Land-use induced changes in topsoil organic carbon stock of paddy fields using MODIS and TM/ETM analysis: a case study of Wujiang County, China.

Topsoil soil organic carbon (SOC) that plays an important role in mitigating atmospheric carbon dioxide (CO2) buildup is greatly affected by human activities. To evaluate the influence of land-use changes on SOC stocks in paddy soils, a new algorithm was developed by integrating MODIS (moderate resolution imaging spectral-radiometer) and TM/ETM data for timely monitoring the land-use change in Wujiang County. Thereafter, the land-use class-maps derived from MODIS and TM/ETM analyses were further used to estimate land use-induced carbon (C) pool changes in paddy topsoil of Wujiang County based upon the nationwide arable soil monitoring data and county level SOC reconnaissance data in 2003. The results showed that irrigation-based rice cultivation in Wujiang County has resulted in SOC content at an annual increasing rate of 0.01 g/kg over the period of 1984-2003, while the density of SOC in uplands and woodlands has decreased. Annual decreasing rate of SOC content was estimated to be 0.03 g/kg in uplands and 0.06 g/kg in woodlands. The total topsoil SOC stocks in paddy fields of Wujiang County have increased from 2.67 x 10(6) t C in 1984 to 2.69 x 10(6) t C in 2005. During 1984-2005, the total SOC sequestrations in rice paddies were greater than the SOC losses in woodlands and uplands. The temporal C loss might have exceeded the SOC sequestration in rice paddies due to their conversion to nursery lands and uplands since 2001. The results of this study suggest that changes of land use have a great influence on soil C sequestration, particularly on C stocks and C sequestration potential in paddy fields in developed areas of China.