Effect Of Land Use Pattern Change On Soil Erosion In Small Watersheds Of The Hilly And Gully Regions On The Loess Plateau

In recent decades,the impact of human activities on land use patterns has been increasing,resulting in many new environmental problems.For example,the impact of land use change on soil erosion and runoff and sediment transport has been a hot topic for scholars at home and abroad.Therefore,it is of great significance to research land use change in the vulnerable areas of ecological environment for the rational use of land resources and the construction of ecological environment.Taking Zhifanggou watershed in Loess Hilly and gully region as the research object,the land use data,soil type data,measured rainfall,runoff and sediment transport data of Zhifanggou watershed from 1938 to 2020 were obtained.Combined with the field investigation of soil and water conservation measures in Zhifanggou watershed,the "3S" technology analysis method was used to establish the land use change dynamic model of Zhifanggou watershed from 1938 to 2020 State database.The WaTEM/SEDEM model was used to simulate the erosion and sediment yield process of the Zhifanggou watershed,and further study the impact of land use changes in the Zhifanggou watershed on soil erosion;Fragststs was used to calculate the Zhifanggou watershed landscape index,and the Zhifanggou watershed landscape index and erosion yield were established.The relationship between sand reveals the response of the erosion and sediment yield of the Zhifanggou watershed to changes in the landscape index.The main conclusions are as follows:(1)The main land use types in the Zhifanggou watershed from 1938 to 2020 are arable land,woodland and grassland.The total area of the three land use types exceeds 85% of the total area of Zhifanggou watershed in each year.From the dynamic change of land use,the area of cultivated land,grassland,garden and unused land in Zhifanggou watershed increased first and then decreased.The area of woodland decreased sharply from 1938 to 1958,and then gradually increased after 1958.The area of construction land has been in an upward trend.From the perspective of land use transfer,from 1938 to 2020,the land use of Zhifanggou watershed experienced a stage of high vegetation cover low vegetation cover high vegetation cover;From 1938 to 1958,Zhifanggou watershed changed from high vegetation cover to low vegetation cover,and the land use transfer mainly occurred in the transformation from woodland to cultivated land;From 1958 to 1978,the vegetation increased slowly,the spatial distribution of land use did not change dramatically,and the transfer of land use was not obvious;From 1978 to 2020,the vegetation is in the stage of steady improvement.Due to the implementation of afforestation and the project of returning farmland to forest and grassland,the vegetation coverage of Zhifanggou watershed has increased significantly.The main land use mode is the transfer of cultivated land and unused land to woodland,grassland and garden.(2)From 2000 to 2010,the runoff and sediment transport in Zhifanggou watershed showed a decreasing trend year by year,and there was no obvious correlation between the annual runoff and sediment transport and the annual rainfall.The results show that the rainfall in Zhifanggou watershed has not changed significantly in recent years,and the decrease of runoff and sediment discharge is greatly affected by the change of landscape pattern caused by human activities.From 1938 to 2020,the intensity of soil erosion in the Zhifanggou watershed showed the characteristics of first intensifying and then weakening.In 1938,the Zhifanggou watershed was mainly slightly eroded.The period from 1958 to 1994 was mainly violent erosion and extremely strong erosion.From 1999 to 2020,the erosion intensity gradually changed into slight erosion and mild erosion.The main areas of severe erosion and extremely severe erosion in Zhifanggou watershed are cultivated land and garden land.From1938 to 2020,the average erosion intensity of cultivated land changed from severe erosion to mild erosion.The average erosion intensity of the garden changed from severe erosion to severe erosion.The sedimentary areas are mainly distributed in woodland and grassland.(3)From 1938 to 1994,the landscape pattern of Zhifanggou watershed tended to be fragmented.The landscape types increased,and the landscape dominance decreased.After1994,the patches gradually integrated;the aggregation degree increased;the landscape types decreased;and the dominant landscape types gradually highlighted.Among all landscape types,grassland was the most fragmented landscape type in 1938.After 1958,the landscape fragmentation and landscape heterogeneity of each landscape type experienced a process of first increasing and then decreasing.From 1987 to 1994,cultivated land was the most fragmented landscape type.The dominant landscape types in Zhifanggou watershed are mainly forest land,cultivated land and grassland.In 1938,the dominant landscape type was woodland.In 1958,the area of woodland decreased and the area of cultivated land increased.The dominant landscape type was converted to cultivated land.After 1958,the dominant landscape species transferred from cultivated land to woodland and grassland.Although the patches of different landscape types were fragmented and dispersed,the landscape patch structure of Zhifanggou watershed was dense and connected well during the whole study period.Since 1999,due to the intensification of human activities,plaques have gradually integrated to form dense large plaques,and the complexity of plaque shape has decreased significantly.(4)Through Pearson correlation analysis,PAFRAC and IJI are significantly correlated with the erosion modulus of the watershed(P<0.01).The relationship model between erosion modulus and LPI,perimeter-PAFRAC,IJI,COHESION and SHEI is established,and the model has high accuracy.