Carbon dioxide is produced when any substance containing carbon is burned. It is also a product of breathing and of fermentation. There are different sources of the gas, including rivers and streams.
Given that running water emits carbon dioxide into the air, researchers are concerned that human activity could lead to an increase in the levels of the gas passed into the atmosphere via rivers and streams. This is not a straightforward task given the source of the gas in the water is not something that has been agreed between scientists.
One idea is that streams receive running water from fields, and the fields are a source of the carbon dioxide. The small streams then feed into rivers. A counter idea, and one that features in a new study, is that the source comes from organisms living in the running water and which are undergoing respiration. This is a reference to organisms at the microscopic level: bacteria and fungi.
The new research puts forward the notion that up to 30 percent of the carbon dioxide released from rivers and streams is from a microbial origin. This is based on a study that took account of a small creek and the mighty Mississippi River.
The key variation found was that the bigger a river becomes, the greater its contribution to atmospheric carbon dioxide, and the more organic matter in the river then the contribution becomes even greater still.
On this basis streams should not be considered passive conduits of carbon dioxide, collected from different areas along the way, but active generators of the gas based on the microbial life contained within them.
The research was conducted at Umeå University. The findings have been published in the journal Nature Geoscience, in a paper titled “Sources of and processes controlling CO2 emissions change with the size of streams and rivers.”
