Effect And Optimization Of Landscape Patterns On Soil Erosion Processes In Xinshui River Basin

Soil erosion is strongly influenced by landscape pattern.Hence,there are two methods to improve the soil and water conservation benefit,selecting suitable vegetation and optimizing land use patterns.The majority of existing research focus on the qualitative relationship between landscape pattern and soil erosion process.However,the quantitative analysis of the relationship and the landscape pattern optimization are lacking and more important.Therefore,the Xinshui River basin,a tributary of the Yellow River in Shanxi Province,is chosen as the case study area.Hydrology,ecology,soil and water conservation,statistics and meteorology are used to explore climate change,hydrology processes,land use change and landscape index variation.In addition,SWAT model is applied to analysis relationship between soil erosion and landscape pattern.The objectives of this study are:(?)to model runoff and sediment yield using landscape indexes,(?)to investigate the relationship between landscape pattern and soil erosion at the basin level,and(?)to put forward suggestions for optimization of landscape pattern.The main conclusions are summarized as follows:(1)Rainfall showed an insignificant decreased trend in 1958-2015(P>0.05).The frequency of rainstorm in the study area decreased gradually.The annual potential evapotranspiration showed a weak increasing trend,but the change trend was not significant(P>0.05).From 1958 to 2015,the mean annual runoff of the Xinshui River basin was 112million m~3,and the mean annual sediment yield was 12.8 million tons,they both showed a significant decreased trend(P<0.05).The sediment in the basin mainly came from rainstorm in flood season.Measures implemented on hillslope played the dominate role on sediment yield reduction.The sediment yield trapped by check dams in the Xinshui River basin was2.62 million tons in 1980-2015.(2)From 1987 to 2015,forest and urban and rural residential areas increased significantly,grassland decreased significantly,and farmland increased from 1987 to 2000and then decreased.On the landscape level,the landscape fragmentation increased,the shape of patches became more irregular,the aggregation decreased,the diversity and evenness decreased and the artificial disturbance became stronger.(3)Human activities played a pivotal role in runoff and sediment yield reduction in Xinshui River basin.The effect of human activities on runoff reduction was 76.31%from1978 to 2003 and 86.16%from 2004 to 2015.The effect of human activities on sediment yield reduction was 75.09%from 1978 to 2003 and 85.09%from 2004 to 2015.In order to maintain the ecological base flow,the total area of forest and grass must larger than 75%.If forest area larger than 92%,the erosion modulus will less than 1000 t/km~2 a.(4)Patch cohesion index(COHESION)and runoff showed a significant positive correlation(P<0.05).There was a significant positive correlation between Largest patch index(LPI),Interspersion juxtaposition index(IJI),Connectance Index(CONNECT)and sediment yield(P<0.05).There was a significant negative correlation between Number pf patches(NP)and sediment yield(P<0.05).(5)At basin scale,for every 10% increase in forest or grassland area in Xinshui River basin,the runoff decreased by 0.04 m~3/s and 0.02 m~3/s,respectively,the sediment yield decreased by 130 thousand tons and 100 thousand tons,respectively.For every 10%increase in farmland,the runoff increased by 0.06 m~3/s and the sediment yield increased by 240thousand tons.(6)The principles of landscape pattern regulation at small watershed scale are as follows:patch shape should develop from simplicity to complexity;patch size should change from large patch to small patch;patch distribution should change from regularity to randomness;patch aggregation of farmland should change from connectivity to separation;and patch distribution of forest should change from uniformity to dominance.