Effects Of Hydrological Changes On Soil Physical Characteristics And Vegetation Community In Xidahu Wetlands Of Heihe River

Heihe Wetland National Nature Reserve is a typical inland desert wetland ecosystem.It is also an important ecological security barrier in Northwest China and a water conservation area in the lower reaches of Heihe River.Under the background of climate change and the general threat to wetland ecological security,the hydrological,soil and vegetation conditions of marsh wetlands in Heihe Reserve have changed accordingly.For this reason,a typical herbaceous marsh wetland in the reserve was selected as the research object.Fixed sample plots were set up in the wetland to carry out field investigation and monitoring of wetland hydrology,soil and vegetation for three consecutive years.Through correlation analysis,the temporal and spatial distribution of groundwater depth and soil moisture in herbaceous marsh wetlands in protected areas was clarified,the effects of groundwater depth change on soil physical properties and vegetation communities were discussed.The coupling relationship between "hydrological change-soil physical characteristics-vegetation community" is attempted to explain.The countermeasures and suggestions for wetland protection and restoration are put forward,which can provide reference for rational exploitation of wetland water resources.It is of great scientific significance for the sustainable development of wetland ecological environment.The main results are as follows.:(1)Spatial and temporal variations of hydrological elements in wetlandsThe spatial variation of groundwater depth in different regions of wetland is large,showing deep summer and autumn,shallow winter and spring.The annual average value is 2016(42.28 cm)>2017(38.88 cm)>2015(34.33 cm);the annual average value of soil moisture is 2015(46.79%)>2016(45.36%)>2017(43.10%).The annual variation is not significant(P>0.05),but there is a downward trend;The soil depth of 0-20 cm,the correlation degree between soil water content and groundwater depth is the highest.(2)Response of Soil Physical Characteristics to Groundwater Burial DepthWith the deepening of groundwater burial,the content of soil silt decreases(P<0.01),sand increases(P<0.01),and clay changes slightly.Soil texture types in shallow,middle and deep areas are silty clay loam,clay loam and sandy clay loam respectively,and soil texture gradually increases.Soil bulk density gradually increases with the deepening of groundwater burial,and porosity and water holding capacity both increase with the depth of groundwater.The depth of groundwater decreased with the increase of groundwater depth,and there was a significant correlation between most soil physical factors(P<0.05).(3)Response of vegetation communities to changes in groundwater depthIn the past three years,29 species were found in the sample plots,among which Gramineae was the dominant family of wetland plants and Phragmites australis was the dominant species.With the increase of groundwater depth,mesophytes and xerophytes gradually replaced wet plants as dominant species,and species richness and diversity were the highest in the median area of groundwater depth.The aboveground and belowground biomass decreased with the increase of water depth,while the root-shoot ratio increased gradually.(4)Coupling mechanism between environmental factors and vegetation communitiesThere are differences in environmental factors affecting plant community indices under different water burial depth gradients.Shallow water burial depth area is water holding capacity,soil bulk density,sand,silt;medium water burial depth area is soil bulk density,sand,silt;deep water burial depth area is capillary porosity,total porosity,clay,sand;overall situation is total porosity,silt,groundwater burial depth,soil bulk density.