| Salt marsh is a saline or brackish water muddy tidal flat covered with vegetation,which is periodically or intermittently affected by ocean tides.The benthic macroinvertebrates serve as the animal fauna in all or most of the time in salt marsh sediments.The benthic macroinvertebrates play an important role in the material transport and energy transfer of the food chain,and they are essential to maintaining the function and structure of the regional ecosystem.The variation of erosion and deposition of sediment is the basic physical processes of salt marshes in the estuarine coast.It is an important factor affecting the composition and distribution of macrobenthic communities.From the perspective of functional groups,studying the impact of the variation of erosion and deposition of sediment on macrobenthic fauna and their ecological functions can simplify the analysis of the internal structure of the community and better reflect the characteristics of habitats and the functions of macrobenthos in ecosystems.In this study,Shanghai Nanhui Dongtan Salt Marsh was selected as the study area.A fixed sampling site was set up to establish research methods and specific experimental schemes.The experiment was divided into two parts.In the first part of the experiment,quarterly collection and analysis of macrobenthos and sediment samples were conducted,and macroinvertebrates were divided into functional groups according to their feeding habits.Based on this,the effects of erosion and deposition changes in salt marshes on macrobenthos functional groups were studied.In the second part of the experiment,macroinvertebrates and sediments were collected and analyzed in the three quarters of the growing season,to study the effects of erosion and deposition changes in salt marsh wetlands on the ecological functions of macrobenthos on heavy metals.The main research results can be summarized as follows:1)The variation characteristics of erosion and deposition and other environmental factors of sediment in salt marshIn the first year of investigation,the Nanhui Dongtan surveyed area overall showed a state of slow deposition.The variation of erosion and deposition of sediment showed a significant temporal change(P<0.01).Overall,in the entire survey area,deposition was relatively fast during the flood season,and deposition was relatively slow during the dry season.In terms of spatial variation characteristics,the variation of erosion and deposition of sediment also showed extremely significant changes among the entire plots(P<0.01).In the second year of investigation,the characteristics of erosion and deposition of sediment have changed due to the changes in the study area.In the first quarter,the surface sediments was flushed overall,while deposited in the second quarter.There were extremely significant differences between two quaters(P<0.01).From section 1 to section 4,the surface sediment evolved from erosion to deposition.The temperature of sediments,salinity in pore water,pH and ORP all showed very significant temporal changes(P<0.01).Except temperature,there were significant spatial changes in salinity,pH,and ORP(P<0.05).There were significant temporal and spatial changes in the median grain size,total carbon content,and total nitrogen content of sediments at different depths(P<0.01).2)Correspondence between erosion and deposition changes and other environmental factors and benthic macroinvertebrate functional groupsA total of 49 species of macrobenthos were collected during the survey.The dominant species were Stenothyra glabra and Potamocorbula amurensis.According to feeding habits,the functional groups of macrobenthic communities were divided into three groups: mainly omnivores,35 species,9 herbivores,and 5 carnivores.There were significant correlations between the variation of erosion and deposition of sediment and other environmental factors and species,density,and biomass of macrobenthic communities and functional groups(P<0.05).The correlations between the same environmental factor and the number of species,density,and biomass of different macrozoobenthic communities or functional groups may be different.There were significant negative correlations between the variation of erosion and deposition of sediment and the variationof the species number and density of the macrozoobenthic communities and the species number and density of omnivore(P<0.01).In addition to the direct impact on the benthic macroinvertebrate,the variation of erosion and deposition also indirectly affected macrobenthos by changing the characteristics of sedimentary physical-chemical factors.Although the number of species of three feeding functional groups decreased,the nutrient environment in the sediments was more conducive to the survival of omnivores than the other two functional groups.Over time,omnivores' strength in density and biomass will gradually emerge.3)Corresponding relationship between sediment erosion and deposition changes and other environmental factors and heavy metal contents in benthic macroinvertebrateIn the study,the dominant species widely selected in each season were collected.In April and October of 2017,the dominant species of Potamocorbula amurensis was selected for bivalves,and the dominant species of Corbicula fluminea was selected for gastropods in July of 2007.For macrobenthos,the effect of the variation of erosion and deposition of sediment and other environmental factors on the species of individuals varies.Sediment erosion and deposition variation and other environmental factors had different effects on the heavy metal content in different species.Sediment erosion and deposition variation affected the contents of Cu,Zn,and Cr in the bivalves,and the content of Cu and Zn in the gastropods.There were significant positive correlations between the sediment erosion and deposition variation of sediment and the absorption of Cu,Zn and Cr by bivalves and the absorption of Cu and Zn by gastropods,indicating that sedimentation were related to theincreaseof absorption of heavy metal elements by macrobenthos.Sediment erosion and deposition variation plays a leading role in the change of physical indicators of sedimentation.In addition to the direct effects on the ecological functions of macrobenthos,it also indirectly affects the ecological functions of macrobenthos by changing the characteristics of sedimentary physical-chemical factors.There were positive correlations between the median grain size of sediments and the heavy metal content of macrobenthos.That is,as the median size of sediments increases,it will promote the absorption and enrichment of heavy metals by macrobenthos.The total carbon content and total nitrogen content in sediments also had certain correlations with heavy metal content in macrobenthos.However,differences in species and heavy metal elements make the correlation with nutrients also have some differences.In the future,based on multi-factor system monitoring,relevant research needs to conduct comprehensive and systematic long-term analysis of the effects of erosion and deposition changes in salt marsh wetland on macrobenthos. |
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