Landfilling, a primary waste disposal strategy all over the world, is a very effective way to store carbon, almost permanently. With the tremendous urban land and population expansion over the last several decades, China produced more and more municipal solid waste and deposited it into landfills. However, the magnitude of the carbon storage in China’s urban landfills and its temporal change have remained unclear. Here, we estimated the total organic carbon (OC) stored in China's urban landfills between 1978 and 2014 using a first order dynamic model of the decomposition of organic matter, and data compiled from literature review and statistical yearbooks.
Our results showed that total OC stored in China’s urban landfills increased nearly or almost 62 folds from the 1970s to 2010s, and reached 236.0- 267.1 Tg C in 2014. Constructions waste was the largest OC pool (128.4-157.5 Tg C), followed by household waste (77.1- 86.0 Tg C), and sewage sludge was the least (25.4-29.0 Tg C). This relatively young anthropogenic pool accounted for more than 10% of the country’s urban ecosystems carbon stock and would play an increasingly significant role in the carbon balance of China's urban ecosystems. Our results echoed the findings from only existing study on urban ecosystems carbon stock including landfill pool in the Conterminous United States that carbon stored in the landfills was an important pool of urban ecosystems, and should not be neglected in the urban carbon balance and the global carbon cycle research. A consistent and continuous measurement and monitoring on delivering quantities and their fractions deposited to the landfills, and carbon contents for various wastes is the grand challenge facing to reduce the uncertainty of large scale estimations. The long term urban ecological research network, integrated with broad-scale remote sensing approach will be a key future research direction that could help address this challenge.