Study On Land Use Change And Soil Erosion In The Upper Reaches Of Minjiang River By Remote Sensing Technology

Currently,soil erosion is effected by natural environment and human activities as one of the main environmental issue caused by land use/cover change?LUCC?.The upper reaches of the Minjiang River,as an important tributary of the upper Yangtze River,is located on the eastern margin of the Qinghai-Tibet Plateau,and the ecosystem is particularly fragile there.Especially after the Wenchuan earthquake in2008,the extent of soil erosion in the upper reaches of the Minjiang River has become increasingly serious.Therefore,it is of great significance to study the land use change,soil erosion and the correlation between them in the upper reaches of the Minjiang River,which can provide a scientific basis for the development of scientific and reasonable land use methods to prevent soil erosion.In this paper,the upper reaches of Minjiang River was selected as the study area and the multi-stage Landsat TM/OLI remote sensing image data of the upper reaches of Minjiang River from 1990 to 2018 was taken as the data source.The land use data of the study area from 1990 to 2018 was extracted by maximum likelihood supervised classification method and its dynamic change characteristics were qualitatively and quantitatively analyzed by combining RS and GIS technology.Based on the basic data of the study area such as remote sensing image,monthly rainfall data,soil data,digital elevation model?DEM?data,the relevant factors affecting soil erosion were extracted,and the soil erosion modulus of the study area in the past 30 years was estimated by USLE equation.Then,the dynamic change characteristics of soil erosion were studied combining with the soil erosion classification standard?sl190-2007?of the study area.Based on above study,the correlation between land use change and soil erosion in the upper reaches of Minjiang River was further discussed.The main results are as follows:1)From 1990 to 2018,the land use types in the study area had been dominated by grassland and forest land.The total area of them accounted for 96%to 97%of the total land area,and the area of proportion of cultivated land was close to 3%.The maximum area of construction land and water area was less than 0.6%,and the unused land was scattered in the study area;The changes of land use area were mainly as follows:the area of construction land and water area was generally increasing,and the cultivated land area was within a certain range.The area of forest land showed a trend of rising first and then decreasing and rising at last,while the area of grassland and unused land showed a trend of decreasing fisrt and then rising and decreasing at last;The general characteristics of the transfer of land use types were mainly the mutual transformation between forest land,grassland and cultivated land as well as the conversion of forest land and grassland to water area,construction land and unused land.2)From 1990 to 2018,the types of soil erosion intensity in the upper reaches of Minjiang River were mainly micro erosion and slight erosion.The maximum area of them was 24471.15km²,accounting for 98.76%of the total area,and the minimum area of them was 23397.63km²,accounting for 94.42%of the total area;the change of soil erosion intensity was mainly reflected in the conversion of micro erosion and slight erosion,and the conversion level of soil erosion enhancement and reduction was mainly grade I to II;The average soil erosion modulus of the study area showed a trend of decreasing firstly and then rising,mainly as follows:from 1990 to 2000,the average soil erosion modulus in the upper reaches of the Minjiang River reduced216.43 t·km^-2·a^-1,while the area of micro erosion increased and the area of slight erosion to severe erosion decreased.In general,the soil erosion situation showed a recovery trend;From 2000 to 2018,the average soil erosion modulus in the upper reaches of the Minjiang River increased 624.77t·km^-2·a^-1,while the area of micro erosion decreased and the area of slight erosion to severe erosion increased.Overall,the soil erosion situation showed a deterioration trend.3)From 1990 to 2018,the severity of soil erosion corresponding to each land-use type in the study area was:unused land>cultivated land>grassland>forest land;The main land-use changes corresponding to the reduction of soil erosion in the upper reaches of the Minjiang River were the conversion from unused land and cultivated land to forest land,grassland as well as the transformation of grassland to forestland;The land-use changes corresponding to the enhanced soil erosion in the upper reaches of the Minjiang River were the conversion of forest land and grassland to cultivated land and unused land as well as the coversation of forest land to grassland.