Dynamic Change Of Soil Erosion And Ecological Safety Evaluation In The South And North Mountains Of Lanzhou City

Lanzhou is an important transportation hub and logistics center in northwest China,as well as an important node city on the Silk Roads.The North and South mountains are the ecological protection barrier and an important part of the ecosystem of Lanzhou.In this paper,five soil erosion factors in the RUSLE model are firstly calculated.Secondly,the RUSLE model was used to calculate the soil erosion modulus of the North and South mountains in Lanzhou city.And the spatial and temporal dynamic changes of soil erosion and the soil erosion characteristics under different environmental factors were analyzed.Finally,the ecological security evaluation system is constructed based on the DPSIR model and the ecological security of the North and South mountains of Lanzhou city is graded.The countermeasures for the benign development of ecological security are proposed.The results show that:(1)In terms of precipitation erosivity factors,the average precipitation erosivity factor R values of the North and South mountains in 1995,2000,2005,2010,2015and 2018 were 110.06,83.20,71.09,46.68,56.97 and 198.61MJ·mm/(hm~2·h),respectively.Spatially,in 1995,2000,2005 and 2010,the precipitation erosivity of the South and North Mountains decreased from southeast to northwest,and the southeast was larger than the northwest.In 2015 and 2018,the precipitation erosivity factors of the South and North Mountains decreased from west to East,and the West was larger than the East.In terms of soil erodibility factors,the area of soil vulnerable to erosion in the South and North Mountains of Lanzhou city is 1887.01km~2,accounting for94.63%,and the whole soil of the South and North Mountains of Lanzhou city is vulnerable to erosion.The gradient slope and slope length factor of South and North Mountains in Lanzhou city is zonal distribution,and the gradient slope and slope length factor of South Mountain is significantly longer than that of North Mountain.In terms of vegetation coverage and management factors,in 1995,2000,2005,2010,2015 and 2018,the average vegetation coverage and management factor C values of the South and North Mountains in Lanzhou were 0.34,0.43,0.56,0.50,0.40 and 0.57,respectively.In the aspect of erosion control practice factor,the spatial distribution of erosion control practice factor in the South and North Mountains of Lanzhou is relatively consistent,and the change is not obvious.(2)In 1995,2000,2005,2010,2015 and 2018,the average values of soil erosion modulus of the two mountains in Lanzhou were 16.59,16.24,17.16,10.04,15.77 and25.83t/(hm~2·a),respectively.The average annual soil erosion amount was 330.74×10~4t,323.80×10~4t,342.09×10~4t,200.20×10~4t,314.41×10~4t and 515.14×10~4t.From 1995 to2018,the average soil erosion modulus of the North and South Mountains in Lanzhou showed a fluctuating downward trend.In 1995,2000,2005,2010,2015 and 2018,the soil erosion intensity of the South and North Mountains in Lanzhou city was mainly micro erosion,which was distributed in the northwest and southeast of the North and South mountains.The strong,extremely strong and intense soil erosion are mainly distributed in the central part of the North and South mountains.(3)Soil erosion shows different erosion characteristics under different environmental factors.With the increase of altitude,the soil erosion modulus first increases and then decreases.With the increase of slope,the soil erosion modulus increases.The average soil erosion modulus of grassland and forest land is larger,and the average soil erosion modulus of water area is the smallest.The soil erosion modulus of medium and low vegetation is the largest,except for bare land,the average soil erosion modulus decreases with the increase of vegetation coverage.The soil erosion modulus in the green area is higher than that in the ungreen area,which is mainly the result of the comprehensive action of soil,topography and vegetation in the green area.The soil erosion modulus of calcic soil is the largest,and that of semi leaching soil is the smallest.According to the results of the factor detection in the geographical detector,topography has become the main factor of soil erosion in the South and North mountains of Lanzhou city.(4)In 1995,2000,2005,2010 and 2018,the South and North Mountains dominated the areas with less ecological security.While in 2015,the South and North Mountains dominated the areas with more ecological security.On the whole,the unsafe area shows a fluctuating downward trend.The safer area shows a fluctuating upward trend.The safe area shows a fluctuating upward trend.The ecological security situation of the two mountains in the South and the North has improved significantly.