Analysis of vulnerable level and characteristics of nitrogen losses from agricultural and livestock production system in Jing-Jin-Ji Region

To meet the increasing demand for food, agricultural and livestock production systems have been developed and intensified rapidly in recent years. Meanwhile, the separation of agricultural and livestock systems is becoming severe, leading to a higher risk of nitrogen loss (mainly from ammonia and nitrate) from agricultural and livestock systems, posing a significant threat to the ecological environment and human health. Accurate optimization and regulation of agricultural and livestock production systems are important pathways for achieving sustainable development of China’s agricultural and livestock production in the future, and this requires an accurate evaluation of the environmental risk threshold and delineation of vulnerable areas. Current evaluations of the environmental impacts of agricultural and livestock production systems in China usually focus only on a single accounting method and are restricted by crop nutrient demand, which lacks differentiated calculations for different agroecological zones. Beijing-Tianjin-Hebei (Jing-Jin-Ji) Region is an important region in China’s economy, culture and politics, with great potential for population and economic development, and its demand for agricultural and livestock products will further increase in the future. Therefore, this study divided the Jing-Jin-Ji Region into five agroecological zones: high-yield area in the piedmont plain, ecological conservation mountainous area, urban high-value agricultural area, middle- and low-yield area around Bohai Sea, and grassland pastoral area in Bashang. Based on a literature review, the thresholds for different forms of nitrogen loss were determined for different regions. Combined with the NUFER-county (NUtrient Flows in food chains, Environment, and Resource use at the county level) model, nitrogen losses from agriculture and livestock production systems in the Jing-Jin-Ji Region were estimated, and areas vulnerable to nitrogen losses were delineated in the region. The results of this study were as follows: The total nitrogen loss from agricultural and livestock production systems in Jing-Jin-Ji Region in 2017 was 1570.01 t, and the nitrogen loss per unit area was 221.64 kg·hm^–2. The risk of nitrogen loss in the study region was generally high, and the vulnerability risk levels varied across different regions. Nearly 99.37% and 93.09% of the entire region were identified as vulnerable area to ammonia emissions and nitrate losses, respectively. From a spatial distribution perspective, areas with severe nitrogen losses were high-yield area in the piedmont plain, ecological conservation mountainous area, and urban high-value agricultural area; different forms of nitrogen loss had similar spatial variation patterns. In addition, the risk of ammonia emission loss was relatively high, while the risk of nitrate loss was relatively low. Therefore, it is of great significance for the future green and sustainable development of agricultural and livestock production systems in the Jing-Jin-Ji agroecological zone to optimize the vulnerable areas of nitrogen losses through spatial planning and to actively promote precise management and regulation measures to reduce nitrogen losses in agricultural and livestock production systems.s.