Ecological Degradation Of Alpine Wetland In The First Meander Of Yellow River And Its Restoration Countermeasures

Wetland is a system of plant,water,soil and other elements organically coupled in the spatial structure.It plays an outstanding role in regulating regional microclimate,conserving water,protecting biodiversity and maintaining ecological balance.In recent years,with the increase of climate change and human activities,wetland area has been sharply reduced,wetland degradation problem is becoming increasingly serious,making wetland ecosystem has become one of the most threatened ecosystems in the world.The alpine wetland the wetland of first meander of Yellow River is the most representative of the alpine inland wetland.Its special geographical location and high-altitude environment exacerbate its vulnerability.Under the dual influence of human activities and climate change,the wetland area decreases,leading to the reduction of water conservation capacity,and it is faced with a severe situation of protection and restoration.Therefore,it is of great theoretical significance and practical value for the protection and restoration of alpine wetland vegetation and soil to study the effects of ecological degradation on plant community characteristics and soil physical and chemical properties in the wetland of first meander of Yellow River and the restoration measures.In this paper,the wetland of first meander of Yellow River National Nature Reserve in Gansu Province was taken as the research object,and Landsat remote sensing images of 1990,2001,2009 and 2020 were obtained based on Google Earth Engine(GEE).And calculated the Normalized Differnce Vegetation Index(NDVI)and Soil Moisture Monitoring index(SMMI).The spatial and temporal changes of wetland ecological degradation were analyzed by two-dimensional judgment matrix and the spatial distribution map of wetland ecological degradation was determined.On this basis,82 survey sites were set up in combination with traffic accessibility and uniformity,and the plant survey,soil sample collection and physicochemical property analysis of various sites were completed.The methods of variance analysis,Principal component analysis(PCA)and Redundancy analysis(RDA)were used to calculate the plant community characteristics(species diversity index,phylogenetic index and ecological niche).The characteristics of wetland plant community and physicochemical properties of wetland soil under different degradation levels were analyzed.The effects of wetland ecological degradation on plant community and soil characteristics and the relationship between wetland plant community and soil factors under different degradation levels were revealed.Finally,the restoration measures of alpine wetland ecological degradation in the wetland of first meander of Yellow River are put forward.The research conclusions are as follows:(1)The vegetation status of the alpine wetland of first meander of Yellow River is good,and the vegetation coverage is high,showing a spatial distribution pattern of high around and low in the middle.The spatial heterogeneity of soil moisture was significant,and the low-value moist areas were concentrated in the low-lying areas in the central and southern part of the reserve and the valley gathering areas in the southeast.From2009 to 2020,the area of slight ecological degradation type of alpine wetland was1040.58 km~2,with the largest proportion.In terms of spatial distribution pattern,the spatial distribution of non-degraded types was closely related to vegetation and soil moisture.The mild and moderate degradation types were mainly distributed in the west and northeast of horse ranch at first meander of Yellow River,southwest of Manrima,north and northwest of Caima,and north of Qihama.The severe degeneration types were concentrated in the desertified areas of the protected areas.(2)The ecological degradation of alpine wetland in the wetland of first meander of Yellow River has a significant impact on plant community characteristics.With the increase of wetland degradation,plant coverage,density and aboveground biomass decreased significantly(P<0.05).The diversity index showed a single-peak growth pattern,and the plant community structure tended to be complex first and then simple.The species niche width,community phylogenetic diversity and phylogenetic structure index of gramineous plants(especially Poa annua,Elymus nutans,etc.)decreased with the increase of wetland degradation degree.Most of the more distant related species coexisted in the community,and the phylogenetic pattern of the plant community changed from aggregation to dispersion.(3)The degradation of wetland is not conducive to the accumulation of soil nutrients and enhances the alkaline trend of soil.With the increase of wetland degradation,soil organic carbon and total nitrogen decreased significantly,while the ratio of carbon to nitrogen and p H value increased significantly(P<0.05).Soil factors affecting plant communities were different under different wetland degradation levels.In severely degraded wetlands,soil is weakly alkaline,and p H is negatively correlated with plant diversity,which is not conducive to plant growth.In moderate,mild and non-degraded wetlands,soil is neutral,and p H is positively correlated with plant diversity.In mildly and moderately degraded wetlands,organic carbon was positively correlated with plant diversity and phylogenetic structure index,which may be due to the residual effect of moderate interference on the relationship between nutrients and plants.(4)In non-degraded wetlands,vegetation and soil are in good condition,so wetland ecological environment monitoring should be strengthened,and intervention can be carried out by eliminating noxious weeds when necessary.In mildly degraded and moderately degraded wetlands,the grazing ban and rest period should be reasonably planned to avoid unreasonable human interference activities,and vegetation restoration should be carried out through supplementary planting of dominant local Poa annua or mixed sowing of Elymus nutans or Legume,and soil fertility should be improved.In severely degraded wetlands,desertification control should be given top priority,and the mode of"grass grid+soil covering+fertilization+supplementary seeding"should be adopted.