An overview of the municipal solid waste (MSW) management in Beijing, a city with a resident population of about 19.61 million in 2010, is presented in the article. Economic development and population growth have resulted in a MSW generation increase from 2.96 million tons in 2000 to 6.20 million tons in 2007, fluctuating to 6.35 million tons in 2010. The components of MSW over the past decade are characterized by increasing food and paper contents, and a decreasing ash content. The percentage of food waste, the main putrescible component, increased steadily from 45.77% in 2002 to 66.98% in 2010. Combustible materials, such as plastic, paper, textile, wood and food waste, accounted for 94.66% of MSW in 2008. There are 15 landfill sites, 2 incinerators and 2 composting plants in Beijing, with a total designed capacity of 15,380 tons/day in 2010. The main waste disposal technology used in Beijing is landfill, which accounts for 92.27% of the total designed capacity in 2008 and 78.54% in 2009. The designed capacity of the existing disposal plants cannot cope with the actual quantity of waste generation, resulting in overloading and premature closure of landfill sites. Solid waste incineration has been given priority in technology development and financial support over other disposal methods.
Forest ecosystems are vital to the terrestrial ecosystem’s carbon (C) cycle. The effects of nitrogen (N) addition on C sequestration in forest ecosystems are critical for better understanding C dynamics when facing an increase in N availability. We conducted a six-year field experiment to examine the effects of N addition on C sequestration and net ecosystem productivity (NEP) in a Quercus liaotungensis forest in northern China. N addition resulted in a significant increase in biomass C storage (17.54–48.62%) and changed the distribution patterns of above and belowground biomass C storage, resulting in a 9.64 to 23.23% reduction in the proportion of belowground biomass C compared with the control. The annual average heterotrophic respiration was significantly increased by the additional N (by 0.06–0.94 Mg C ha−1 yr1). In comparison with the control, the C sequestration efficiency driven by N addition ranged from 7.12 to 33.50 kg C/kg N. High-level N addition exerted stronger effects on ecosystem C sequestration than low-level N addition. NH4+-N, rather than NO3–-N, dominated the increase in ecosystem C sequestration. We found that Q. liaotungensis forest acted as a C sink. The increase in NEP in the study forest in northern China was mainly due to an increase in net primary productivity (NPP) caused by N addition. Atmospheric N deposition increased the C sequestration efficiency depending on the rate and form of N deposition.
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