农业土地利用系统氮足迹与灰水足迹综合评价

氮足迹和灰水足迹作为定量分析人类活动对活性氮排放及水资源影响的指标,为农业土地利用系统环境效应评价提供了新的理论与途径。该文在氮足迹和灰水足迹理论的基础上,构建了县域尺度农业土地利用系统氮足迹与灰水足迹理论分析框架,以湖南桃江县为研究区,计算了农业土地利用系统氮足迹与灰水足迹。结果表明:1)1980-2010年氮足迹与灰水足迹、单位土地利用面积氮足迹与灰水足迹均呈逐年增加的趋势。2010年氮足迹和灰水足迹分别是1980年的2.02倍和2.36倍,单位土地利用面积氮足迹和灰水足迹分别是1980年的2.00倍和2.31倍;2)1980-2010年输入氮足迹和污染氮足迹分别增长了102.54%、128.79%。2010年肥料氮投入占输入氮足迹的72.72%,污染氮足迹占总氮足迹的32.79%;3)1980-2010年,每年氮肥灰水足迹均高于磷肥灰水足迹。活性氮流失的增长造成的稀释水量增加是农业土地利用系统灰水足迹增长的关键因素。评价结果显示,桃江县农业土地利用系统在足迹总量与单位土地利用足迹对大气和水资源的负面影响正在持续上升。氮足迹与灰水足迹综合评价方法能有效地识别区域农业土地利用过程对环境的负面效应,研究成果为降低农业土地利用过程的环境风险、制定农业土地利用系统优化方案提供参考。

Comprehensive evaluation for nitrogen footprint and gray water footprint of agricultural land use system

Abstract: Footprint research has gained more and more attention in ecology and sustainable development research fields. Nitrogen (N) footprint has theoretical and practical significance in evaluating the effect of activities on reactive N emission. Grey water footprint (GWF) is an indicator of aquatic pollution, which is important in the assessment of environmental effects of pollutants on water resource. In this paper, we employed both N footprint and GWF to evaluate environmental effects of agricultural land use system on reactive N loss and water quality. Based on the framework of the N footprint and the GWF, we built up an indicator system and assessed the environmental effects of agricultural land use system at the regional scale. To test the approach, the Taojiang County was chosen as the case study area. We assessed the N footprint and the GWF by using the official statistics during 1980 and 2010. The N footprints and the GWFs of the past agricultural land use system showed a large variation from 1980 to 2010 in Taojiang County: the total N footprint and the GWF increased drastically by 102.18% and 136.42% (i.e., from 15135.09 to 30599.40 t, and from 4.35×108 to 10.27×108 m3) respectively during the period of 1980-2010. The unit area N footprint and GWF were 0.35 t/hm2, 1.01×104 m3/hm2 in 1980 and increased to 0.70 t/hm2, 2.33×104 m3/hm2 in 2010. The input N footprint was increased from 15 084.23 t in 1980 to 30 551.39 t in 2010, while the unit area input N footprint were 0.35 t/hm2 in 1980 and then increased to 0.69 t/hm2 in 2010. The results indicated that the growth of fertilizer input was the main reason for N footprint increasing, which accounted for 72.72% of the input N footprint in 2010. Compared with 1980, the pollution N footprint gradually increased to 10 032.79 t in 2010. The proportion of pollution N footprint reached 32.84% in 2010. The unit area pollution N footprint was 0.10 t/hm2 in 1980 and increased to 0.23 t/hm2 in 2010. Based on the results, the GWF of N fertilizer was higher than that of phosphate fertilizer; and we selected the GWF of nitrogen fertilizer as the total GWF of agricultural land use system in Taojiang County. Compared with 1980, the total GWF of agricultural land use system in Taojiang County gradually increased to 10.27×108 m3 in 2010. The GWF of phosphate fertilizer increased from 1.88×108 to 5.92×108 m3 between 1980 and 2010. The unit area GWF of phosphate fertilizer was 0.44×104 m3/hm2 in 1980 and increased to 1.35×104 m3/hm2 in 2010. Increasing virtual water that was used to dilute the growing loss of reactive N was the key factor that had caused the increase of total GWF in Taojiang County. The result indicated that agricultural land use system had become the main contributor of air pollution and non-point source pollution, and this comprehensive approach in this paper could assess the environmental negative effects of agricultural land use system effectively. Based on the method, the negative effects of environmental issues on the N footprint, the GWF in county level were quantified preferably. The environmental sustainability of agricultural land use system was facing severe challenges in the increasing N footprint and the GWF of agricultural land use system in Taojiang County. The measures, including optimizing field management technique such as N fertilizer reduction, agricultural land use system designing, land use structure adjustment, are recommended for reducing the N footprint, the GWF and their environmental risk. The method proposed in this paper can provide a novel approach to quantify the losses of reactive N to the environment and to evaluate the environmental effects of agricultural land use system on water pollution level. The results can offer a valuable reference for the agricultural sustainable development and land use system optimal utilization for other similar grain producing regions.