Effluent entering streams also soils the atmosphere

The Corralles drainage ditch in Albuquerque, New Mexico, was one of 72 sites used to study nitrous oxide emissions from rivers and streams. Credit: Chelsea Crenshaw

The Corralles drainage ditch in Albuquerque, New Mexico, was one of 72 sites used to study nitrous oxide emissions from rivers and streams. Credit: Chelsea Crenshaw

Across the world, humans are causing rivers and streams to release the potent greenhouse gas nitrous oxide at levels three times higher than used in climate change predictions. Known as laughing gas when used as an anaesthetic, nitrous oxide is also a greenhouse gas over 300 times more powerful than CO2 on a per-molecule basis. How much of this gas comes from streams and rivers wasn’t previously well known, and scenarios predicting future climate change were based on estimates. Now, writing in the journal Proceedings of the National Academy of Sciences of the United States of America on Monday, a large team of US scientists has filled this knowledge gap.

Humans cause chemicals with high nitrogen contents from sources like fertilizers and sewage to enter water bodies as dissolved inorganic nitrogen (DIN). Microbes help break the DIN down, first by converting it into nitrates, and then converting these nitrate chemicals into nitrous oxide and nitrogen gas in a process called denitrification. Only a tiny amount of nitrous oxide is produced during denitrification in comparison to nitrogen gas. Previously, climate change models produced by the Intergovernmental Panel on Climate Change (IPCC) assumed that just 1 part of nitrous oxide is produced from 400 parts of DIN on average worldwide. Read the rest of this entry »