Reducing nitrogen availability in our nitrogen-rich world

Calculation of this deficit in climate change models is critical to obtaining an accurate estimate of carbon sequestration capacity.

Since the mid-20th century, research and debate have focused on the detrimental effects of excess nitrogen on terrestrial and aquatic ecosystems. However, new evidence suggests that the world is now undergoing a double trajectory in the presence of nitrogen. 

First, after years of paying attention to excess nitrogen in the environment, our growing understanding has raised new concerns about nitrogen deficiency in areas that do not receive significant amounts of nitrogen from human activities. In a recent review article, Evidence, Causes and Consequences of Nitrogen Depletion in Terrestrial Ecosystems, in the journal Science, a cross-institutional research team describes the causes of nitrogen depletion and how it affects ecosystem function.

"There's too much nitrogen and too little nitrogen on Earth," said Rachel Mason, lead author and former postdoctoral researcher at the National Center for Socio-Environmental Synthesis.

Over the last century, humans have doubled their global supply of reactive nitrogen through industrial and agricultural activities. This nitrogen accumulates in rivers, inland lakes, and coastal waters, sometimes causing eutrophication, dead zones with low oxygen levels, and harmful algae growth. 

This negative effect of excess nitrogen has prompted scientists to study nitrogen as a pollutant. However, increasing carbon dioxide and other global changes have increased the demand for nitrogen by plants and microbes. Recently published research papers suggest that nitrogen availability decreases in many regions of the world, with important implications for plant growth.

"These findings show how the world is changing in complex and surprising ways," said Peter Groffman, co-author and professor in the Center for Advanced Research of the CUNY Graduate Center's Environmental Science Initiative. "Our results demonstrate the importance of having long-term data and targeted synthesis efforts to understand these changes and their impact on ecosystems and human health and well-being.

Researchers reviewed long-term global and regional studies and found evidence of reduced nitrogen availability caused by various environmental changes, one of which increases atmospheric carbon dioxide levels.