| Based on the data of soil organic matter, top layer thickness and soil texture collected and analyzed in the second survey of sample soil in 1983 and the survey of sample farmland capability in Tong'an district, Xiamen in 2006, the database of Carbon storage and carbon density raster space in the plough horizon of farmland soil in Tong'an district in 1983 and 2006 is evaluated and established respectively in this study through GIS and mathematical model combining with soil bulk density of different textures. The carbon value of the soil of plough horizon in Tong'an district is calculated by means of damage evaluation method, cost reduction method, market price, shadow price and replacement cost. In addition,, the database of carbon value raster space of the farmland soil in Tong'an district in 1983 and 2006 is also established respectively. Then the temporal and spatial variation of carbon storage, carbon density and carbon value in this district is analyzed and the division is evaluated. The result of the study reveals the follows:In 1983 and 2006, the carbon density of the soil of plough horizon in Tong'an district was between 1.004 kg/m2～4.208 kg/m2 and 0.351 kg/m2～3.781 kg/m2 respectively and the average was 2.179 kg/m2 and 1.758 kg/m2 respectively. The spacial variation of carbon density in the whole district is distinct. The towns with lower carbon density include Wuxian, Hongtang, Xinmin Town and Fengnan farm in the southeast. The towns with higher carbon density include Lianhua and Tingxi town in the northwest and Xike town in the south. In Tong'an district, the carbon density was higher in the northwest and lower in the southeast in both 1983 and 2006.The total carbon storage of the soil of plough horizon in Tong'an district was 2.25×108 t and 1.82×108 t in 1983 and 2006 respectively. The spacial variation of carbon storage was also distinct. In 1983, the towns with higher carbon storage are mainly Lianhua and Tingxi town in the northwest where the carbon storage takes up 50.24% of the total. In 2006, the towns with higher carbon storage include Lianhua, Wuxian and Tingxi town where the carbon storage takes up 64.11% of the total and the spacial division was also higher in the northwest and lower in the southeast.In Tong'an district, the total carbon value of the soil of plough horizon in 1983 and 2006 was $4.735 billion and $3.820 billion respectively. The spacial variation of carbon value is distinct. In 1983, the carbon value difference in each town is between $700 million and $1.503 billion with the average of $592 million. The towns with higher carbon value are Lianhua, Tingxi and Wuxian town. In 2006, the carbon value difference in each town is between $680 million and $1.074 billion with the average of $478 million. The towns with higher carbon value also include Lianhua, Wuxian and Tingxi Town. The carbon value was also higher in the northwest and lower in the southeast.In Tong'an District, the area with higher carbon density, which mainly located in Tingxi and Lianhua Town, accounted for 11.71﹪and 1.95﹪of the total cultivated land respectively in 1983 and 2006 and the density of carbon in the soil was 3.486 kg/m2 and 2.823 kg/m2 respectively. While the area with medium carbon density, which mainly located in Tingxi, Lianhua and Xinmin Town, accounted for 62.44﹪and 72.06﹪of the total area respectively in 1983 and 2006 and the density was 2.439 kg/m2 and 1.901 kg/m2 respectively. The While the area with lower carbon density accounted for 28.85﹪and 62.13﹪respectively in 1983 and 2006 and density was 1.760 kg/m2 and 1.385 kg/m2 respectively. These areas located in Wuxian and Hongtang Town in 1983 and in Wuxian and Lianhua Town in 2006.In Tongan district, the area with higher carbon reserve took up 15.04% and 2.88% of the total arable land respectively in 1983 and 2006 and the average carbon reverve was 34.42 t/hm2 and 27.11 t/hm2 respectively. This area mainly located in Tingxi and Lotus Town. The area with medium carbon reserve took up 53.36% and 30.86% of the region's total area of arable land respectively in 1983 and 2006 and the average carbon reserve was 24.33 t/hm2 and 18.96 t/hm2 respectively. This area mainly located in Lianhua town in 1983 while in Lianhua and Tingxi Town in 2006. The area with low carbon reserve mainly located in Wuxian and Hongtang Town in 1983 and in Wuxian, Lianhua, Xinmin and Hongtang Town in 2006 accounted for 31.60% and 66.26% of total area of arable land in this region in 1983 and 2006 respectively. The average carbon reserve was 17.66 t/hm2 and 14.06 t/hm2 respectively.In Tong'an district, the farm land area with higher carbon value were 1450.85 hm2 and 246.31hm2 in 1983 and 2006 respectively, which took up 12.76﹪and 2.17﹪of the total farm land area respectively. This kind of farm land was mainly located in Tingxi and Lianhua Town. The area with medium carbon value was 6491.74 hm2 and 3788.86 hm2 in 1983 and 2006 respectively, which took up 57.09﹪and 33.32﹪of the total farmland respectively. In 1983, this area mainly located in Lianhua, Xinmin and Wuxian town, while in 2006, it mainly located in Lianhua, Wuxian, Tingxi, Hongtang and Xinmin town,and Datong and Xiangping street. The area with low carbon value was 3428.72 hm2 and 7336.13 hm2 in 1983 and 2006 respectively, which took up 30.15﹪and 64.51﹪of the total farm land area respectively. In 1983, this kind of farm land mainly located in Wuxian, Hongtang, Xinmin town and Datong and Xiangping street. In 2006 it mainly located in Wuxian, Lianhua , Xinmin and Hongtang town.During 1983 and 2006, there was an obvious change of the carbon density and carbon storage of the arable layer of the farm land in Tong'an district with a general trend of descending. The area with an increasing carbon density took up 16.21 % of the total farm land while the area with a decreasing carbon density took up 83.73 %. The towns where carbon density increased significantly mainly included Wuxian, Xike, Hontang and Datong and Xiangping street while those with significantly decreasing carbon density mainly included Lianhua, Tingxi and Xinmin town. In the last 23 years, the carbon density of the farm land arable layer across the district took on such a trend: the density in part of the land in southeast had somewhat increased while the density in most part of the northwest had somewhat decreased. The change of carbon storage was completely consistent with the change of the carbon density. In the last 23 years, the carbon value in the unit area and the total value of the farmland were both decreased in a different degree. The farmland where the carbon value increased took up 14.34 % of the total farmland and the carbon value increased significantly in Wuxian, Hongtang and Xinmin town and Datong and Xiangping street while the carbon value in Lianhua and Tingxi town decreased significantly. The change of the carbon value in a unit area and that of the carbon density are generally the same. |
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