| Since Hainan Province fully implemented the work of pond-to-mangrove restoration in 2018,the changes of the mangrove ecosystem came from the original pond area are still unclear.Therefore,this study selected Dongchang Village of Xinying Mangrove Wetland Park in Hainan Province as the experimental sample site.We choose 3 culture pond and 3 natural areas outside ponds to make a comparative research the hydrological factors,sediment factors,vegetation community structure,macrobenthos and the structure of the microbial community,focusing on explaining the impact of human activities such as pond culture and pond-to-mangrove restoration on mangrove sediment biological systems.The main research conclusions of the article are as follows:(1)Through the China’s mangrove forest distribution dataset(2015),After extracting and calculating,it is found that pond culture has caused obvious damage to the vegetation of the mangrove community.Since 1970,the area of mangroves has been significantly reduced.In 2015,the area of mangroves in the pond area decreased by 43.62%compared with 1970.Moreover,as far as the vegetation coverage of the sample plot is concerned,the vegetation coverage of the natural forest outside the pond is 82.50%,which is significantly higher than the vegetation coverage in the pond of 36.80%(p=0.020).There is no significant difference in plant density/plant height/diameter cross-sectional area/base diameter cross-sectional area of the square plants between in culture ponds and natural state,and the leaf length and tip length are also insignificant.Only on the index of leaf width,the pond forest is significantly larger than the natural one(p=0.003).,which is related to the N element content of the sediment in pond culture.(2)Through the research on the water quality parameters and sediment physical and chemical factors of the sample plots,the average salinity of seawater measured this time is 8.85‰,the salinity is low.The temperature,salinity and conductivity of the water in the pond are significantly higher than those outside the pond.The sediment of the sample plot is acidic and low in salinity.After 1.5 years and 2 years from pond-tomangrove restoration,the pH of the sediment generally increases with the increase of sediment depth.The pH range of the sediment in the 1.5-year retreat is 2.77～4.14,the pH range of the sediment in the 2 years retreat is 2.18～4.97;the salinity of the 1.5 year retreat is ranged 2.6～8.0‰,and the salinity of the sediment is ranged 3.4～5.1 ‰.In 1.5 years and 2 years after pond-to-mangrove restoration,the sediment pH generally showed a trend of increasing with the increase of sediment depth.After 2 years from pond-to-mangrove restoration,the salinity of the surface sediment is higher than the salinity of the deep layer,and the salinity of forest land is higher than that of bare land.(3)There were 8 species of benthic animals in the natural forest in 1.5 a,14 species in 2 a;12 species of benthic animals in the pond forest in 1.5 a,and 14 species in 2 a.A total of 25 species of benthic animals were found in the survey,including 10 species of gastropods,4 species of crustaceans,7 species of bivalves,3 species of polychaetes and 1 specie of insect larva.The species diversity index H is ranged from 1.14 to 2.70,and the evenness index J is ranged from 0.56 to 0.86,the Marglef abundance index d is ranged from 0.68 to 1.73,and the ENS effective species index is ranged from 3.54 to 15.44.There was no significant difference in diversity parameters inside/outside the pond after 1.5/2 years from pond-to-mangrove restoration.The dominant benthic species on the plot is Assiminea latericea,which conforms to the characteristics of mangrove habitat.Decrease of C and S content makes it possible for the Neanthes glandicincta to be the dominant species.Through cluster analysis,the distance among natural forests is relatively close,and the distance from pond forests is relatively long.The results of cluster analysis in 2 a show that the distance between bare land and adjacent forested land is closer than the distance between bare land.(4)The 16s DNA results of sediment microbial sequence and diversity analysis show that the number of observed species,Shannon diversity index,and Chaol richness index are all high,showing the high diversity of sediment microbes in this area.The diversity of microbial species in 2 a after pond-to-mangrove restoration is higher than that in 1.5 a,and it shows different microbial community structure characteristics between 1.5 a and 2 a.There are significant differences between natural forests and pond forests in 1.5 a,but no significant differences between the two in 2 a.While in 2 a,there are more significant differences in microbes in the deep and surface layers of the sediment in the forest or bare land.The main microbial phylum in 1.5 a and 2 a are Proteobacteria,Firmicutes,Bacteroidetes,etc.The main phylum of great difference between pond forest and natural forest in 1.5 a is Proteobacteria,Bacteroidetes,Actinobacteria and Fusobacteria.The main phylum of great difference in 2 a is Cyanobacteria,Desulfobacterota,Campilobacterota,Verrucomicrobiota,Asgardarchaeota,Modulibacteria,Nitrospirota,Deferrisomatota,TA06.Comparing the bare land in culture ponds and natural state in 2 a,it was found that there was no significant difference in microbial diversity and abundance in the forest and outside the forest,but the microbial community structure was quite different,and the function annotation results outside the forest showed that its functional groups were not active,nor like the function of microbes inside the forest.Through correlation analysis of microorganisms and environmental factors,high water content and low pH are considerated important reasons for maintaining the high diversity of sediment microorganisms in 2 a.The main bacterial groups related to metabolism are Desulfatiglans,Sulfurimonas,Sulfurovum and Nitrosopelagicus.Desulfatiglans,Sulfurimonas and Sulfurovum are positively correlated with S in 1.5 a.Desulfatiglans,Nitrosopelagicus are not significantly correlated with S,but are positively correlated with C,N and other elements.(5)The content of nutrient elements in the sediments in 2 a after pond-to-mangrove restoration was lower than that of 1.5 years,and the diversity of microbial species and macrobenthic diversity parameters increased.From the perspective of the differences between natural forests and pond forests,the differences in sediment factors,microbial community structure and macrobenthic community structure in 2 a after pond-tomangrove restoration were less than 1.5 a.The status of sediment biological groups in this area is active,and the diversity is increasing,and the sediment conditions are conducive to the restoration of mangrove biodiversity after pond-to-mangrove restoration.However,the destruction of vegetation in the ponds is still serious,and the vegetation has not been significantly restored.It is recommended to promote mangrove coverage by artificial replanting. |
