Keeping Nitrogen Use in China within the Planetary Boundary Using a Spatially Explicit Approach

Area of Science:

• Environmental Science
• Agricultural Science
• Water Resource Management

Background:

• Nitrogen (N) is crucial for food production but excess N leads to significant water pollution.
• Current understanding of N boundaries for water quality is limited, with a focus on regional reduction targets.
• Complex relationships between N inputs and in-stream N concentrations necessitate a refined approach.

Purpose of the Study:

• To derive a spatially explicit boundary for N inputs to rivers to protect surface water quality in China.
• To explore strategies for meeting these N boundaries while balancing impacts on water quality and food production.
• To provide insights for developing region-specific policies for water quality improvement.

Main Methods:

• Utilized a modified multiscale nutrient modeling system to simulate N inputs.
• Developed a bottom-up approach to establish spatially explicit N input boundaries for rivers.
• Compared "water quality first" and "food production first" scenarios to assess trade-offs.

Main Results:

• Simulated approximately 6.5 Tg of N inputs allowed for China in 2012, with variable limits based on region (higher for intensive agriculture, lower for urban areas).
• Reducing fertilizer and manure use could enable 45-76% of streams to meet N water quality thresholds under various scenarios.
• Trade-offs between water quality and food production were identified in 2-8% of streams, potentially impacting 7-28% of crop production.

Conclusions:

• Spatially explicit N input boundaries are essential for managing water quality and food production.
• Policy decisions involve trade-offs, requiring careful consideration of regional impacts.
• The findings support the development of targeted policies to enhance water quality in China.