Urgent need for ammonia reduction: impact of emissions controls on atmospheric nitrogen inputs to Chinese river basins

Excess reactive nitrogen (i.e., ammonia and nitrogen oxides) from human activities deposited on the earth’s surface can increase the pollution of water. Aquatic ecosystems are affected by nitrogen deposition in two ways: direct deposition (when nitrogen deposits on surface water) and indirect deposition (when nitrogen deposits on land and then gets transported to water). ‘In China, the national government has implemented many emission control policies during the last few decades,’ explains first author Sijie Feng from WUR. ‘However, the effectiveness of these policies in reducing nitrogen deposition and its impact on water bodies from both direct and indirect ways remains unclear’. The research coupled a chemistry and transport model with a water quality model to bridge the existing gap.

Limited effectiveness of policies

The research revealed that over the past three decades, nitrogen deposition from human activities has either increased or decreased only slightly. This suggests that the effectiveness of Chinese emission control policies in reducing nitrogen deposition has been limited.

According to Feng, previous policies mostly focused on controlling acid gas emissions (i.e., nitrogen oxides and sulfur dioxide) from sources like power plant, industry, residential and transportation. However, there was a lack of specific policies to reduce agricultural ammonia emissions. The study indicated that in 2011, nitrogen deposition from agricultural sources (including fertilizer application and livestock breeding) accounted for about one-third of total nitrogen deposition in China. By 2019, agricultural contribution had further increased by 7%. As a result, total nitrogen deposition and its inputs to rivers increased in the 2010s. Especially, on average, 90% of the nitrogen deposition inputs to rivers were from indirect ways, which have often been overlooked in some studies.

Need to prioritize agricultural ammonia emission management

Feng: “Exploring synergistic agricultural measures involving water and air should be a priority, as this will help simultaneously reduce nitrogen deposition and water pollution”. The study indicated that in 2050, stricter standards on acid gas emissions are expected. This includes power plants, industry, residential, and transportation. Better management of agricultural ammonia is also expected. Mainly through intensified cultivation, grazing management enhancements, and the promotion of slow-release fertilizer. These measures are projected to decrease total nitrogen deposition by 56%. Also its inputs to rivers will decline by 47%, compared to 2019 levels.