Distribution Of Methylmercury And Microbial Methylation In Main Mangrove Wetlands Of China

Mercury,methylmercury and environmental factors had been investigated to study distributions of the methylmercury and mercury methylation in the sediments and plants from 6 main mangrove areas of Hainan,Guangdong.Guangxi,Fujian of china.This paper focus on the following topics:(1)distributions of total mercury and methylmecury in the sediments of mangrove wetland.(2) Transfer and transformation of methylmercury in mangroves.(3) The effects of main geochemical factors on the distribution of methylmercury in sediments.(4) Vertical and horizontal distributions of the number of micro-organisms(total micro-organisms and SRB) in mangrove sediments.(5) Physical and chemical factors effect on mercury methylation.Some conclusions were drawn as follows:1.Total mercury and methylmercury concentrations were not consistent in sediments. Data collected in this study showed that mercury pollution level of mangroves in china was in the order of Fujian>Hainan>Guangdong>Guangxi.Methylmercury concentration of the sediments in different areas was in the order of Leizhou(LZ)>Daguansha(DGS)>Futian(FT)>Dongzhai(DZ)>Fugong(FG)>Gaoqiao(G Q)>Sanya(SY).Mercury and organic carbon inputed from industries and agriculture may increase methylmercury level.Low total mercury concentration related to high methylmercury ratio that may mainly contribute to the difference of sediment size.2.Methylmercury content of mangroves at the range of 0.222～1.755ng/g,of which the highest concentration showed up in Rhizophora stylosa in Fugong and the lowest in Aviccnnia marina in Dongzhaigang.Methylmercury contents in various organs of mangroves related to their physiological features,especially in response to salt.In addition the methylmercury content of sediments is also one of the major reasons effecting the accumulation of methylmercury in the plants.3.Using DAPI fluorescence staining method in the determination of sediment total number of micro-organisms,data showed that the contents,form the highest to the lowest,were Fugong>Sanya>Gaoqiao>Dongzhaigang>Futian>Daguansha.The total bacterial contents at the range of 2.44×10¹⁰-1.91×10¹¹ cfu/g dw.The strength of various environmental factors effecting on micro-organisms was no significant differences.Using culturing and MPN method to count the number of SRB in sediments,the horizontal dstribution of SRB content was in the order of Futian> Fugong> Dongzhaigang> Sanya> Gaoqiao> Daguansha.Economic development brought high concentration of organic matter to the sediments by the wastewater, which is the main reason for higher content of SRB.The types of surface sediments also had a great impact on the SRB distribution.The contents of SRB in profile samples had two peaks in every area,the first peak related to higher organic matter content at the surface sediments,and the second peak mainly related to the impact of root system of mangroves.4.Correlation Analysis found that the number of microbes and concentrations of methylmercury showed a significantly positive correlation while the number of SRB and methylmercury content showed a significantly negative correlation.This indicated that SRB was not the main methyling micro-organism of mangrove estuary.And there may be other species of micro-organisms on the role of mercury methylation.5.Correlation Analysis between envrionmental factors and methylmercury in profile sediments of Fugong found that various environmental factors are all related to methyl mercury content with good correlations.Salinity and MeHg showed significantly positive correlation(p<0.01,N=15);THg,S showed significantly positively correlation with MeHg(p<0.05,N=15);pH showed significantly negatively correlation with MeHg(p<0.05,N=15).