Distribution And Ecological Effects Of Heavy Metals In Mangrove Sediments In South China Under The Influence Of Human Activities

In order to study how human activities influence the distribution and ecological effects of heavy metals in mangrove sediments in South China,the surface sediments and core sediments of mangroves in Guangdong-Guangxi region were sampled.Our goals were to explore the spatial variability and the ecological risk of heavy metals with surface sediments,and then analyzed the source of heavy metals by measuring the occurrence of core sediments.Firstly,this study analyzed the heavy metal content of surface sediments and the corresponding heavy metal content of the new leaves of plant canopy,and evaluated the pollution of heavy metals in surface sediments with pollution load index method,and evaluated the enrichment coefficient of heavy metals in plant canopy new leaves.We also measured the physical and chemical properties of surface sediments,organic matter,and organic matter of plant canopy new leaves.Combined correlation analysis and multivariate analysis of variance were used to explore the spatial variability and migration characteristics of surface sediments by natural and human factors.Secondly,this study analyzed the total amount of heavy metals in core sediments,evaluated the potential ecological hazard index of heavy metals in core sediments,and simultaneously measured the physical and chemical properties and organic matter of core sediments,and combined correlation analysis to explore the correlation of physical and chemical properties and organic matter and heavy metals in core sediments,then explored the vertical distribution of heavy metals(Cr,Ni,Cu,Zn,Pb),vertical distribution of physical parameters such as particle size,water content,p H,oxidation-reduction potential(Eh)and organic matter(total carbon,total nitrogen),combined with deposition rate,summarized the trend of heavy metal pollution with age,and explored the influence of human activities.Finally,we analyzed the occurrence of heavy metals in core sediments.The ratio of secondary and primary phases was used to evaluate the source and ecological hazard of heavy metal pollution.The main results of this study are as follows:1.The average level of heavy metals in the surface sediments of Futian mangroves in Guangdong was the highest,and the regional pollution load index was the highest,1.37,which was moderately polluted.The following are the Dangjiang mangroves in Guangxi,Gaoqiao mangroves in Guangdong,Shankou East mangroves in Guangxi,Shankou West mangroves in Guangxi,and the Binhai mangroves in Guangxi with the lowest average level,all of which were non-polluting.The particle size distribution of the six sites is dominated by silt and the p H is acidic.The average level of organic matter in the surface sediments of Futian mangroves in Guangdong was the highest,and the average level of organic matter in the surface sediments of Binhai mangroves in Guangxi was the lowest.2.Through correlation analysis and multivariate analysis of variance,it was found that TC,TN and salinity were significantly correlated with the distribution of heavy metals in the surface sediments.Vegetation types also had a significant effect on the distribution of heavy metals in surface sediments.Different mangrove plants had different adsorption capacities for different heavy metals.Bruguiera gymnorrhiza and Rhizophora stylosa were highly tolerant to Zn;Avicennia marina had strong adsorption capacity for zinc,lead,copper,nickel and chromium,but the accumulation of heavy metals may be lower than Kandelia obovata and Sonneratia apetala.The results also found that the sampling location had a significant impact on the distribution of heavy metals in surface sediments.Different sampling locations had different levels of economic development and population,also the main industries and the degree of human activities were different.3.The average content of heavy metals Cr,Ni,Cu,Zn and Pb in the core sediments of Hong Kong mangroves were the highest,followed by Futian mangroves in Guangdong,and the average levels of five heavy metals in Shankou mangroves in Guangxi were the lowest.The comprehensive potential ecological hazard coefficients of the three mangrove core sediments were 40.83,32.67,and 8.71,which were all minor potential ecological hazards.The particle size distributions of the three sites were similar,mainly silt,the p H of Hongkong Mipu mangroves was weakly alkaline,and the p H of Guangdong Futian and Guangxi Shankou mangroves were strongly acidic.The average content of organic matter in the core sediments of Shankou mangroves in Guangxi was the highest.4.There were certain regularities in the vertical distribution of heavy metals and the vertical distribution of physical and chemical properties in the Futian mangroves in Guangdong,the Shankou mangroves in Guangxi,and the Mipu mangroves in Hongkong.The heavy metals in the core sediments of the Mipu mangroves in Hongkong,except for Pb,decreased with the increase of depth;the overall heavy metals of the core sediments of Futian mangroves in Guangdong were not obvious with depth and were relatively stable;The heavy metals in the core sediments of Shankou mangroves in Guangxi decreased with the increase of depth,and Cr and Ni increased abnormally at the bottom of sediments.5.For heavy metal Cr,the residual was the predominant form.The Ni elements in the three locations were mainly in the form of residual.This indicated that Cr and Ni were mainly natural sources.For heavy metal Cu,the ratio of the occurrence of morphological value in the Futian mangroves in Guangdong and the Mipu mangroves in Hongkong were the largest in the reductive,and the ratio of the oxidizable were the smallest,indicating that there may be an artificial source;while in the Shankou mangroves in Guangxi,the ratio of the storage form was the largest in the residual,and the ratio of the acid extractable was the smallest.The ratio of Zn occurrence in Guangdong Futian and Hongkong Mipu mangroves were the largest ratio of acid extractable,which may be caused by human activities.However,the ratio of occurrence of Zn in the Shankou mangroves in Guangxi from the residual was the largest in surface to the acid extractable state was the largest in bottom.For the heavy metal Pb,the Pb elements in the three locations were mainly in the reducible state,and the human activities were obviously affected.It shows that Pb could be re-released under certain conditions and had ecological risk that cannot be ignored.6.Among the three locations,Guangdong Futian and Hongkong Mapu mangroves were close to each other because of their geographical location.Therefore,the vertical distribution of the heavy metals in the two locations was similar,and the ratios of the various forms were similar.Both Zn and Pb were heavily polluted.Cu in Futian mangroves in Guangdong was moderately polluted,and Cu in Mipu mangroves in Hongkong was heavily polluted.The vertical distribution of the occurrence of heavy metals in the Shankou mangroves in Guangxi and the other two locations was slightly different,and the ratios of the various forms were quite different.Only Zn was slightly polluted,and Pb was heavily polluted.Different heavy metals may change in different places,and the order of occurrence ratio may change.The form of the main body may also change.Except for the residual state,the other three forms had the risk of being released into the environment under certain conditions.