Study On Spatio-temporal Variation And Driving Forces Of The County Wetland In Desert Oasis Region

Dengkou County is located in the arid and semi-arid areas of the Hetao Plain and the Wulan cloth and the desert.The strong winds are frequent and the wind erosion is severe and the evaporation is huge.The land desertification is serious and the ecological environment is fragile.The study area has more than 160 large and small lakes,is a veritable "village of hundred lakes",rich wetland resources to protect Dengkou ecological environment,to maintain a stable balance of ecosystems to prevent further deterioration of land desertification and other aspects of a huge role.Efficient and accurate reconstruction of wetland resources information,analysis of its spatial and temporal dynamic changes,for the study area of wetland resources protection and development,ecological civilization construction to accelerate the sustainable development of the economy has guiding significance.Based on the wetland classification system of arid and semi-arid area and the actual situation of Dengkou County,the wetland resources of Dengkou County in the study area are divided into four types:river wetland,lake wetland,swamp wetland and artificial wetland.The Landsat series of remote sensing images covering the study area in 1987,1995,2007,2011 and 2016 were used as the main research data.With the support of 3S technology,the spatial distribution of wetland information in the study area was studied by using object-oriented classification method This paper analyzes the temporal and spatial variation process of Dengkou County wetland from four aspects:area change,spatial change,centroid transfer and landscape pattern change.Finally,the quantitative analysis of its driving force is carried out by using principal component analysis method.,The main conclusions are as follows:(1)Using the object-oriented classification method,the rapid extraction of wetland information in the study area is realized by multi-scale,multi-level segmentation,feature extraction and decision tree establishment.The evaluation accuracy of the six-stage wetland extraction is 91.2%,90.5%,89.4%,92.6%,93.1%and 92.3%respectively.The extraction method is suitable for large-scale wetland research.The decision tree model comprehensively utilizes the characteristics of the brightness,shape index,relative spatial position,NDVI,MNDWI and so on.(2)The wetland of the study area is dominated by natural wetland,and the natural wetland is dominated by lake wetland.The wetlands of the study area are mainly distributed in the southeastern part of the county,and the lake wetlands and marsh wetlands are mainly distributed in the Shajingxu.Artificial wetlands continue to increase,from east to west,from south to north through the oasis.The wetland area of the study area increased in the past 30 years.The total area of wetlands in 1987 was 9467.73ha,compared with 1987,the wetland area increased by 7981ha by 2016,an increase of 84.3%.In the wetland,the decline of the wetland was the largest,which was 28,59%compared with that in 1987,and the wetland and wetland of the lake wetland and the swamp wetland were increasing.(3)The spatial change of wetland can be divided into four types:stable change,increase,decrease,increase and decrease.The spatial changes of wetland in the study area in 1987-2016 were mainly composed of 53.30%,25.15%,12.13%and 9.42%,respectively,with the increase of wetland and the change of wetland increasing and decreasing.%.(4)There are not the same to different types of wetland centroid movement direction and distance.From the movement pattern of the wetland centroid,the wetland centroid movement of the river showed a"broken line",and the wetland centroid movement of the lake showed "zigzag".The marsh wet mass movement showed "zigzag",the artificial wetland centroid movement Showing "inverted V".From the point of view of the displacement,the moving time of the five time periods is 1909.61m,2968.90m,2185.81m,1876.02m,1419.46m,respectively.The distance of the two moving distances in the study area is small,and the overall wetland center of the study area has a tendency to move to the northwest.(5)The results of landscape index analysis show that the wetland landscape in the study area is becoming more and more complicated and fragmentation.The change of plaque density and perimeter area of wetland showed an increasing trend,and the aggregation index,plaque binding index,Shannon diversity index and Shannon's evenness index were generally declining,and the connectivity between plaques And the degree of integration is reduced,and one or more landscape components are dominant in the wetland landscape,and the landscape diversity is decreasing.(6)The factors of temporal and spatial variation of wetland in the study area are mainly human activities,natural factors and water supply of the Yellow River,which constitute the main driving force of wetland spatio-temporal changes.The annual average temperature and annual rainfall value increase and the annual evaporation decreases gradually,the groundwater depth is gradually becoming smaller,the natural trend of natural factors is conducive to the development of wetlands,but the human factors interfere with the strong,although the wetland area increased,The fragmentation of the wetland landscape is increasing,the landscape connectivity and the degree of integration are reduced,so the awareness of wetland policy and public awareness of wetland protection should be further improved and strengthened.