The Dynamics Of Wetland Landscape And Its Driving Forces In Momoge Wetland

Located in western Songnen Plain,Momoge Wetland is the largest natural wetland reserve in western Jilin Province.Each year,hundreds of waterfowls come to Momoge Wetland to breed or have a break during migration.Momoge Wetland plays a significant role in the balance between water conservation supply and ecosystem in the area.Due to climate change as well as unreasonable exploitation and utilization of human activities,the area of Momoge Wetland is decreasing.Besides,the structure of the ecosystem is destroyed and the function of the system declines and even loses.Faced with serious ecological problems,Momoge Wetland draws much attention from experts and scholars to conduct surveys on the landscape changes of the wetland.At present,wetlands have carried out research on landscape,hydrology,vegetation,ecology,etc.However,there are still few studies on the interannual changes of Momoge wetland landscape from long-term sequence remote sensing images This thesis ta kes Momoge Wetland as the research object and collects the satellite remote sensing data of seasonal appearance in spring,summer and autumn over the past thirty years(the year of 1981,1989,2000,2009 and 2016).By means of object-oriented method of eCognition,the thesis automatically extracts the information of the wetland in remote sensing image(5 periods from 1981 to 2016 and 34 images in total).Through the operation platforms such as ArcGIS,FRAGSTATS and ENVI,the thesis monitors the landscape changes of Momoge Wetland for remote sensing(1981 to 2016)in the spatial structure of the wetland,transferring feature,vegetation coverage and landscape fragmentation from the perspective of area type,wetland function and landscape structure.The thesis also probes into the temporal and spatial variations as well as landscape aggregation features and reveals how the features of landscape pattern in the wetland vary with the changes of human activities by the calculation of landscape index in the scale of type and landscape.The major conclusions of the thesis are as follow:(1)Area types.As far as interannual variation is concerned,the wetland area in each period decreases compared with the wetland area in 1981.The ration of wetland area from 1981 to 2016 to the total wetland area declines from 66.24% to 47.93%.Among the wetland area,marshland occupies the largest proportion whose ration to the total area declines from 55.33% in 1981 to 27.22% in 2016.It is found according to the transferring features of land that the ratio of ploughland to the total area increases from 27.57% to 44.08%.As far as annual variation is concerned,the rate of the wetland area reaches the pea k in spring and summer.The landscape variation of wetland becomes apparent from 1981 to 1989.This is especially true in summer when marshland exchanges greatly with waters.(2)Functional changes.In spring and autumn,the vegetation in Momoge Wetland which provides food and habitat for waterfowls attracts a large amount of birds.According to the normalized differential vegetation index(hereinafter abbreviated to NDVI)of the wetland in spring and autumn,it is found that at the level of temporal variation,the NDVI in wet seasons of 1981 is higher than that of the other four periods.The vegetation coverage in dry seasons of 2016 is better than that of the other four periods.Besides,the vegetation coverage in the area increases in successive years and NDVI reaches the pea k in 2016.At the level of spatial variation,the rate of wetland area of Nenjiang River in eastern Momoge is increasing with high changing rate,while the rate of wetland area in western Momoge decreases in successive years.And the vegetation coverage is different in dry and wet seasons.(3)Landscape structures.The thesis extracts corresponding index from type scale and landscape scale and describe the landscape changes in Momoge Wetland in fractal dimension,landscape fragmentation and landscape aggregation.As to the area type,the fractal dimension of different types of landscape follows the same changing trend,in which the patch shape changes from simple to complex,the patch aggregation decreases and the landscape tends to be fragmented.What’s more,the landscape of marshland changes the most and the patch shape in marshland is the most complex.At temporal level,the fractal dimension attains minimum in 1989 and gradually increases from 1989 to 2009.From 2009 to 2016,the fractal dimension decreases and its disturbance is alleviated.However,at landscape fragmentation level,the number of patches increases and the regional landscape fragmentation is aggravated from 1981 to 2016.Besides,the aggregation among landscape patches declines and the connectivity gets worse.(4)Research area as a whole.The fastest rate of wetland degradation occurs from 2000 to 2009 and the fastest rate of marshland degradation occurs from 1989 to 2000.Besides,through the analysis of driven factors on the changes of Momoge Wetland such as natural factors,the influence of human activities and the interactions between these factors,it is found that from 1989 to 2009,human activities,which are the driven factors,retard the normal development of the original Momoge Wetland.As time goes by,the changes of the wetland get more and more interconnected with human activities whose influence on the original Momoge Wetland becomes complex with each passing day.So far,the changes of the wetland bear a close relationship with human activities and the growing increases of ploughland area play a major role in the marshland degradation of the wetland.The thesis probes into the changes of wetland landscape and wetland degradation caused by environmental problems through referring to the changing rules of landscape pattern features of Momoge Wetland in the process of interannual and annual evolution,so as to promote the recognition of Momoge Wetland.It is hoped that the thesis provides technical support and theoretical basis for the ecological protection and sustainable development of ecosystem.