中国食品源氮消费环境排放及其城乡差异

食品源氮消费是人居环境养分流动的重要环节,中国食品源氮消费产生的环境排放受城乡二元结构影响在时空变化上呈现显著分异。基于物质流分析方法,从中国城乡食品消费后产物不同处理过程及其对氮代谢的影响出发,模拟氮物质代谢过程,构建了一套氮素环境排放计算模型,借以研究中国近20年来城乡食品源氮消费环境排放趋势变化及其差异。研究结果发现1993—2012年间,我国城乡居民人均食品源氮排变化轨迹迥异。同时,城乡食品源氮消费在其所造成的水体、土壤、大气环境负荷中扮演的角色各不相同:在水体环境负荷中,农村水体氮排占据主导地位,但城乡间差异正逐步缩小;在土壤环境负荷中,城市土壤氮排主导优势明显;2010年以前全国食品源氮消费大气环境负荷主要受农村气体氮排的影响,而2010年以后,城市大气氮排成为影响全国大气氮负荷的主导因素。引入社会经济因素分析后发现,城镇居民人均可支配收入水平对城镇居民人均食品源氮排起显著促进作用;而农村食品价格指数对农村居民人均食品源环境氮排呈显著抑制作用。通过情景预测分析发现:随着我国城镇化进程的加快,未来全国居民人均食品源氮排将以更快速度继续增长。

Environmental emissions of nitrogen from food consumption and differences between urban and rural areas in China

Consumption of nitrogen in food forms an important part of the internal flow of nutrients within human settlements. Spatiotemporal variation in the environmental emissions of nitrogen from food consumption vary considerably between the city and countryside because of the dual economic structure of urban and rural areas. In this study, we used substance flow analysis to simulate the metabolism of nitrogen and constructed a set of models to calculate the quantity of environmental emissions from the consumption of nitrogen in food. The models focused on the different levels of resource recycling of the product after metabolism to determine the trends in environmental emissions of nitrogen from food consumption and the differences between urban and rural areas. The results indicated there was a substantial difference between trends in urban and rural environmental emissions of nitrogen consumed in food from 1993 to 2012. The roles of consumed nitrogen in urban and rural areas, which consisted of the environmental loads in water, soil, and the atmosphere, varied from each other. In terms of water nitrogen loads from food consumption, nitrogen in rural water played a dominant role. However, the difference in nitrogen emissions in water between the city and countryside was gradually decreasing. Regarding soil nitrogen environmental loads from food consumption, nitrogen in the urban soil was the dominant factor. Prior to 2010, the rural atmospheric nitrogen emission was the main factor that influenced the national level of atmospheric nitrogen emissions because of food consumption. Nevertheless, after 2010, the quantity of urban atmospheric nitrogen emissions exceeded that of rural areas, and became the leading factor of the national level of atmospheric nitrogen emissions. Additionally, correlation analysis was adopted to determine whether a positive correlation existed between per capita disposable income and per capita urban resident environmental emissions of nitrogen from food consumption. In addition, the per capita rural resident environmental emissions of nitrogen from food consumption was negatively correlated to the food price index. Based on scenario forecast analysis (SFA), we found that the growth of future national levels of per capita nitrogen emissions from food consumption would be faster than the current trend because of the acceleration of urbanization in China.