Ecological Effects Of Pahs On Mangroves And Soil

Polycyclic aromatic hydrocarbons(PAHs) are persistent organic pollutants(POPs) commonly occur in the air or on the earth, many of which are identified as either teratogenic or carcinogenic or mutagenic to human beings, thus, have caused worldwide concern. Driven by economic development and globalization, PAHs concentration has been surged in the environment, especially in Mangroves. Because mangroves usually have large area of sticky sediments which contain vast amount of organic matter or humus, and the particles of the sediments are very tiny, PAHs in mangroves are easy to stagnate and accumulate. Hence, the subject of PAHs reduction and restoration becomes one of the research hotspots and difficulties. This article aims at investigating how the growth of two kinds of mangroves, namely Kandelia obovata and Aegiceras corniculatum, are influenced under the pollution of two typical PAHs, Phe and Pyr, both at 100mg?kg-1, through 60-day plantation. Also, soil physicochemical property, soil enzyme activity and the PLFA(Phospholipid Fatty Acid) of the soil microbiota in this process were analysed, meanwhile, the removal rate of PAHs at 60 th day was detected. The results were as follows: 1. Removal of Phe and Pyr and their influence on the growth of K. obovata and A. corniculatu.After 60 days, the removal rate of total PAHs in soil planted with K. obovata and A. corniculatu were 35.8% and 36.6%, respectively, both significantly higher than soil without mangroves, but no significant difference was found between the two mangrove plant species. The results showed that K. obovata and A. corniculatu exhibited low efficiencies in removing PAHs. Height, ground diameter and leaf number of these two mangrove plants were found no significant difference towards time while Chlorophyll content was significantly increased as time passed, suggesting that 100 mg?kg-1 Phe and Pyr do not have any toxic effect on them. 2. Effects of Phe and Pyr on soil physicochemical property.p H of the contaminated Soil was significantly higher than the uncontaminated, while soil conductivity resulted the opposite way, indicating that PAHs might have inhibited the H+ and salt in soils. The content of total phosphorus and available phosphorus in soil polluted by PAHs was significantly higher than those in uncontaminated soil, suggesting that phosphorus biochemical process was stimulated by PAHs. On the contrary, the content of ammonia nitrogen and potassium nitrate in contaminated soil was significantly lower than that in clean soil, the effectiveness of nitrogen cycle may have been weaken because of PAHs. 3. Effects of Phe and Pyr on activity of soil enzymes.PAHs enhanced aryl sulfatase and phosphatase’s acitivity in soil but weakened cellulase and β-Glucosidase, suggesting that these four kinds of soil enzymes were closely related to PAHs degradation. With time growing, the activity of cellulase had decreased while β-Glucosidase had inceased. 4. Effects of Phe and Pyr on PLFA(Phospholipid Fatty Acid) of the soil microbiota.Phe and Pyr stimulated the amount of the fatty acid represents for total microbiota, total bacteria, fungus and actinomyces in contaminated soil, the difference of the abundance of these biomarkers between contaminated soil and clean soil were all significant. Gram negative bacteria in contaminated soil were richer than that in clean soil, proposing that gram negative bacteria were important to PAHs removal. The 18:1ω9t/18:1ω9c rate in contaminated soil was higher than that in clean soil, means contaminated soil was more suitable for microbes living. 5. Comparison between rhizosphere soil and bulk soilThere was no significant difference between rhizosphere soil and bulk soil in soil physical chemical properties and PLFA contents.In conclusion, K. obovata and A. corniculatu were not good at PAHs removing. Phe and Pyr of 100mg?kg-1 did not show toxic effect to either of them, but had impact on soil physical chemical property, soil enzyme activity and Soil microbes. There was no significant difference between rhizosphere soil and bulk soil in all indexes.