Ministry of Education Key Laboratory for Earth System Modeling, Department of Earth System Science, Tsinghua University, Beijing, China.
AI for Earth Laboratory, Cross-strait Tsinghua Research Institute, Xiamen, China.
Nature. 2019 Mar;567(7749):516-520. doi: 10.1038/s41586-019-1001-1. Epub 2019 Feb 28.
The nitrogen cycle has been radically changed by human activities. China consumes nearly one third of the world's nitrogen fertilizers. The excessive application of fertilizers and increased nitrogen discharge from livestock, domestic and industrial sources have resulted in pervasive water pollution. Quantifying a nitrogen 'boundary' in heterogeneous environments is important for the effective management of local water quality. Here we use a combination of water-quality observations and simulated nitrogen discharge from agricultural and other sources to estimate spatial patterns of nitrogen discharge into water bodies across China from 1955 to 2014. We find that the critical surface-water quality standard (1.0 milligrams of nitrogen per litre) was being exceeded in most provinces by the mid-1980s, and that current rates of anthropogenic nitrogen discharge (14.5 ± 3.1 megatonnes of nitrogen per year) to fresh water are about 2.7 times the estimated 'safe' nitrogen discharge threshold (5.2 ± 0.7 megatonnes of nitrogen per year). Current efforts to reduce pollution through wastewater treatment and by improving cropland nitrogen management can partially remedy this situation. Domestic wastewater treatment has helped to reduce net discharge by 0.7 ± 0.1 megatonnes in 2014, but at high monetary and energy costs. Improved cropland nitrogen management could remove another 2.3 ± 0.3 megatonnes of nitrogen per year-about 25 per cent of the excess discharge to fresh water. Successfully restoring a clean water environment in China will further require transformational changes to boost the national nutrient recycling rate from its current average of 36 per cent to about 87 per cent, which is a level typical of traditional Chinese agriculture. Although ambitious, such a high level of nitrogen recycling is technologically achievable at an estimated capital cost of approximately 100 billion US dollars and operating costs of 18-29 billion US dollars per year, and could provide co-benefits such as recycled wastewater for crop irrigation and improved environmental quality and ecosystem services.
人类活动极大地改变了氮循环。中国消耗了全球近三分之一的化肥。化肥的过度使用以及来自畜牧业、城市和工业的氮排放量增加，导致了普遍的水污染。在异质环境中量化氮的“边界”对于有效管理当地水质非常重要。在这里，我们结合水质观测和农业及其他来源的氮排放量模拟，估算了 1955 年至 2014 年期间中国水体氮排放量的空间分布。我们发现，到 20 世纪 80 年代中期，大多数省份的地表水质量标准（每升 1 毫克氮）就已经超标，而目前人为向淡水中排放的氮（每年 1450 万吨氮±310 万吨氮）约为估计的“安全”氮排放阈值（每年 520 万吨氮±70 万吨氮）的 2.7 倍。目前通过污水处理和改善农田氮管理来减少污染的努力可以部分缓解这种情况。生活污水处理有助于在 2014 年将净排放量减少 0.7±0.1 百万吨，但代价是高昂的货币和能源成本。改进农田氮管理每年可以再减少 230 万吨氮左右，约占向淡水过度排放的 25%。要想成功恢复中国清洁的水生态环境，还需要进行变革性的改变，将全国养分循环利用率从目前的平均 36%提高到 87%左右，这一水平与中国传统农业的水平相当。尽管这一目标雄心勃勃，但在估计的 1000 亿美元资本成本和每年 180 亿至 290 亿美元的运营成本下，实现如此高的氮循环利用率在技术上是可行的，同时还可以带来循环利用废水进行农作物灌溉以及改善环境质量和生态系统服务等好处。
