常熟市食物链系统氮素生产-消费平衡及环境负荷特征

Characteristics of production-consumption balance and environmental loads of nitrogen in food chain system in Changshu City

为了解常熟市食物链系统氮素流动特征,通过构建食物链氮素流动模型,应用模型计算该市2000—2013年农田生产、畜禽养殖、家庭消费三个子系统氮素流动通量,对食品氮的生产消费平衡和氮素环境损失及负荷特征进行了分析。结果表明：2000—2013年常熟市植物性食品氮每年盈余,年均盈余量2 171.54 t;动物性食品氮在2000—2002年盈余47.71~56.92 t,2003—2013年动物性食品氮生产少于需求,年均亏缺210.03 t;该市食物链系统年均损失氮素2.34万t,三子系统氮素年均环境损失率分别为65.39%、69.03%、68.16%;氮素损失平均每年给当地环境造成1.81万t氮负荷,分别有40.33%、29.65%、30.02%进入水体、大气、土壤环境。可见,常熟市食物链氮素流动系统中存在氮素环境损失率高、环境负荷量大的问题。对此,可采取提高废弃物氮的循环利用率,减少农畜食品生产中氮素投入量的措施进行调控管理。

Changshu is a developed city in the Taihu Lake Region with intensive agriculture and dense population. It was reported that nitrogen was primary pollutant of the surface water in Changshu City. To understand the characteristics of nitrogen flows in Changshu food chain system, a nitrogen flow model in food chain system was constructed. The model was then applied to calculate the nitrogen fluxes in crop production subsystem, livestock breeding subsystem and household consumption subsystem of Changshu City from 2000 to 2013. The characteristics of production and consumption balance and environmental loads of nitrogen were finally analyzed. Results showed that plantderived food nitrogen had an average annual surplus of 2 171.54 t·a-1from 2000 to 2013. Animal-derived food nitrogen showed a little surplus of 47.71~56.92 t from 2000 to 2002. From 2003 to 2013, however, animal-derived food nitrogen was short of 210.03 t·a-1. The food chain system lost 23 382.70 t N·a-1into the environment. The loss rates of three subsystems were 65.39%, 69.03% and 68.16% for crop production, livestock breeding and household consumption subsystems, respectively. The lost nitrogen caused an environmental load of18 101.95 t N·a-1, 40.33% of which was transported into water, 29.65% into atmosphere and 30.02% into soil. This revealed that the nitrogen loss rates were relatively high and the environmental load of nitrogen was huge in the food chain system in Changshu City. Enhancing nitrogen cycle utilization efficiency and decreasing nitrogen inputs in farm-livestock production would be critical to nitrogen control in agricultural system.