| The Loess Plateau is one of the most serious soil erosion areas in China and even in the world.As a kind of ecological process,the relationship between soil erosion and landscape pattern is a scientific issue of general concern domestic and international.In recent years,the large-scale restoration of farmland to forest(grass)in the Loess Plateau and other ecological constructions have led to drastic changes in the underlying land cover structure of the region.The dynamic change of land use significantly changed the regional landscape structure and configuration,and had a significant impact on the runoff and sediment processes.Scientific understanding of the role of landscape pattern evolution on soil erosion is of great practical significance in guiding soil erosion control and ecological restoration measures deployment on the Loess Plateau.Traditional landscape pattern index is usually based on physical statistics of land use types,which fails to couple landscape pattern with ecological process and lacks certain ecological significance.In this study,taking Dali River as the study area,aiming at the process of runoff and sediment,the process-based landscape pattern index was constructed from four aspects:land use,soil properties,topography and vegetation coverage,and the field positioning observation was combined with spatial pattern analysis,identification of Dali river returning farmland to forest(grass)under the action of the evolution of the landscape pattern and its response to the process of water and sediment.The main conclusions are as follows:(1)From 1960 to 2015,the average annual precipitation in the Dalihe River Basin was 309mm,showing an insignificant increase trend,and the average annual variation coefficient of precipitation was 23.91%.The average annual runoff was 136.2 million m3,and the average annual sediment transport was 33 million t.The annual runoff and sediment transport showed a significant decreasing trend(P<0.01),and the annual runoff and sediment transport decreased by 34.85%and 89.14%,respectively.Attribution analysis showed that human activities were the main reason for the reduction of water and sediment in the Dalihe River Basin,and the contribution to water and sediment reduction reached the maximum after 2000,accounting for 98.79%and 114.67%of the measured water and sediment reduction in the base period,respectively.(2)There were significant changes in land use/cover in the Dalihe River Basin from 1990 to 2015.Under the influence of the policy of returning farmland to forest(grass),the area of cultivated land in the study area showed a trend of decline in recent 30 years,with a decrease of 139.45km2.The fluctuation of woodland,grassland and construction land increased by 38.45%,3.04%and 59.12%,respectively.From 1990 to 2015,the vegetation coverage of the basin was improved on the whole,and the annual mean vegetation coverage showed a fluctuating increasing trend,with an increase range of 53.47%.(3)From 1990 to 2015,the patch density(PD)and the Contag index(ConTAG)showed a fluctuating increasing trend.In recent years,the edge density(ED),landscape shape index(LSI),landscape DIVISION and average shape index(SHAPE—MN)showed a fluctuating decreasing trend,indicating that landscape types tended to be distributed uniformly,highly aggregated and highly connected.In the traditional landscape indices,PD,ED,LSI,SHAPE MN and CONTAG were negatively correlated with runoff modulus and sediment transport modulus in the Dalihe River Basin,while Division and AI were positively correlated with runoff modulus and sediment transport modulus in the Dalihe River Basin.The correlation coefficient between ED and runoff modulus and sediment transport modulus was-0.774 and-0.766,respectively.However,the correlation between the seven traditional landscape indexes and water and sediment did not pass the significance test.(4)A process-based water and sediment landscape pattern index(RSLI)was constructed by integrating land use,soil,topography and vegetation factors.From 1990 to 2015,the RSLI index at the landscape level decreased by 36.24%.The results showed that the vegetation restoration in the Dalihe River Basin was obvious,the soil erosion risk was gradually reduced,and the ability of water and soil conservation was continuously enhanced.The correlation coefficient between RSLI index and runoff modulus was 0.922(P<0.01),and the correlation coefficient between RSLI index and sediment transport modulus was 0.909(P<0.05).According to the influence factors of soil erosion and process,fully consider the study area of land use,topography,soil properties and vegetation coverage data influence on basin runoff process,in view of ecological processes of soil erosion and establish RSLI index and the correlation between the river basin water sand is superior to the traditional landscape pattern index,and through the test of significance,It shows that the RSLI index has a good coupling relationship with the runoff and sediment in the basin,and can better represent the runoff and sediment changes in the basin. |
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