| In order to study the effects of different levels of human activities on heavy metals pollution in mangrove sediments in Shenzhen and Hong Kong,the core sediments of Futian mangrove,West Bay mangrove,Baguang mangrove,OCT wetland(Shenzhen)and Mai Po mangrove(Hong Kong)were selected as the research objects.The vertical distributions of physical parameters(moisture content,grain size,p H and oxidation reduction potential),organic matters(total carbon,total nitrogen and total phosphorus)and heavy metals(Cr,Ni,Cu,Zn,Pb)in sediments were analyzed.The enrichment factor(EF)and potential ecological risk index were applied to evaluate the heavy metals pollution in mangrove sediments.Combined with the Pearson correlation analysis,principal component analysis(PCA)and the historical data of industrial development in Shenzhen and Hong Kong,the factors affecting heavy metals pollution were discussed.On the other hand,as an important member of the mangrove ecosystem,the microbial community structure would be influenced by the types of ecological environment,the nature of sediments and the pollution of heavy metals.In order to understand the relationship between heavy metals and microbial community structure in the mangrove sediments of Hong Kong,the surface sediments and root sediments of Mai Po mangrove,Futian mangrove(mangrove area and tidal flat area)and Baguang mangrove were selected as the research objects.The contents of five heavy metals(Cr,Ni,Cu,Zn,Pb)in sediments were measured.The 16 S r DNA V4 hyper-variable region of sediments microbial was sequenced by the second generation high-throughput sequencing technology(Illumina Hi Seq).Based on the OTUs annotation and classification,diversity analysis(Shannon-Wiener index),cluster analysis and Spearman correlation analysis,the main microbial community in different types of mangrove sediments was analyzed.Also the relationship between diversity of microbial community with heavy metals contents was discussed.The main results of this study are as follows:1.Clay was the dominant component in Mai Po mangrove and Futian mangrove sediments.Silt and sand were the dominant components in West Bay Mangrove sediments.Sand was the dominant component in Baguang mangrove sediments.The sediments of Futian mangrove,Mai Po mangroves,West Bay mangrove and Baguang mangrove were acidic,slightly alkaline,slightly acidic and neutral,respectively.The vertical distributions of organic matters in Mai Po mangrove,Futian mangrove and Baguang mangrove sediments were relatively stable,while that in West Bay mangrove and OCT wetland sediments fluctuated greatly.The organic matters contents of OCT wetland and Baguang mangrove sediments were higher,while that in Mai Po mangrove and Futian mangrove sediments were lowest.2.The results of potential ecological risk index showed that the order of pollution levels of five mangrovse was as follows: OCT wetland > Mai Po mangrove > Futian mangrove > West Bay mangrove > Baguang mangrove.Although the single potential ecological risk of heavy metals in five mangrove sediments was different,the potential ecological risk of Cu was the largest.The contents of Cu and Zn in sediments of Mai Po mangrove,Futian mangrove and OCT wetland were significantly higher than those of most mangrove areas at home and abroad.3.The main nature factors affecting the heavy metals contents of mangroves in Shenzhen and Hong Kong were grain size composition and moisture contents.Organic matters and p H were also important factors affecting heavy metals contents,while the effect of oxidation reduction potential on heavy metal contents was not significant.The heavy metals in Futian mangrove were mainly influenced by grain size composition,moisture contents and p H.Mai Po mangrove and West Bay mangrove were affected by grain size,moisture contents,p H and organic matters contents.Baguang mangrove and OCT wetland were mainly affected by organic matters contents.4.Heavy metals pollution in mangroves was mainly caused by human activities in Shenzhen and Hong Kong.The emission of effluent and domestic sewage,the development of sea and road transportation,tourism,agriculture and aquaculture would cause heavy metals pollution to mangroves.The heavy metals pollution caused by industrial development was more obvious.The heavy metals pollution of mangrove sediments in Shenzhen and Hong Kong increased in varying degrees from 1990 to 2010,in which the West Bay mangrove,Baguang mangrove and OCT wetland increased more significantly.From 2010 to 2015,heavy metals pollution of mangrove sediments in Shenzhen and Hong Kong was stable,or even decreasing,such as the West Bay mangrove and Baguang mangrove.Although the rapid development of industry would bring heavy metals pollution to the environment,there might be some balance between the economic development and the environment.The rational adjustment of the urban industrial structure could not only promote the economic growth,but also benefited the environmental protection.5.At the phylum level,the dominant bacteria of the surface sediments and root soils in mangrove of Shenzhen and Hong Kong were Proteobackteria,Chloroflexi,Actinomicrobial,Bacteroidetes,Firmicutes,etc.At the class level,Gammaproteomicrobial,Alphaproteomicrobial,Deltaproteomicrobial,Anaerolineae,Betaproteomicrobial were predominant.6.The microbial communities of surface sediments and root soils had significant genetic differences.Although the results of microbial diversity analysis showed that there were no significant correlations(P>0.05)between the microbial communities diversity and heavy metals pollution under different pollution conditions,Spearman correlation analysis showed that heavy metals may had significant effects(P<0.05)on the microbial communities diversity for certain phyla or class,such as BRC1 and Epsilonproteomicrobial. |
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