Effects Of Different Reclamation Methods On Macrobenthos In Nanhui And Chongming Dongtan Wetlands

Wetland reclamation is a common ecological project,such as the treatment of Spartina alterniflora through reclamation for water storage.However,the fully enclosed reclamation method has a greater impact on the wetland ecosystem.Currently,semi-closed reclamation and opened reclamation are commonly used,but it is necessary to carry out relevant research on whether these methods will also have a certain impact on wetland organisms.This thesis studied the community structure and the ecological quality of macrobenthos in Nanhui wetland and Chongming Dongtan wetland under different reclamation habitats.The effects of different reclamation methods on macrobenthic community and environmental factors in the two regions were compared.At the same time,the change trend of macrobenthic community structure after reclamation was discussed combined with the historical data.This thesis aims to provide basic data and theoretical support for the improvement and optimization of the Yangtze Estuary wetland habitat environment and the ecological protection and artificial restoration of wetland resources.The results of the study are as follows:1 Comparative study on macrobenthos in different habitats in reclaimed wetland of Nanhui DongtanThe macrobenthos in Nanhui Dongtan reclamation wetland was sampled and investigated in the spring and autumn of 2018 and 2019.According to different reclamation areas,transect S1 was set up in the fully enclosed reclamation area;transect S2 and S3 were set up in the opened reclamation area.Each reclamation area was divided into two habitats,bare tidal areas and vegetated regions,named SG1-SG3 and SC1-SC3 respectively.The results showed that a total of 37 species of macrobenthos from 25 families,7 classes,5 phyla were collected in the two-year ecological survey of Nanhui Dongtan wetland.Compared with the opened reclamation area,the number of species,density,biomass and species richness in the ful y enclosed reclamation area decreased,while the number of dominant species and species evenness increased relatively.The common dominant species in fully enclosed reclamation areas were small and medium-sized benthic animals such as Notomastus latericeus,stenothyra glabra,and Corbicula fluminea,while the dominant species in opened reclamation areas were mainly Corophium sinensis and Ilyoplax deschampsi.There were no significant differences in species number,species diversity index(H'),taxonomic diversity and functional redundancy between bare tidal areas and vegetated regions.The density and biomass of macrobenthos in SG1 and SC1 were significantly decreased(P<0.05).The species richness index(d)of SG1 in bare area was significantly decreased(P<0.05),and the species evenness index(J'),functional diversity index(FD_Q)and functional dispersion index(FD_is)of SG2 in bare tidal areas were also significantly decreased(P<0.05).The results of clustering and NMDS showed that the composition of macrobenthos in the ful y enclosed reclamation area and the opened reclamation area were significantly different,and the clustering distance between bare tidal areas and vegetated regions in the opened reclamation area was farther.These results indicated that compared with the ful y enclosed reclamation area,the species composition in the opened reclamation area had little change,and the benthic organisms were more abundant.Compared with bare tidal areas,macrobenthos in vegetated regions have higher and more uniform classification,better community diversity,and more stable and functional communities.The evaluation of habitat quality of Nanhui Dongtan wetland showed that the macrobenthos in ful y enclosed reclamation area were mainly G_I,which is dominated by species sensitive to environmental disturbance,and G_III,which is dominated by species tolerant to environmental disturbance.The benthic community in the reclamation area was dominated by G_III.Combining the results of various macrobenthos index,it was found that the macrobenthic community in SG1 was disturbed,and the ecological quality was in moderate level;The environmental quality of SC1 is good,and its community is slightly disturbed;The ecological quality of SG2 was in good or moderate level,while the disturbance degree of SC2,SG3 and SC3 was low,and the ecological quality was above good.The above results show that the macrobenthic community in the bare tidal area was more susceptible to mild or moderate disturbance both in the fully enclosed reclamation area and the opened reclamation bare tidal area and their ability to resist the risk of environmental disturbance decreases,and the ecological environment quality in bare tidal areas were in good or moderate level.2 Comparative study on macrobenthos in different habitats after ecological optimization in Chongming Dongtan wetlandA field sampling survey was conducted on macrobenthos in the Chongming Dongtan wetland from May 2019 to November 2021.There are two kinds of habitats in Chongming Dongtan wetland:semi-closed reclamation area and natural tidal flat area(including the original natural tidal flat that has not been implemented,and some natural tidal flats that have been retained after the implementation of the project).Sampling points C1,C1A,C2,C2E and C3 were set in the semi-closed reclamation area,and the original tidal flat S1 and the reserved tidal flat S2-S4 were set in the natural intertidal zone.In three years,a total of 80 species of macrobenthos were collected from 9 phyla,11 classes and 