| The rapid development of the city has a significant impact on the urban ecological environment,especially on the surface water environment.Polycyclic aromatic hydrocarbons(PAHs,Polycyclic Aromatic Hydrocarbons)are a variety of polyphenylene cyclic hydrocarbons with volatile,aromatic and stable physical and chemical properties.PAHs have become a threat to human health because of their high stability,carcinogenicity and teratogenicity.Urban rainfall or rainstorm will scour the suspended polycyclic aromatic hydrocarbons(PAHs)into the urban water body,which will cause great harm to the urban water environment.Urban forest ecosystem has significant ecohydrological effect on rainfall and PAHs.In particular,the adsorption storage and filtration effect of forest soil can effectively reduce the amount of water infiltrated into runoff and water pollutants,especially the reduction or removal effect of PAHs.Therefore,the ecological and hydrological effects of two forest types on rainfall permeable water and PAHs were studied by taking the evergreen broad-leaf secondary forest and conifer broad-leaf mixed forest in Maofeng Mountain,Guangzhou as the object.Based on the continuous observation of forest hydrological and ecological positioning station,the relationship between relative rainfall interception,filter energy and quantity of forest soil was revealed by comparing two soil depths(30 cm,60 cm)with the corresponding treatment.To explore the effect of forest soil on PAHs reduction and removal.The results of this study can deepen the understanding of the purification environmental function of urban forest ecosystem and play a good guiding role in the directional cultivation of urban ecological forest community.After more than 15 heavy rain tests a year,the main conclusions are as follows:(1)The soil water holding capacity of secondary evergreen broad-leaf forest(EGBLF)in Maofeng Mountain of Guangzhou was stronger than that of secondary conifer and broadleaved mixed forest(CBLF),and the rainstorm ecohydrological effect of EGBLF ecosystem was significant.The osmotic water intercepted by the 30 cm and 60 cm deep soil layers of the CBLF accounted for 41.5% and 39.3% of the corresponding cumulative rainfall(634.2mm),respectively,which was 17.8% and 19.2% lower than the EGBLF t.The 30 cm deep soil layer and the 60 cm deep soil layer of the CBLF effectively retained 41.5% and 39.3% of the precipitation,while the corresponding increase rate of the EGBLF was 17.8% and 19.2%,respectively.According to the 60 cm osmotic response rate of soil layer,the permeability of the 60 cm layer of EGBLF soil to heavy rain and heavy rain reached 49.6% and 40.0%,respectively,which was 10.8% and 20.7% smaller than the corresponding CBLF.That is,the rainstorm ecological hydrological effect of the EGBLF ecosystem is extremely significant.(2)According to the same soil depth seepage water,the EGBLF can reduce PAHs in rainfall better than the corresponding CBLF.The content of rainfall permeable water in 30 cm,60 cm deep soil layer of secondary evergreen broad-leaf secondary forest and conifer broad-leaf forest mixed forest was compared with the concentration of PAHs component in rainfall.Concentration removal of main carcinogens,Benzo(g,hi)perylene(BPE),Benzo(k)fluoranthene(BKF),Benzo(b)fluoranthene(Bb F),Fluoranthene(FLT),Benzo(a)pyrene(Ba P),Indeno(1,2,3-cd)pyrene(IPY)from forest canopy to 60 cm soil layer in rainfall environment;The concentration of Bb F in rainfall decreased by 52.14%,Ba P concentration decreased by 24.41%,FLT content decreased by 19.26%,BKF concentration decreased by 9.93%,IPY decreased by 4.99%,and Bb F concentration decreased by 0.68%.However,the canopy to 30 cm soil layer of evergreen broad-leaf forest only reduced the concentration of BPE,BKF,Bb F,IPY in carcinogens in rainfall.The concentration of 13 PAHs components in seepage water of 30 cm soil in conifer and broad-leaved mixed forest was higher than that in corresponding rainfall,while the concentration of permeable water in 60 cm soil in forest was lower than that in corresponding rainfall content.(3)The content of polycyclic aromatic hydrocarbons(PAHs)in seepage water produced by natural rainfall was different between conifer and broad-leaf forest and evergreen broadleaf forest by leaching and sterilizing with 0.05% glutaraldehyde solvent.After the sterilization of evergreen broad-leaved secondary forests,the ability to reduce polycyclic aromatic hydrocarbons in rainfall was significantly reduced.After the coniferous and broadcrossing secondary forests are sterilized,the ability to reduce polycyclic aromatic hydrocarbons in rainfall is enhanced.The content of Naphthalene(NAP)in osmotic water of conifer and broad-leaved mixed forest 30 cm soil treatment group was significantly lower than that of 30 cm soil control group(P < 0.01).There was no significant difference in the contents of 16 polycyclic aromatic hydrocarbons(PAHs)in osmotic water of coniflower and broad-leaved mixed forest 60 cm soil treatment group.The content of Indeno(1,2,3-cd)pyrene(IPY)in evergreen broad-leaf forest 30 cm soil treatment group was significantly higher than that in the control group(P < 0.05),and the content of other individual components also increased to a certain extent.There was no significant difference in the contents of 16 polycyclic aromatic hydrocarbons(PAHs)between the 60 cm soil treatment group and the control group,but the contents of Anthracene(ANT),Chrysene(CHR),Indeno(1,2,3-cd)pyrene(IPY)in the treatment group were higher than those in the control group. |
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