Study On The Distribution Of Diatoms And Their Correlation With Environmental Factors In Sediments Of Wetlands In The Sanjiang Plain

Wetland is one of the most biodiverse ecosystems on the planet and has a series of ecological functions such as regulating the flow,improving water quality and protecting biodiversity.Sanjiang Plain is the largest concentrated freshwater wetland in China.Understanding its long-term paleoenvironmental evolution process is conducive to a better comparative analysis of the changing rules of wetland ecosystems under the influence of different driving forces,so as to provide important basis for forecasts of future environmental changes.The original deposition process of the wetland records the paleoenvironmental information.Diatoms,as a kind of micro-organisms with siliceous shells and living in water or moist environment,are preserved in sediments,and fossil diatom assemblages can be used to infer the paleoenvironment and paleoclimate of wetland.At present,the paleoenvironmental qualitative and quantitative studies of diatoms as the biological proxy indicators of environment are rarely reported in the northeastern China,especially the Sanjiang Plain wetland,and the understanding of the significance of the diatom hydro-environmental indication in this area is still insufficient.In this paper,field sampling and reasonable mathematical statistics methods were used to identify the composition and distribution of diatom assemblages in surface sediments and peat cores of wetland in Sanjiang Plain,and to study the relationship between diatom composition distribution and water environment factors in surface sediments.After defining the key environmental factors that affect diatom species composition most,diatom-environmental transfer function relationships were established.And qualitatively analyzing and quantitatively reconstruction of paleoenvironment based on sediment peat core dating techniques were proceeded to obtain its evolution sequence that provides an important data foundation for the restoration of wetland environment in the Sanjiang Plain.The research on diatom-based wetland will help us understand the environmental and climate changes of the Sanjiang Plain as a high-latitude and climate-sensitive region,and further understand the formation and development of the Holocene water level and peatland.It also provides basic data for the study of diatoms in the sediments of wetlands in Sanjiang Plain.This main conclusions are as the follows:（1）Diatom species of peatlands in the Sanjiang Plain are rich in resources.In this study,141 species and subspecies of 19 genera of modern surface sediment diatoms were identified;158 species and subspecies of 19 genera of diatoms were identified in paet core.In terms of abundance values,the dominant species in surface sediments include H.amphioxys,G.lagerheimii,C.paucistriata,and N.ignota Krasske var.ignota,etc.;the dominant species in the sedimentary core are A.crenulata,N.cuspidata and N.perminuta et al.（2）Water level（WL）is the most important environmental factor that affects the species composition of diatoms.Through multivariate unconstrained and constrained ordination analysis,the water level alone explained 7%of the species variability information,which was higher than the interpretation of species variation by other environmental variables and reached a significant level by the Monte-carlo（499）permutation test（p<0.05）.（3）Applying the response law of diatom species to environmental changes,the characteristics of the Holocene water level changes of Honghe peat core were qualitatively described and analyzed.The key species that prefer the deep water（A.crenulata,N.cuspidata and P.brevicostata）and shallow water（N.perminuta and E.bilunaris var.mucophila）strongly suggest wet and dry conditions of the Sanjiang Plain in the Holocene at different time scales.The main dominant species,A.crenulata,decreased with depth,and N.perminuta,preferring to inhabit peat moss swamps,showed the opposite trend,indicating that as the depth decreased,the water level gradually decreased from the Holocene to the present.The Honghe peatlands overall showed a tendency to dry.（4）Diatom-water level transfer function relationship in paetlands of Sanjiang Plain were constructed.The weighted average least squares（WAPLS）has the best performance through the comparison of different transfer function models such as WA,PLS and WAPLS.The model shows a high coefficient of prediction(R²_jack=0.2201)and a low predictive error(RMSEP_jack=0.2339).（5）A preliminary attempt was made to use diatoms for the quantitative reconstruction of history water levels in the Sanjiang Plain.The constructed diatom-water level transfer function was applied to peat core fossil diatom data to reconstruct water level changes in the study area for nearly 6.5 ka.On the whole,the wetland environment in the Sanjiang Plain has gradually become dry,and has fluctuate more violently in recent centuries.