| Polycylic aromatic hydrocarbons (abbr. PAHs) are a large group of organic pollutants, which are composed of structurally similar multiple benzene rings, and widely distributed in the environments. Environmental scientists all over the world assign the highest possible importance to PAHs for it's potential damage to human health and eco-environments.Camphor (Cinnamomum camphora (L.) presl) is one of the most important kinds of the evergreen tree species widely distributing in the subtropical region of China, and the national peculiar species for timber and economy. Camphor plays an important role in protecting regional environments for its high multi-utility of resistance to dangerous gases, prevention and detention of smut, clearing the air, reduction of noise, and tolerance to pollution. And it is therefore commonly used as excellent greenery tree species in southern China.In this study, the modern analysis instrument, gas chromatograph, was employed to investigate the categories and concentrations of PAHs in the plants and soil of camphora forest plantations at the suburb of Zhuzhou city, Hunan Province. Furthermore, we paid more attention to all-way through monitoring of changes of PAHs in concentrations during the forest hydrological processes with the long-time located forest research methods. The aim of this study is to explore the characteristics of transportation, adsorption, and transformation of PAHs in the comphora forest hydrological processes. And the main result is as the following.The concentrations of PAHs in different organs of overstory trees could be ranked in the following order: bark (8641μg.kg~-1) > fruit (7520μg.kg~-1) > root (7115μg.kg~-1) > branch (5352μg.kg~-1) > leaf (4481μg.kg~-1) > stem (2843μg.kg~-1). The concentrations of PAHs varied with different compartments of the plantations, 5995μg.kg~-1 for overstorey trees, 363μg.kg~-1 for herbal plants, 245μg.kg~-1 for understorey shrubs plants, 9235μg.kg~-1 for litter, and 1466μg.kg~-1 for soil. The PAHs concentrations in the soil decreased by over 1 times contrast to that in the soil of a bare land. At the same time, the PAHs concentrations in both throughfall and surface runoff was lower than that in the precipitation, whichindicates that PAHs were absorbed and transformed by the forest hydrological processes.The accumulation of PAHs in the comphora plantations varied with compartments of the ecosystem. The total amount of PAHs in the system was 575.02 g/hm2, and that in the overstory by 450.99 g/hm2, roots by 143.08 g/hm2, branches by 119.12 g/hm2, leaves by 21.06 g/hm2, respectively. Based on the accumulation data, these organs can be ordered in quantity as root (24.9%) >branches (20.7%) >stems (18.6%) >barks (10.5%) >leaves (3.7%) .The understory also plays an important role in accumulation of PAHs in the ecosystem. The amount of PAHs was 114.65g/hm2 in the litter layer, gaining a ratio to the whole plant system by 19.9%, and 1.09g/hm2 in the shrubs with a ratio by 0.2%. The total accumulation amount of PAHs in the comphora plantations was 24.01 g hm^yr"1, which suggested a relatively high ability to accumulate PAHs in the environment.However, the ability may change with different aspect of slope, the amount of PAHs was 804ug-kg"1for south slope, and 1018ug-kg"' for north slope, respectively. The average was 911ug-kg'1. PAHs were mainly distributed in the surface soil layer. The amount was 1688ug-kg"' in the layer with a depth of 0-30cm, and 397ng-kg"1 in the depth of 30cm, respectively. And both categories and amount of PAHs were less in the depth under 45cm than that in the depth above 45cm. There was a significant correlation between soil organic content and PAHs concentrations.Assessment of 10 types of PAHs was given based on these targets set in the standard of Netherland. The main components of PAHs were benzanthracene(BaA), benzopyrene(BaP) (IiP), which were all beyond the standard concentrations, especially for BaA, IiP. In the bare lands, the main components beyond the standard were anthracene(Ant), fluoranthene(Fla^ BaAN benzofluoranthene(BkF), especially Fla, BaA.There were 10 types of PAHs measured in the precipitation outside the stands, the total concentration was 288.662ng-L"', in which the concentration of Ant and BaA was 210.05ug-L"1, and 52.296iJ.gT1, respectively; the concentration of BaP was 0.336ug-L"\ which was lower than the formers.PAHs in precipitations were intercepted and adsorbed by the canopies of camphorastands, so the concentrations (lOl^Olug-L"1) in the throughfall were lower than that in. precipitations outside of stands. 5 tpyes of PAHs were measured in stem flow, and totalamount was 82.069u.g-L'1. Eluviation of PAHs in canopies by rainfall was significant,which resulted in an increasing concentrations in precipitations inside of stands, such as B^ D^ IiP. According to eluviation coefficients in throughfall, the rank of components of PAHs can be listed as BaP >IiP >DaA >Ant >Phe >BaA. Whileas the sequence of eluviation coefficients for stem flow was BaP >IiP >DaA >BaA >Ant.There were measured 5 tpyes of PAHs with the total concentrations only by 36.866 (ig-L"1. According to the concentrations of components, it could be ranked as Ant > BaA > DaA > IiP > BaP. PAHs input the system were reduced by runoff through ground covers and soils, and purified by leaching through compartments of stands to some extent.The results showed that camphora plantations may play an important role in absorption, transportation, and degradation of PAHs, which could provide a scientific basis for more reasonable controls of PAHs, management of urban forest construction, and effective environmental measurements. |
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