基于物质流模型的长三角城市群食物生产与消费系统氮素流动格局及影响因素

作为区域社会经济发展的重要增长极，城市群食物生产与消费系统活性氮的释放对区域氮素循环格局有着重要影响。采用物质流分析模型，定量分析2019年长三角城市群农田种植、畜禽养殖、水产养殖和人类消费子系统的氮素流动格局，评估各子系统氮素损失的结构，阐明氮素损失的空间分布，并探究氮素损失强度的主要影响因素。结果表明，系统总体氮输入为3 472.56 Gg/a，最大氮素输入项为化肥输入；系统总体氮输出为3 061.29 Gg/a，主要表现为氮素损失，占90.9%。农田种植、畜禽养殖和水产养殖子系统的氮素利用效率分别为42.6%、30.8%和40.1%。农田种植子系统对系统氮素损失的贡献最大，为1 325.53 Gg/a，占比为47.6%；其后依次为人类消费子系统、畜禽养殖子系统和水产养殖子系统。长三角各城市氮素损失强度空间异质性较大，上海、扬州、盐城较高，分别为26.43、23.20和22.26 kg/hm²；杭州、宣城、池州较低，分别为6.14、5.83和4.55 kg/hm²。氮素损失强度空间异质性与经济、人口、农业生产和土地利用等因素的相关性具有统计学意义（P<0.05或0.01），相关系数为0.42~0.76。

Nitrogen flow pattern and influencing factors of food production and consumption system in the Yangtze River Delta city cluster based on material flow model

As an important growth pole, the release of reactive nitrogen from food production and consumption system of city clusters greatly affects regional nitrogen cycle. The material flow analysis model was introduced to quantitatively analyze the nitrogen flow patterns among cropland, livestock, aquaculture and human consumption subsystems in the Yangtze River Delta city cluster in 2019. The structure of nitrogen loss to the environment from each subsystem, the spatial distribution of nitrogen loss, and the main influencing factors of nitrogen loss intensity were also investigated. The results indicated that the total nitrogen input to the food production and consumption system was 3 472.56 Gg/a. The largest component of the total nitrogen input came from fertilizer application. The total nitrogen output from the system was 3 061.29 Gg/a, mainly represented by nitrogen loss (90.9%). The nitrogen use efficiency (NUE) of cropland, livestock, and aquaculture subsystems was 42.6%, 30.8%, and 40.1%, respectively. Moreover, nitrogen loss from cropland subsystem was the highest, which was 1 325.53 Gg/a, accounting for 47.6% of the total nitrogen loss, followed by that from human consumption subsystem, livestock subsystem and aquaculture subsystem. The spatial heterogeneity of nitrogen loss intensity among cities in the Yangtze River Delta was significant. Shanghai, Yangzhou and Yancheng rank the top three in terms of nitrogen loss intensity, which was 26.43, 23.20 and 22.26 kg/hm2, respectively, while the nitrogen loss intensity of Hangzhou, Xuancheng and Chizhou was low, being 6.14, 5.83 and 4.55 kg/hm2, respectively. The result of Pearson correlation analysis showed that the spatial heterogeneity of nitrogen loss intensity was significantly correlated with factors including economy, population, agricultural production, and land use (P<0.05 or 0.01), with the correlation coefficients ranging from 0.42 to 0.76.