Atmospheric Nitrogen Pollution Control Benefits the Coastal Environment

Area of Science:

• Environmental Science
• Oceanography
• Biogeochemistry

Background:

• Nitrogen is a critical limiting nutrient in marine ecosystems.
• Terrestrial nitrogen inputs to the ocean have increased significantly since preindustrial times.
• China is a major contributor to global nitrogen cycling, but pathways and sources of land-ocean transport are not well understood.

Purpose of the Study:

• To quantify nitrogen transfer from China to the ocean.
• To identify major sources and pathways of nitrogen transport.
• To evaluate potential mitigation strategies for reducing ocean nitrogen pollution.

Main Methods:

• Integrated modeling approach combining CHANS, WRF-Chem, and WNF models.
• Estimation of nitrogen transfer to the ocean in 2017.
• Analysis of atmospheric deposition's impact on offshore chlorophyll concentration.
• Identification of key contributing sectors and regions.

Main Results:

• Estimated 8 million tonnes (Tg) of nitrogen transferred to the ocean from China in 2017.
• Atmospheric deposition accounted for one-third of the total nitrogen input and explained about half of the variation in offshore chlorophyll concentration.
• The Bohai Sea exhibited the highest nitrogen input (214 kg N ha⁻¹), significantly exceeding other areas.
• Agricultural systems (55%) and domestic sewage (21%) were the largest contributors to nitrogen export.

Conclusions:

• Mitigation measures can reduce nitrogen export to the ocean by 43%.
• Addressing air pollution by reducing ammonia and nitrogen oxide emissions is crucial for ocean protection, contributing 33% to the potential reduction.
• Prioritizing nitrogen reduction in agricultural and transport sectors offers the most cost-effective benefits for the marine environment.