| The floodplain wetland is a precious natural resource for mankind,has the function of regulating regional ecology and environment,and provides irreplaceable direct or indirect services for mankind.In recent years,due to the combined impact of global climate change and human disturbance,the ecological environment of floodplain wetlands has been severely disturbed and destroyed.The problem of wetland degradation has become a major challenge for the sustainable development of the ecological environment.In this study,the floodplain wetland in the lower reaches of the Hailaer River was used as a typical research area,and the method of combining ground monitoring and remote sensing monitoring was used to study the evolution of the forest and grass resources in the floodplain wetland of the Haila River in the past 30 years.It reveals the influence of floodplain wetland inundation status change on vegetation change,and clarifies the correlation between"climate-inundation status-vegetation change".The main findings are as follows:(1)Aiming at the unclear impact of climate change in the study area on river runoff,the association mechanism of"climate-runoff"is proposed.Establish the MK mutation test model,and calculate the characteristics of the four seasons,interannual temperature,rainfall changes and interannual runoff changes in the study area.The results showed that:the annual temperature and rainfall in the study area decreased;the annual runoff decreased;the climate-runoff has a driving correlation mechanism,and the annual average temperature decreased,which led to the increase of the ice cover time in the Hailar River area,suppressed the generation of spring runoff,and decreased annual rainfall.Leading to delays in summer and autumn runoff,affecting the water supply of the river to the wetland of the floodplain.(2)In view of the complex terrain conditions and diverse water body forms in the floodplain wetland development area,the existing water body extraction algorithm solves the problem of low extraction accuracy of complex water bodies.This study is based on 6 water body indexes and combined with the Otsu algorithm(OTSU algorithm)to extract water bodies in complex water bodies.Research to achieve high-precision extraction and identification of water bodies in the floodplain area.The conclusion shows that the six water body indexes combined with the OTSU algorithm have different capabilities in identifying the performance of different target water bodies,the overall accuracy of water body extraction is between 86.12%and 97.85%.The MNDWI water body index has the best comprehensive effect on water body extraction,and the accuracy is high and easy to calculate.(3)In view of the problem that the inundation status of floodplain wetland is generally obtained by interpretation of remote sensing images,but the research results of the inundation status extracted from remote sensing images are not statistically significant,the concept and calculation model of the inundation guarantee rate WIGR(Water Inundate Guarantee Rate)are proposed to further improve the spectral index and hydrology The relationship between the data is calculated to obtain different submerged areas of WIGR,and the factors affecting the submerged state are analyzed and discussed.The results show that the total area of the area with different inundation guarantee rates before and after the runoff abrupt change is that the total area covered by WIGR before the runoff abrupt change is 158.42km~2,and the total area covered by WIGR after the runoff abrupt change is 171.37km~2;rainfall regulates the runoff of the river and affects the river’s performance.The wetland water supply of the floodplain affects the guarantee rate of river inundation;the WIGR increases as the distance from the river bank is closer;the interaction of human development activities with the surrounding ecosystems has a profound impact on the development and changes of the floodplain wetland.(4)Aiming at the problem of abundant vegetation types and frequent transformations in floodplain wetlands,a vegetation digital change detection model was proposed and developed to realize the spatiotemporal monitoring of vegetation changes in floodplain wetlands.The results show that between 1987 and 2019,the bare soil area of wetland:an increase of 1.08km~2,the area of grassland:a decrease of 13.17km~2,and the area of woodland:an increase of 15.91km~2;the ecosystems in the study area are more dependent on the Hailar River’s runoff replenishment and periodic flood replenishment There are two possibilities for vegetation change trends,positive and negative.In areas with sufficient water supply,the herbaceous plant community gradually changes to the shrubland plant community;in areas with insufficient water supply,the ecosystem changes reversely,and the vegetation changes to bare soil.(5)Aiming at the problem of the unclear influence of floodplain wetland inundation status on vegetation under the background of climate change,the correlation relationship of"climate-inundation status-vegetation change"is proposed,and the spatial distribution and changes of vegetation NDVI in areas covered by WIGR with different frequencies are discussed.The results show that there are regularities in the NDVI values of different WIGR coverage areas,the NDVI value of the high(61-80%)WIGR coverage area is higher than that of the very low(0-20%)WIGR coverage area,and the vegetation in the high(61-80%)WIGR coverage area is well developed,and the vegetation coverage in this area Types are different from very low(0-20%)WIGR coverage areas;high(61-80%),medium(41-60%),low(21-40%),and very low(0-20%)WIGR coverage areas.The impact on vegetation is different.The forest and grassland in low(21-40%)and very low(0-20%)WIGR coverage areas have obvious changes with each other,and the vegetation changes in high WIGR coverage areas are stable;There is a correlation between climate-submerged state-vegetation change.Climate change has an impact on runoff,which makes the natural runoff of the river stabilized,and the number of river water exits decreases.Different submergence guarantee rates will be affected.As the submergence guarantee rate changes,Changes between affected vegetation types.To sum up,the results of this study reveal the temporal and spatial dynamic distribution of the floodplain wetland vegetation(woodland,grassland)in the lower reaches of the Hailar River in the past 30 years,and quantitatively analyze the impact of the inundation state on the vegetation in the region,and clarify the"climate-Submerged state-vegetation change".The above research results provide references for the management,protection and restoration of wetland resources in Hailar area. |
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