulation In Bioretention System On Microbial Community Structure

Bioretention technology has a good effect on non-point source pollution control by controlling runoff pollution,reducing runoff volume and peak flow.In the meantime,while people excessively pursue the natural accumulation and the total amount control of stormwater runoff,they change the underlying surface and pollution characteristics of stormwater runoff.Runoff pollutants from the traditional mode on one side,gradually converted to centralized infiltration,most of the pollutants were adsorbed by the upper media,and gradually reached the state of saturation.These pollutants will be transferred to the internal media and continue to accumulate,not only affect the normal operation of the system,and even to the nearby soil,groundwater security problems.Combined with field monitoring and test research,this study uses traditional and modified media bioretention system as the research object,evaluates the existing bioretention system pollution risks by several heavy metal pollution index methods,and qualitative analysis of runoff pollutants within the facility short-term accumulation characteristics and influence on the enzyme activities and microbial community structure.The main research results are as follows:(1)During the short term operation of bioretention system,heavy metal pollution is relatively slight,among which cadmium pollution is the most serious;from view of different facilities,the bioswale for treating road rainwater is more seriously polluted than other facilities.(2)The characteristics of physical and chemical properties of media in monitoring facilities and experimental facilities are as follows:The physical and chemical properties of media in bioretention system in actual operation are greatly affected by external factors,especially water content and heavy metals;The change of total nitrogen also varies with the difference of sites.Total organic carbon decreases in non-flood season;The total phosphorus content decreased at the in-situ point,increased in the non-flood season,and decreased after the flood season.The variation trend of ammonia nitrogen and nitrate nitrogen was consistent with the total phosphorus in the biological detention facility.After water distribution experiment,the moisture content showed a trend of planting soil>BSM+5%WTR>BSM.The content of nitrogen,total organic carbon and total phosphorus increased.Cadmium and copper are increasing on the whole,while zinc content is decreasing in#5 and#6.(3)After the water distribution test,the amount of acid phosphatase decreased,the activity of urease increased,and the changes of sucrase showed different rules,but the overall level was similar.The changes of dehydrogenase may be affected by the inlet water quality,and the change trend was opposite in#1?#3 and#4?#6 filters.Urease was affected by most factors,pH had little influence on enzyme activity,and total organic carbon,total nitrogen and total phosphorus had great influence on enzyme activity.Among the three heavy metals,copper has little negative influence on enzyme activity,while zinc and cadmium have inhibitory effect on soil enzyme activity.(4)It can be seen from the two parts of field monitoring and small test that after the short-term runoff and rainwater entered the facility,the species of dominant bacteria in the microbial community did not change.Proteobacteria are the dominant bacteria in biological retention facilities,Acidobacteria is the dominant bacteria in the in-situ point.At the level of genus,the relative abundance of genus>1%in the samples collected three times by on-site monitoring facilities decreased from 21 species to 17 and 16 species.Pseudomonas,Massilia,Bacillus,and Reyranella were affected by the influent water quality.(5)The relative abundance of microbial phylum level and environmental factors analysis and combined with packing the physical and chemical properties of RDA and relative abundance of heavy metals and microbial belongs to the level of Pearson correlation analysis results show that the pH influence degree of microbial community structure is not clear,total organic carbon,total phosphorus and water content is greatly influenced by three factors,heavy metals have an effect on microorganism,different influence degree of heavy metals,the same kind of heavy metal different effects on different microbes.