Quantitative Estimation Of Soil Conservation Capability Of Grasslands In The Qilian Mountains

To explore the soil conservation capability of grasslands in the Qilian Mountains,field investigation were set to survey the characteristics of vegetation and soil loss in the grasslands.And correlation analysis and path analysis were used to research the effect of vegetation coverage and biomass on soil erosion of grasslands in the Qilian Mountains.Depending on that,a new evaluation model identified by vegetation coverage and biomass was built to modify the biological measure factor(B)in Chinese soil loss equation(CSLE).Through combining field surveys with remote sensing observations,the spatial distribution characteristics of vegetation coverage and biomass of grasslands in the Qilian Mountains were analyzed,and soil erosion amount and soil conservation capability of grasslands in the Qilian Mountains were estimated based on the modified evaluation model of B factor,CSLE and geographic information system(GIS).It provides reference for soil erosion research and ecological benefit evaluation in the Qilian Mountains.The main results are as follows:(1)Soil erosion was positively correlated with vegetation coverage,below-ground biomass,and soil sand content at P<0.01,negatively correlated with slope and soil silt content at P<0.01,and positively correlated with vegetation diversity and above-ground biomass at P<0.05.Path analysis showed that vegetation coverage and below-ground biomass were crucial factors for soil erosion of grasslands in the Qilian Mountains.The direct and indirect path coefficients of vegetation coverage were-0.660 and-0.075 respectively,and the direct and indirect path coefficients of below-ground biomass were-0.286 and-0.174 respectively.This indicates that the influence of vegetation coverage on soil erosion was mainly an intense direct effect,whereas the influence of below-ground biomass had a weaker direct effect,and there were quite a few non-negligible indirect effects on soil erosion of below-ground biomass.Soil loss increased obviously with vegetation coverage and below-ground biomass,exponential functions could be used to express the relationship between the sediment yield of surface runoff and vegetation coverage,below-ground biomass.(2)The vegetation coverage of grasslands in the Qilian Mountains showed a very large spatial difference with an increasing trend from the west to the east.The vegetation coverage in the western grasslands was mainly less than 10%,and the vegetation coverage in the central grasslands was about 30%-60%,while the vegetation coverage in the eastern grasslands was more than 60%mostly.The spatial distribution pattern of grassland biomass was consistent with the vegetation coverage,which also showed an increasing trend from the west to the east.During the growth season in 2015,the average above-ground biomass of grasslands in the whole Qilian Mountains was 81.92g/m2,as well as the average below-ground biomass of grassland in the whole Qilian Mountains was 611.94 g/m2.The average above-ground biomass and below-ground biomass of grasslands in Da Qaidam and Delhi located in the west of Qilian Mountains were less than 60g/m2 and less than 400 g/m2 respectively While the average above-ground biomass and below-ground biomass of grassland in Huzhu,Datong,Ledu located in the east of Qilian Mountains were generally more than 100 g/m2 and more than 800 g/m2 respectively(3)The exponential multiple regression model could well express the relationship between B factor and vegetation coverage(x1),below?ground biomass(x2).The expression of the most optimal model is B=e-0.037x1-0.094d2(R2=0.951).According the estimation results of B factor by the modified evaluation model and the traditional coverage-B model,the estimation effect of modified B factor model is superior to the traditional coverage-B model which made smaller results in the grasslands with low vegetation coverage in the Qilian Mountains.Moreover the soil erosion modulus estimated by the coverage-B model is generally smaller than that estimated by the modified B factor model,and the difference is even more in the grasslands with intense soil erosion.(4)The average soil erosion amount of grasslands in the whole Qilian Mountains in 2015 was 475.13 t/km2,and the soil erosion amount of grassland in different counties varied from 200 to 700 t/km2.The grasslands with large erosion amount were concentrated in Tianjun,Menyuan,Datong and Minhe while the grasslands with small erosion amount were concentrated in Da Qaidam and Delhi.The grasslands with the soil erosion amount of 0-200 t/km2 accounted for about 49%of the total grassland areas.The average soil erosion amount in the whole Qilian Mountains in 2015 was 351.91 t/km2,and the soil erosion amount in different counties varied from 100 to 750 t/km2.The areas with large erosion intensity were concentrated in Tianjun,Menyuan,Datong and Minhe while the areas with weak erosion intensity were concentrated in Da Qaidam and Delhi.The areas with the soil erosion amount of 0-200 t/km2 accounted for about 67%of the total areas.(5)The soil conservation capability of grassland in the Qilian Mountains showed a very large spatial difference with an increasing trend from the west to the east.The average soil conservation capability of grassland in the whole Qilian Mountains in 2015 was 1601.36 t/km2,and the soil conservation capability in different counties varied from 30 to 6000 t/km2.The grasslands with the soil conservation capability below 200 t/km2 accounted for 54%of the total grassland areas,while the grasslands with the soil conservation capability above 15000 t/km2 accounted for just 1.41%of the total grassland areas.The soil conservation capability in the Qilian Mountains showed a very large spatial difference with an increasing trend from the west to the east.The average soil conservation capability in the whole Qilian Mountains in 2015 was 1241.18 t/km2,and the soil conservation capability in different counties varied from 10 to 4500 t/km2.The areas with the soil conservation capability below 200 t/km2 accounted for 63%of the total areas,while the areas with the soil conservation capability above 15000 t/km2 accounted for just 1.03%of the total areas.