It demonstrates that carbonate accumulation greatly exceeds organic carbon in both soil and sediment. It also shows that intensive cropping with sound land management in the arid land not only increases soil organic carbon stock, but also enhances accumulation of soil carbonate, particularly in subsoils. Carbon accumulation in the lake sediment increased between 1950 and 2000, after which it declined, and the authors explore how human activity and climate change may have caused the changes in carbon burial in the lake sediment.