长江经济带农业种植-消费系统氮流时空格局演化规律与驱动机制

针对农业农村氮过量使用产生的环境污染问题，采用物质流分析和空间分析方法，评估长江经济带农业种植-消费系统氮流时空格局演化规律及驱动机制。结果表明，1998年无机氮肥的输入量为1.088 5×10¹⁰ kg N，此后以1.14%的速度增长，2012年无机氮肥施用量开始减少，虽然2018年低于1998年水平，但无机肥施用仍是长江经济带农业种植子系统氮输入的主要来源，为其他路径氮输入总量的1.6倍。通过作物收获形式输出系统的有效氮量，并未受氮素输入波动的影响，2018年作物收获量分别比1998年和2008年高18.97%和25.71%。近几年长江经济带生猪养殖量有下降的趋势，但是受粪便及垃圾还田率下降的影响，居民及养殖区向环境排放的氮量并没有明显减少。受长江经济带城镇化进程加快以及农村人居环境整治的影响，通过污水直排的氮排放量呈现减少的趋势。无机氮肥施用、粪便和垃圾的产生、大气沉降、秸秆还田、污水直排和灌溉等氮流路径对氮径流流失的年均贡献比分别为0.53、0.28、0.11、0.04、0.02和0.01，随着时间的变化，各路径对氮流失量影响的趋势呈现差异，粪便和垃圾的产生对系统内氮流失的贡献比由1998年的0.33下降到2018年的0.26。从空间上看，四川省贯穿东北到西南的中部地区、浙江省中南部的大部分地区、重庆市东北和东南地区、云南省大部分地区都属于氮流失的高风险区，其分别占本省份面积的22.83%、22.10%、21.80%和25.14%，以上省份累积在土壤中的剩余氮素约有20%通过氮径流损失，极易造成水体的富营养化。

Spatial-temporal patterns and driving forces of nitrogen flows for agricultural plantation-consumption system in Yangtze River Economic Belt

To address the pollution caused by the excessive use of nitrogen(N)in agricultural and rural areas, this study used material flow analysis(MFA)and spatial analysis to depict the spatial and temporal evolution of N flows in the agricultural plantation-consumption system in the Yangtze River Economic Belt. The results showed that inorganic N fertilizer input was 1.088 5×10¹⁰ kg N in 1998, which increased at a rate of 1.14% until 2012 and then subsequently began to decrease. In 2018, the amount of inorganic N fertilizer applied was lower than that of 1998, but it remained the major source of N for the Yangtze River Economic Belt. The effective N output, in the form of crop production, was not affected by fluctuation of N input. The crop yield in 2018 was 18.97% and 25.71% higher than the yield in 1998 and 2008, respectively. In recent years, the quantity of breeding pigs in the Yangtze River Economic Belt has declined; however, the N emissions from residents and breeding areas have not reduced significantly. Owing to the acceleration of urbanization and the improvement of rural living environments, N emissions through directly discharged sewage in the rural area has decreased. The average annual percentage of N runoff losses from the pathways of inorganic N fertilizer application, feces and organic wastes production, atmospheric deposition, straw return to farmland, direct sewage discharge, and irrigation was 0.53, 0.28, 0.11, 0.04, 0.02, and 0.01, respectively. The influence of the different pathways varied over time; for instance, the contribution of feces and organic wastes production to N emissions dropped from 0.33 to 0.26 in 2018. Spatially, the high-risk areas of agricultural non-point source pollution are mainly distributed through the northeast to the southwest parts of Sichuan, the central and southern parts of Zhejiang, the northeast and southeast parts of Chongqing, and most parts of Yunnan, which account for 22.83%, 22.10%, 21.80%, and 25.14% of the province(city)area, respectively. In the above provinces, approximately 20% of the remaining N in the soil is lost through N runoff, which in turn leads to eutrophication of water bodies.