A new study has uncovered that the Erhai Lake Basin in southwest China is releasing far more atmospheric nitrogen pollution than it absorbs, raising concerns about regional air quality, ecosystem health, and long-distance pollution transport.
Atmospheric reactive nitrogen is a group of nitrogen compounds that influence air pollution, climate, and ecosystem stability. These compounds play important roles in forming fine particulate matter, worsening smog, and driving water eutrophication that threatens biodiversity and drinking water safety. Understanding where these pollutants originate and how they move through the environment is essential for designing effective pollution control strategies.
In the new research, scientists conducted one of the most comprehensive analyses to date of the atmospheric nitrogen budget in the Erhai Lake Basin, a subtropical plateau lake ecosystem widely recognized for its ecological sensitivity and importance to regional tourism and agriculture. By combining emission inventories with field monitoring across multiple sites, the researchers mapped both nitrogen emissions and atmospheric deposition across the entire watershed.
The team estimated that total atmospheric reactive nitrogen emissions in the basin reached more than 10,700 metric tons per year, while deposition returned only a small fraction of that nitrogen back to land and water surfaces. The imbalance created a net surplus of over 8,200 metric tons annually, clearly identifying the basin as a major source of atmospheric nitrogen pollution.
"Our findings reveal that the Erhai Lake Basin functions as a strong atmospheric nitrogen exporter rather than a pollution sink," said the study's corresponding author. "This imbalance means that nitrogen emitted locally can travel far beyond the basin, affecting air quality and ecosystems in surrounding regions."
Agricultural activities were identified as the dominant contributor to ammonia emissions, accounting for more than 90 percent of ammonia-related nitrogen pollution. Livestock farming and fertilizer use contributed nearly equal shares of these emissions. Meanwhile, transportation sources such as trucks and passenger vehicles were responsible for almost all nitrogen oxide emissions, highlighting the growing role of traffic pollution in rapidly developing rural and tourist regions.
Although nitrogen emissions were high, the study found that atmospheric deposition levels in the basin were relatively moderate compared with heavily industrialized regions of China. However, atmospheric nitrogen still represented a significant contributor to nutrient loading in Erhai Lake, potentially accelerating harmful algal blooms and water quality degradation.
"Our results demonstrate that even moderate atmospheric deposition can significantly impact lake ecosystems," the authors noted. "This is especially critical for plateau lakes like Erhai that are highly sensitive to nutrient enrichment."
The researchers also identified unique geographical features that may intensify the environmental impact of nitrogen pollution. The basin's mountain-valley terrain creates local wind circulation patterns that can trap pollutants and enhance their atmospheric lifetime. This mechanism increases the likelihood that nitrogen compounds will be transported over long distances, potentially contributing to regional haze and secondary particulate pollution.
The study emphasizes the urgent need for coordinated pollution control strategies targeting both agricultural and transportation sectors. Improved manure management, precision fertilizer application, and cleaner vehicle technologies were identified as key steps for reducing nitrogen emissions.
Beyond immediate policy implications, the research provides a valuable framework for evaluating atmospheric nitrogen cycling in other vulnerable lake ecosystems worldwide. The authors suggest that future work should focus on improving local emission data, expanding nitrogen monitoring systems, and using atmospheric modeling to track pollution transport pathways.
"Quantifying nitrogen budgets allows us to understand how human activities reshape environmental nutrient cycles," the researchers explained. "Only by addressing multiple emission sources simultaneously can we effectively reduce nitrogen pollution and protect fragile freshwater ecosystems."
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Journal Reference: Shen Q, Tang B, Wu X, Kang J, Li J, et al. 2026. A large net source revealed by the atmospheric reactive nitrogen budget in a subtropical plateau lake basin, southwest China. Nitrogen Cycling 2: e006 doi: 10.48130/nc-0025-0018
https://www.maxapress.com/article/doi/10.48130/nc-0025-0018
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