Spatial Distribution And Reserves Estimation Of Soil Organic Carbon Based On GIS In Maiji Area Of Tianshui

Soil carbon is an important part of the carbon cycle in terrestrial ecosystem. According to estimation, the soil organic carbon storage in the superficial earth of 1m depth is about 1500 ~ 2000Pg (1Pg = 1015g), which is as about twice as the content of CO2 in atmosphere. Soil carbon's 0.1% change will result in parts per million change of the CO2 concentration in atmosphere. In domestic and foreign researchers'studies, the achievement of soil organic carbon pool in small and medium-scale geographical unit is still few and far between. Therefore, it's of great significance to study the spatial distribution and reserves estimates of soil organic carbon. What's more, it's much more significant to study the spatial distribution and reserves estimates of the soil in sub-humid and semi-arid areas.In this thesis, Maiji area in Tianshui is the studied area. The author studied the features of the soil organic carbon's content spatial distribution according to the datum of the 65 soil types of profiles in the second census in 1981 and 6060 measured profile of the topsoil of 20cm depth in Tianshui Maiji area in 2008 as well as the basic map information used for analyzing such as soil sampling points map, administrative map, status map and soil map etc. Kriging optimal interpolation and Mapgis software are usesd to conduct interpolation analysis of the limited profile points in the studied area. Use the soil types method for calculating soil layer deposition, wheat field, and the 1m deep and 2008 field measurement of the density of organic carbon and reserves. As follows:(1) Analysis of the Kriging interpolation and spatial distribution. This critical makes analysis of the spatial interpolation to soil organic carbon content by using the optimal Kriging method, the purpose is to overcome the false of fewer profile points and visually see what is the spatial distribution of soil organic carbon trend. Kriging interpolation results show that the same soil layers in different parts of soil carbon content exist significant difference. Overall, the soil surface and depth within the field of 1m, soil organic carbon content distribution is that low-lying hills and southeastern Qinling are higher, but the LiangMao loess plateau of organic carbon content is lower, and with the increase of depth of soil, organic carbon content of soil dicreased, and then analyze the cusses of the content of soil organic carbon in the spatial distribution.(2) Soil organic carbon density in the calculation and discussion. By computing the every hinds of the soil organic carbon density, overall, the soil of Maiji area have low average density, when soil secondary census, depths of 5cm,20cm,1m average density of organic carbon are0.92kg·m-2,3.31kg·m-2,7.79kg·m-2 respectively, average density of organic carbon at depth of 20cm is 2.43 kg·m– 2 in 2008 years, As a standard of YuDongSheng's (2005) estimation of average density of 9.60 kg·m-2 in the depth of 1m all over the China, Maiji area 1m deep soil organic carbon density is lower 1.91kg·m-2than the average density of whole country. From the map of soil carbon density spatial distribution and the content of soil organic carbon in the graph, that Maiji area organic carbon density distribution is difference. Soil organic carbon is similar to the general characteristics in the spatial distribution of density, from southeast to northwest present decreasing trends. Soil organic carbon density is higher in three mainly township: Sancha township, Dongcha township, Liqiao township. The soil type having higher soil organic carbon density is Mountain brown loam, mountainous brown soil; lower soil types, which are clay soil, deposit soil.(3) Soil organic carbon reserves estimation methods and results are discussed. At first, introducing the present soil carbon reserves estimation of the four main methods, and the comparison. Due to the soil types method is good at estimation of analysis of carbon of uncertainty in elements, which is convenient to collect and contrast form a unified system for the estimation with global soil classification system. Therefore, this study adopted the law of soil types, according to the study area adopted to calculate for unit cultivates the reserves of soil organic carbon in the soil, then add the reserves of soil organic carbon ,this treatment can be more precise to get the soil organic carbon deposition wheat reserves value. The calculation of the secondary survey, reserves of organic carbon in surface soil (0-5cm) is about 4.83×106t, reserves of organic carbon in fall (0-20cm) is about 12.46×106t, reserves of soil organic carbon in 1m depth is about 45.17×106t, reserves of soil organic carbon in fall (0-20cm) is about 18.55×106t in 2008 years. The highest reserves of soil organic carbon is brown earth, but due to the influence of human land use patterns, brown soil decreased a lot. With the destruction of forests, land reclamation and expanding forest grassland, turning forests into grasslands, the brown soil has changed into farming brown soil gradually.