| In the process of frequent rainstorm in cities,the surface runoff carries a large amount of organic pollutants into the water body,which has a significant impact on water quality.Based on Forest Ecosystem Station of the Pearl River Delta,State Forestry Administration at the Maofeng mountain located at city Guangzhou,south China: three types of urban underlying surface(grassland,cement,asphalt)storm runoff plot,the hydrologic process of rainstorm of two forest ecosystems(precipitation,throughfall,surface runoff and total runoff of forest catchment).Forest catchment locating observation and comparison test method were adopted,and used the precipitation data from the weather station nearby Longdong street,to carry out the comparative analysis of the characteristics of organic pollutant(PAHs)content in different surface runoff,and the characteristics of PAHs flux in rainstorm.the rainstorm and PAHs in storm between forest and urban area were explored,and the influence of different surface and forest to PAHs content and flux,to provide scientific basis for prevention and control of non-point source organic pollution in urban surface runoff and vegetation protection.The results are as follows:(1)In year of 2016 and 2017,the rainfall of the Maofeng forest is 2089.3mm and1673.8mm respectively,and the wushan street in urban is 18.2 percent and 23.1 percent higher respectively.In the 2 years,Maofeng forest happened 20 times rainstorm event(precipitation of 50 mm or higher),compared with the corresponding urban rainfall(Wushan street),found that small scale urban rainstorm in regional difference,what is Maofeng forest storm rainfall is mostly smaller than the urban area,.There was no significant differences between the two stations of the duration of twenty rainstorms,while the biggest rainstorm intensity of forest was less than that of the urban area.(2)There was a differences in the distribution of 16 kinds of PAH component content in rainstorm and different surface runoff.ANT was the component with high content in rainstorm and surface runoff.Thirteen types of PAH components in asphalt surface runoff were higherthan that in rainstorm and cement and grassland surface runoff.There were 14 and 13 types of PAH components in evergreen broad leaved forest and Chinese fir and broad leaved forest each higher than that in rainstorm.(3)The ?16PAHs average content load of the fourteen times of rainstorm of four kinds of surface in forest area(cement,asphalt,grassland and forest)were: asphalt surface(231.20ng·L-1)>broad-leaved forest surface(130.87 ng·L-1)>cement surface(100.42 ng·L-1)> Chinese fir and broad leaved forest surface(88.50 ng·L-1)>grassland(85.28 ng·L-1).Compared to the rainstorm concentration,the ?16PAHs in grassland and Chinese fir and broad leaved forest surface was filtered 37.2% and 34.8% each.The phytoimmobilizing rate of evergreen broad leaved forest was 3.6%,while the asphalt surface increased 70.3% of the ?16PAHs content.The asphalt surface significantly increased the concentration of PAHs in the rainstorm-surface runoff,and the grassland surface significantly reduced the runoff PAHs concentration.To PAHs concentration in forest catchment showed that: the broad leaved forest canopy decreased 13.6%PAHs on average than that in rainstorm.PAHs average mass concentration of broad leaved forest and Chinese fir and broad leaved forest ecosystem(total runoff)was 50.0% and 52.3%less than that of rainstorm each.(4)The asphalt surface showed an increasing effect on 6 typical kinds of PAH,and the increase effect of FLA,Ba P,Icd P and Bghi P was more than 140%.Grassland and cement surface had the effect of phytoimmobilizing out the 6 typical kinds of PAHs,and the phytoimmobilizing effect of grassland was better.Broad leaved forest canopy had the effect of phytoimmobilizing out the 5 typical kinds of PAHs,and its surface had the effect of phytoimmobilizing out the 3 typical kinds of PAHs.The total runoff of broad leaved forest had a good phytoimmobilizing effect,and the phytoimmobilizing effect of Bb F,Bk F,Icd P and Bghi P was more than 50%.The surface of Chinese fir and broad leaved forest had a good phytoimmobilizing effect on 6 typical kinds of PAH,and the phytoimmobilizing effect of Bb F,Bk F and Bghi P was more than 50%.The Chinese fir and broad leaved forest ecosystem had more than 50% phytoimmobilizing effect on FLA,Bk F,Icd P and Bghi P.(5)For year 2017,different underlying surface(cement,grassland,forest)of storm runoff yield rate,and two types of forest ecosystem hydrological elements analysis shows that,the sort of rainstorm runoff rate of different surface was the cement surface(77.64%)> grass surface(15.42%)> forest surface(evergreen broad-leaved forest of 8.73%,Chinese fir mixed forest is 8.73%),the cement surface runoff rate significantly greater than the grass and forest floor(P = 0.000),the grass surface runoff rate significantly greater than Chinese fir mixed forest floor(P = 0.011).There is no significant difference between the two types of forests surface runoff rate(P=0.434),and it showed that the rainstorm runoff rate of the permeable surface is much smaller than that of the impervious surface.In forest ecosystem rainstorm hydrological process,the reject rate of broad leaved forest canopy to nine rainstorm rate was14.3%,the broad-leaved forest of total runoff of storm runoff rate was smaller than Chinese fir mixed forest(runoff rate was 9.2%,20.9% respectively).(6)In 2017,the nine rainstorm ?16PAHs flux of Maofeng mountain and Wushan region were 0.98 kg·ha-1,1.17 kg·ha-1.The PAHs input to ground environment of urban was 19.4%higher than forest area.The sort of PAHs flux in different surface rainstorm runoff was the cement surface(0.56 kg·ha-1)> grassland surface(0.09 kg·ha-1)> forest surface(the broad leaved forest was 0.08 kg·ha-1,the Chinese fir mixed forest was 0.07 kg·ha-1).The effect of forest surface layer and soil layer on the decrease of the PAHs flux in rainstorm was significantly higher than that of forest canopy,and the PAHs flux in the total runoff of evergreen broad-leaved forest was lower than that of Chinese fir mixed forest.The surface of cement,grassland,and the various layers of forest(canopy and surface layer)can reduce the flux of PAHs in the rainstorm-runoff.(7)Due to the influence of traffic and pedestrian pollution,the concentration of PAHs in the rainstorm surface runoff of urban asphalt surface and cement surface is greater than that of the corresponding asphalt surface and cement surface. |
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