农业表层土壤碳库容易受人为强烈干扰,而又可以在较短的时间尺度上进行调节,当今我国经济发达地区土地利用变化必然会对土壤固碳产生重要影响。本研究以江苏省吴江市水稻土为例,利用新一代中分辨率成像光谱仪(MODIS)和TM/ETM影像提取了1984年稻田面积,以及这部分稻田在2000-2005年的土地利用变化状况。研究中以最大似然法对TM/ETM、MODIS影像应用归一化植被指数(NDVI)、增强型植被指数(EVI)和陆地水分指数(LSWI)掩膜的方法作了识别提取;同时,结合第二次全国土壤普查、2003年耕地地力调查点和吴江市农林局土肥指导站长期定位点的土壤有机碳数据估算了1984年和2000-2005年土壤碳库变化情况。结果表明:近20多年来尽管吴江市水稻土水耕熟化过程中有机碳总体呈增加的趋势,但由于大量稻田被非农用地所取代,导致土壤固碳能力大幅度下降,尤其从2001年开始从"碳汇"变成"碳源"。因此,在我国经济发达区应密切关注耕地转换成非农用地而导致的土壤有机碳的损失。

Soil organic carbon (SOC) storage is an important parameter of soil environmental quality, and agriculture soil is easy to be interfered by human activities and also could be adjusted in a short time scales. The ongoing land-use changes in developed area in China have important influence on SOC (soil organic carbon) sequestration. In this research we take Wujiang County as a case, evaluated the influence of land-use changes on the soil carbon sequestration ability in the paddy fields. The land use classification in Wujiang County from 2000 to 2005 were conducted by a new methodology that integrates 8-day composite images (500-m and 250-m spatial resolution) from the moderate resolution imaging spectro-radiometer (MODIS) sensor with Landsat data. The maximum likelihood classification (MLC) method was used to conduct TM/ETM images classification. The vegetation index (NDVI, EVI) and land surface water index (LSWI) mask method was used to conduct MODIS images classification. The land use class map and the density of soil organic carbon (SOC) data from the 2nd State Soil Survey and the nationwide arable soil monitoring system (NASMC) along with county-level soil reconnaissance data were further used to calculate the soil carbon sequestration ability. The result showed that irrigation-based rice cultivation in the study area has induced significant enrichment of SOC storage in paddy soils. But carbon sequestration ability tended to decline over the most recent six years due to decreasing in paddy area and shifting to other land uses. The paddy soils have switched from carbon sink to carbon source since 2001. The total SOC sequestration in 0-15cm soils in 1984, 2000, 2001, 2002, 2003, 2004 and 2005 were 107×10³t,9.2×10³t,-8.0×10³t, -21.2×10³t,-49.2×10³t,-41.6×10³t and -49.4×10³t respectively. The results of this study suggested that land use changes have a great influence on topsoil carbon (C) sequestration, particularly on C stocks and C sequestration potential in paddy fields in developed areas of China.