The Influence Of Land Use Transformation On Soil Carbon Storage In The Tableland Of The Loess Plateau Of Shaanxi Province During The Last Thirty Years

The long–term dynamic changes of soil organic carbon in the regional scope are essential for the concentration of atmospheric greenhouse gases and the ecological effects of the local environment.The impact of regional land use type change on soil organic carbon storage is the core issue of ecological environmental impact assessment.Based on soil samples and land use data,this paper studied the spatial distribution characteristics of soil organic carbon density in the surface layer(0–20 cm)of the Loess Plateau in Shaanxi Province in the past 30 years,and the relationship between climate,topography,soil type,land use and soil organic carbon density and reserves was discussed.The research results are as follows:?The soil organic carbon density and storages of the Loess Plateau increased in the past three decades.The soil organic carbon density was significantly correlated with temperature,soil type and land use at P<0.001,and was significantly correlated with precipitation at P<0.05.?From 1985 to 2015,with the increase of temperature and precipitation,the density of soil organic carbon showed an increasing trend.As the elevation and slope increases,the organic carbon density showed a tendency to increase first and then decrease,and reaches the maximum in the range of 679–779 m and 10–20°.The organic carbon density and storages of most soil types increase with time,among which the soil organic carbon density of the Black loam is the largest(1.59 kg/m~2),the highest storage capacity of the Yellow soil increases by 5.64×10~6 t.The organic carbon density and storages of different land use types increase with time.The organic carbon density of forest grassland is obvious higher than that of cultivated land.?The policy on converting farmlands to forests accelerated the speed of land conversion of land use types in the study area.The land use conversion rates of cultivated land from 1985 to 2006 and 2006 to 2015 were 2.81%and 17.89%,respectively.The changes in surface organic carbon density of cultivated land over the past three decades in the study area were quite different.The organic carbon density was 1.73 kg/m~2 in 1985,and this increased by 8.09%in 2006 and 36.36%in 2015.?From 1985 to 2006,the areas of cultivated land remained unchanged and changed were respectively 9 429.87 km~2 and 272.41 km~2;And the increased soil organic carbon storage were 927.93×10~6 kg and 33.8×10~6 kg,respectively.From 2006 to 2015,the areas of cultivated land remained unchanged and changed were 8 119.04 km~2 and 1 768.47 km~2,respectively;the increased soil organic carbon storage were 3 132.79×10~6 and 1 198.99×10~6kg,respectively.?From 1985 to 2006,the area of land use type remained unchanged and changed to12 011.65 km~2 and 774.33 km~2,respectively.And the increased soil organic carbon storage was 1 406.02×10~6 kg and 14.29×10~6 kg,respectively.From 2006 to 2015,the area of land use remained unchanged and changed,which were 9 376.13 km~2 and 3 400.52 km~2,respectively.Meanwhile the increased soil organic carbon storages were 3 383.77×10~6 kg and 1 316.64×10~6 kg,respectively.It was conducive to the formation of surface soil carbon sinks when the land use type turned to forest land and grass land;It caused the release of surface organic carbon when land use type changed to cultivated land,residential land.?The critical value of soil organic carbon rising or falling in different regions was different.Xi'an was the largest(3.04 kg/m~2);Tongchuan was the lowest(2.09 kg/m~2).For the saturation level of soil carbon pool,Xi'an had the highest level of 3.04 kg/m~2;Tongchuan had the lowest level of 2.09 kg/m~2.The saturation level of the entire loess platform was 2.71kg/m~2.From the total carbon sequestration potential,Weinan was the highest(6.20 Tg);Tongchuan was the lowest(0.12 Tg).From the carbon sequestration potential per unit area,Baoji is the highest(1.05 kg/m~2);Xi'an,Weinan and Xianyang were next,while Tongchuan was the lowest(0.41 kg/m~2).The soils in the five cities of the Loess Plateau were carbon sinks.It was estimated that the carbon sequestration potential of the loess platform was 12.37Tg.