Normally discussions of climate change focus on carbon. Almost daily, new articles are posted on how human activity is altering carbon dioxide, or methane, levels in the atmosphere, and how this is potentially influencing climate around the world. But what about the other biogeochemical cycles? For a quick introduction to a problem with the nitrogen cycle, watch the GeoTimes video below:


Unfortunately, while the nitrogen cycle is often discussed in the classroom, it is rarely given as much attention as the carbon or water cycles. Some of this may be due to time constraints, but usually the lack of coverage seems to be linked to scarce coverage of nitrogen-related current events by the media. However, just last week an article was published in PLoS One   which provides an interesting twist of the potential consequences of human interference in the nitrogen cycle.

The articles subject is the potential toxic nature of nitrogen in aquatic ecosystems. Researchers at North Carolina State University, using the water flea Daphnia as a model organism, found that when exposed to nitrates and nitrites in the water, the metabolic pathways of the water flea convert these chemicals to nitric oxide. In living organisms, nitric oxide is an important chemical signal between cells. In humans, nitric oxide levels help regulate the activity of the gastrointestinal tract, respiration, and some aspects of brain activity (including those associated with learning and memory). The drug Viagra regulates nitric oxide levels in the penis, allowing for longer erections. Nitric oxide levels in the body are carefully regulated.  What was alarming from the NCSU study was the fact that Daphnia demonstrated developmental problems at nitrate concentrations that were well below those normally found in most water supplies. Now water fleas are not humans, the but question can now be raised as to whether the same effect is occurring in us, and at what concentrations do increased levels of nitrates and nitrites in our water supply produce toxic results.

Additional Resources

• PhysicalGeography.net ebook entry on the nitrogen cycle .
• McGraw-Hill Higher Education animation of the nitrogen cycle .
• PLoS article on aquatic nitrogen toxicology .