58 families in Chongming Dontan wetland.The number of species in the semi-closed reclamation area had no significant difference from that of the original tidal flat and the reserved tidal flat,but the number of dominant species in the semi-closed reclamation area(12 species)are less than that in the natural tidal flat(19 species).The common dominant species in the semi-closed reclamation area were Stenothyra glabra,Assiminea sp.,and Chironomid larva,while dominant species such as Notomastus latericeus,Assiminea latericea,Stenothyra glabra,Corophium volutator and Ilyoplax deschampsi were widely distributed in the tidal flats.The density of macrobenthos in the semi-closed reclamation area was significantly lower than that of the reserved tidal flat(P<0.05),and its biomass was significantly lower than that of the natural tidal flat(P<0.05).The biodiversity of C2 was the lowest,and the biodiversity of other semi-closed reclamation areas was similar to that of natural tidal flats.The results of clustering and NMDS showed that the community composition of macrobenthos in the semi-closed reclamation area was similar,and the clustering distance was closer to that of the original tidal flat.The above results showed that the ecological optimization project had improved the habitat environment of the semi-closed reclamation area,and the community structure and ecological function of macrobenthos in semi-closed reclamation area was similar to that in natural tidal flat.The evaluation results of the habitat quality showed that the macrobenthos ecological community in the semi-closed reclamation area and the natural tidal flat were mainly G_I,G_?and G_?.C1,C1A and C3 possessed better habitats in the semi-closed reclamation area,and their macrobenthic communities were less affected by the disturbance of the ecological optimization project.The macrobenthic community in C2was moderately or heavily polluted,and the community in C2E was slightly or moderately polluted.S1 in original tidal flat was less disturbed and the habitat quality was good;the habitats of the reserved tidal flats S2 and S3 were disturbed,and the ecological environment quality of S4 was good or even in moderate level.The above results showed that the pressure of the ecological optimization project and human activities still exists,which had a certain negative impact on the ecological quality of some semi-closed reclamation areas and remaining wetlands,and the benthic community structure was disturbed.3 Macrobenthic community in different reclaimed habitats and their relationship with environmental factorsFrom May to December 2019,the environmental correlation of macrobenthic community in different reclamation areas and tidal flats in Nanhui and Chongming Dongtan wetlands was investigated.The results showed that the dominant species of macrobenthos in the five habitats were preserved tidal flat(6 species)>fully enclosed/semi-closed reclamation area(4 species)>original tidal flat(3 species)>opened reclamation area(2 species).The average density of macrobenthos in the fully enclosed/semi-closed reclamation area and the original tidal flat area decreased significantly(P<0.05),and the average biomass in the fully enclosed/opened reclamation area was significantly lower(P<0.05).The biodiversity of the five habitats was about the same.However,the species distribution evenness in the preserved tidal flats decreased significantly(P<0.05),and the functional diversity index(FD_Q)of the ful y enclosed/opened reclamation area was significantly lower than that of the original tidal flat(P<0.05).Different reclamation areas and tidal flats had obvious differences in water salinity and in sediment content in below-median particle size.The density and biomass of macrobenthos were closely related to the changes of environmental factors including dissolved oxygen,p H,salinity,and sediment content,while species uniformity,functional diversity and functional redundancy were mainly affected by sediments in different particle sizes.Different dominant species were also affected by changes in environmental factors.The results showed that salinity decline,sediment changes,and habitat heterogeneity caused by reclamation activities were the main reasons for the differences in the succession of macrobenthos in different reclamation areas and tidal flats.Combining the historical data with the 2019 survey results,it can be found that the interannual changes in species numbers,average densities,and species diversity in the five study areas showed an overall upward trend.The species composition had changed significantly.The dominant species in the three reclamation areas and the reserved tidal flats tended to be miniaturized.The average biomass of the fully enclosed reclamation area had little inter-annual change,while the average biomass of the opened reclamation area increased first and then decreased.The results showed that there was a succession trend—small individual species replacing large species in the three reclaimed areas and reserved tidal flat.The high habitat heterogeneity was conducive to the recovery of macrobenthic community after reclamation.It is suggested to strengthen the dynamic monitoring of biological resources in the wetland reclamation area through scientific planning of reclamation projects.Taking measures such as choosing semi-closed/opened reclamation methods,planting indigenous plants,and placing highly adaptable species can promote the restoration and healthy development of the ecological environment in the Yangtze river estuary wetlands.