GEOGRAPHY

Reducing “fertilizer” in agriculture helps reduce ammonia nitrogen deposition in sea areas


Recently, the team of Liu Lei, a researcher at the College of Resources and Environment of Lanzhou University, cooperated with Liu Xuejun, a professor at China Agricultural University, and published results in the Proceedings of the National Academy of Sciences in the United States entitled “Assessment of Global Marine Nitrogen Deposition and Mitigation Potential for Reducing Agricultural Fertilizer Overuse”, through multidisciplinary cross-cooperation in geography, atmospheric science, agricultural science, ecology and other disciplines, to explore the temporal and spatial patterns and changes of nitrogen deposition in marine areas.

Schematic diagram of agricultural nitrogen emissions entering marine systems through atmospheric circulation. Photo courtesy of the research group

Nitrogen is important for the material cycle of marine ecosystems. Global population growth and rising consumption levels are putting enormous pressure on agri-food production, but agri-food production (cropping and livestock) produces large amounts of ammonia emissions, which settle offshore waters under the influence of atmospheric circulation, resulting in eutrophication of marine water bodies, reducing water quality, oxygen loss and harmful algae growth. Many land-based discharge areas are close to the coast, but the spatial and temporal situation of how ammonia emissions from agri-food production processes affect nitrogen deposition in marine areas remains unclear.

Global cereal and meat production more than doubled and more than tripled between 1970 and 2018, respectively, and ammonia emissions from agricultural production account for an increasing share of total reactive nitrogen emissions, increasing from 35% in 1970 to 53% in 2018. Due to the lack of effective control of ammonia emissions from the food system, the global ammonia nitrogen emission ratio is changing rapidly, from 0.73 to 1.22 between 1970 and 2018, and global ammonia emissions dominated by agriculture exceed industry-led nitrogen oxide emissions. Farming and livestock are the two main areas of increase in global ammonia emissions, with ammonia emissions from livestock increasing by 69% between 1970 and 2018 and ammonia emissions from farmland more than fourfold.

The research team established an analysis framework for ammonia emissions from agricultural systems into marine systems through atmospheric circulation, constructed long-time (1970-2018) ammonia emissions and marine nitrogen deposition datasets, and systematically evaluated the impact of ammonia emissions from agricultural production processes on the spatial and temporal situation of nitrogen deposition in marine areas.

According to the Atmospheric Chemical Transport Model (GEOS-Chem) simulation, about 30-38% of global terrestrial nitrogen emissions settle in marine systems and the rest in terrestrial systems. Global ocean ammonia nitrogen deposition increased by 89% from 1970 to 2018, with the highest ammonia deposition off the coast of China and India in 2018, followed by the eastern coast of Brazil, the Black Sea and the eastern coast of the United States (Northwest Atlantic shelf). Ammonia nitrogen deposition in eastern China and eastern India increased by 2.2 times and 1.9 times respectively from 1970 to 2018; ammonia nitrogen deposition in the eastern waters of the United States and the coast of Western Europe remained at a low level from 1970 to 2018, about 1/5 of ammonia nitrogen deposition in eastern China and eastern India.

Due to the successful control of nitrogen oxide emissions in the EU and the United States, nitrate deposition in the western waters of Europe (Northeast Atlantic continental shelf) and the eastern coast of the United States (Northwest Atlantic continental shelf) decreased significantly between 2000 and 2018, falling by 35% and 42%, respectively. Nitrate deposition in China’s eastern waters decreased by 15% from 2010 to 2018. Nitrate subsidence in global seas fell by 6% from 2010 to 2018.

Global agricultural production ammonia emissions account for 94% of ammonia nitrogen deposition in sea areas, and agricultural ammonia deposition accounts for more than 90% of ammonia deposition in most sea areas. Given the rapid increase in ammonia nitrogen deposition in the global sea, there is an urgent need to reduce the overuse of agricultural fertilizers. It is estimated that the amount of nitrogen fertilizer can be reduced by 38% without affecting the current yield. If the overuse of nitrogen fertilizers can be avoided, ammonia nitrogen deposition in the global ocean will be reduced by 15%, ammonia nitrogen deposition off the eastern coast of China and India will be reduced by 21-25%, and the western waters of Europe (Northeast Atlantic continental shelf) and the eastern waters of the United States (Northwest Atlantic continental shelf) will be reduced by 12-17%. For different regions, the overuse of nitrogen fertilizers varies from crop to crop. In the agricultural region of the Mideastern United States, excessive application of corn nitrogen fertilizer is quite common, and nitrogen overdose can exceed 50 kg N ha-1yr-1. In China and India, rice planting nitrogen excess is a serious problem, followed by wheat and maize, and in some areas nitrogen excess can exceed 100 kg N ha-1yr-1. (Source: China Science News, Wen Caifei, Faisha)

Related paper information:https://doi.org/10.1073/pnas.2221459120



Source link

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button