Atmospheric nitrogen deposition in the Yangtze River basin: Spatial pattern and source attribution

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Ecosystem Ecology

Background:

• The Yangtze River basin is a global hotspot for nitrogen (N) deposition.
• Riverine N output from this region significantly impacts China's aquatic ecosystems.
• Understanding N deposition patterns is crucial for environmental management.

Purpose of the Study:

• To construct a basin-scale map of total dissolved inorganic nitrogen (DIN) deposition.
• To assess the contributions of various reactive nitrogen (N_r) emission sectors to DIN deposition.
• To evaluate N deposition levels against critical loads for ecosystems.

Main Methods:

• Compiled published data from 100 observational sites (2000-2014) for basin-scale deposition patterns.
• Utilized the GEOS-Chem model to attribute DIN deposition to different N_r emission sources.
• Compared modeled DIN deposition with established critical load values for ecosystems.

Main Results:

• Significant spatial variation in total DIN deposition (average 33.2 kg N ha^-1 yr^-1) was observed, with hotspots in the central basin.
• Approximately 82% of the basin area exceeded the critical N deposition load for semi-natural ecosystems.
• Fertilizer use (40%) was identified as the dominant source of DIN deposition, followed by livestock (11%), industry (13%), power plants (9%), and transportation (9%).

Conclusions:

• Mitigation strategies for N deposition must be localized, focusing on hotspots and considering regional emission sources.
• Reducing ammonia (NH₃) emissions from improper fertilizer application is a priority for curbing N deposition.
• Integrated control measures addressing fertilizer use and other major regional emission sectors are necessary for effective N management.