The Effect On Purifying PAHs And Heavy Metals From Rainfall In Evergreen Broad-leaved Forest In Maofengshan, Guangzhou

In the research, based on the technique of constrasting analyses and the measurement ofintergrated experiment, the concentrations of PAHs and heavy metal elements were measureedon precipitation, throughfall, stemflow, runoff and soil water of Maofeng evergreenbroad-leaved forest ecosystem, the 6 kinds of PAHs were that of FLV, B(b)F, B(k)F, B(a)P,B(ghi)P, I(1,2,3-cd)P, and the heavy metals were that of Cu, Pb, Cd, Zn, Hg. We concludedthe distributed characteristics and the geochemical cycle of PAHs and heavy metals, with thecomparision of clear cutting area, the purification pollutant ability of forest was illustrated withnumber. Also, the regression equations among throughfall, stemflow, interception, runoff andprecipitation were established respecticely.(1) The PAHs spectrogram in different water phases of monsoon evergreen broad-leavedforest ecosystem showed that: there 6 kinds of PAHs in precipitation, throughfall, stemflow,soil water and runoff; the peak value in the PAHs spectrogram was that: precipitation＞clearcutting runoff＞throughfall＞stemflow＞surface runoff＞soil water＞runoff; The PAHsspectrogram of soil water showed the storing mechanism of soil to PAHs.(2) The precipitation of Maofeng evergreen broad-leaved forest ecosystem in 2006 was1385.2mm,and the precipitation from April to September accounted for 77.4% of the wholeyear, the division between dry season and wet season was clear. The relations betweenthroughfall and precipitation in evergreen broad-leaved forest ecosystem were linearitycorrelation, and the equation was that: y=0.7399x-0.7177, R²=0.949; The relations betweenstemflow and precipitation were power function models, and the equation was that: S=0.0017P^1.1777, R²=0.8632; Also the relations between interception and precipitation were powerfunction models, and the equation was that: I=0.5798P^0.7836, R²=0.8438; The equationbetween runoff and precipitation was that: R=0.3683P-0.937, R²ä¸º0.9738.(3) In precipitation, the highest mean concentration of PAHs was in September, and thelowest was in April and may, and the concentrations of PAHs in dry season were obviouslyhigher than in wet season; In dry season, the concentration of PAHs in precipitation washighest, and the, the concentration in throughfall was lower than in precipitation, and the concentration in stemflow was lowest. But in wet season, the order from high to low was that:throughfall, stemflow, precipitation. In precipitation, the order of mean concentration wasFLV＞B(b)F＞I(1,2,3-cd)P＞B(ghi)P＞B(a)P＞B(k)F; and in precipitation, the relations betweenprecipitation quantum and concentration of PAHs were negative Correlation; In throughfall, theorder of mean concentration was FLV＞B(b)F＞B(ghi)P＞B(a)P>I(1,2,3-cd) P＞B(k)F; Instemflow, the order of mean concentration was FLV＞B(b)F＞B(ghi)P＞B(a)P＞B(k)F＞I(1,2,3-cd) P.(4) According to the net leaching coefficient, leaching coefficients of FLV, B(a)P was exact,and the other 4 kinds of PAH was negative, the order of storing ability of throughfall was that:I(1,2,3-cd)P＞B(b)F＞B(ghi)P＞B(k)F, and the order of storing ability of stemflow was that:I(1,2,3-cd)P＞B(b)F＞B(k)F＞B(ghi)P. The leaching ability of throughfall to FLV and B(a)Pwas stronger than stemflow, and the storing ability to the other 4 kinds of PAHs was worse thanstemflow. The concentrations of PAHs in runoff were clearly lower than in precipitation, theforest had strong storing ability to PAHs, the order of storing ability was B(ghi)P＞I(1,2,3-cd)P＞B(k)F＞B(a)P＞B(b)F＞FLV.(5) Because the adsorption of soil to PAHs, the concentration of water at soil depth of 30cmwas higher than in precipitation, with the deepening of soil, the concentration of soil waterbecame more and more lower. The deeper of the soil, the adsorption quantum of PAHs was less.It was the same with the fact that the organic carbon was less and less with the deepening ofsoil, The organic carbon was an important carrier of PAHs.(6) In precipitation, the concentration of heavy metals had no obvious law, but it wascomparatively higher from June to September. In precipitation, the order of mean concentrationof 5 kinds heavy metal was Zn＞Cu＞Pb＞Cd＞Hg, The law of concentration of heavy metalsin a year was not clear. According to the net leaching coefficient, in throughfall, leachingcoefficients of Zn, Hg was negative, and the other 3 kinds heavy metals was exact, the order ofleaching ability of throughfall in throughfall was that: Pb＞Cu＞Cd;In stemflow, the leachingcoefficients of Zn was negative, and the other 4 kinds were exact, the order of leaching abilityof throughfall in stemflow was that: Pb＞Cu＞Cd＞Hg. The concentrations of Cu,Zn, Pb in runoffwere lower than in precipitation, it showed the ability of purifying ability of forest to heavymetals. The purifying rate of forest was that: Cu (61.87%, Zn (97.71%), Pb (8.7%), and the concentration of Cd, Hg was higher in runo0ff than in precipitation, the increasing rate was6.28%(Cd),13.39% (Hg), it was because the carrying function of soil and rock.(7) Based on the study of geochemical cycle of PAHs and heavy metals, the results showedthat: the forest had strong storing ability to PAHs, the order of storing quantum to PAHs wasFLV＞B(b)F＞B(ghi)P＞I(1,2,3-cd)P＞B(a)P＞B(k)F, and the storing rate was all above 85%,and the highest rate was 98.6% (B(ghi)P). The input of 5 kinds heavy metals in precipitationwas 5810.283g/hm², and the output in runoff was 79.817g/(hm²Â·a), the year accumulatingquantm of 5 kinds heavy metals was 5730.466g/(hm²Â·a).(8) Contrasting with the clearing cutting area, the concentration of PAHs and heavy metalsin runoff of forest area was obviously lower, it was because that: in clear cutting area, theplantation and ground layer was destroyed, the purifying layer missed. So it showed that theplantation and soil of forest had strong purifying ability. The relations between storing waterand Cd, Pb storing quantum were power function models, and the equation was respectivelythat: y=0.0053x-0.0065 (R²=0.7256), y=0.0867e^0.0527x (R²=0.741).