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03-06-2024

River respiration is a lot like breathing in humans

Have you ever thought of rivers as being living things? They gurgle, flow, and teem with life, but did you know they also “breathe”? Scientists at the Pacific Northwest National Laboratory (PNNL) are delving into the process of river respiration. 

Surprisingly, just like we take in oxygen and release carbon dioxide, rivers do the same through tiny organisms and organic matter.

Respiration process in rivers

Rivers “breathe” through a complex series of chemical reactions carried out by tiny organisms like bacteria and algae. They absorb dissolved oxygen from the water, similar to how we breathe air. 

The oxygen fuels a process called decomposition, where they break down dead plants, algae, and animal waste in the river. This breakdown releases energy, which these organisms need to survive and grow, just like we get energy from food. 

Rivers also release carbon dioxide back into the water, like humans do when we exhale. Importantly, this process releases essential nutrients – like nitrogen and phosphorus –  that are vital for the growth of other organisms in the river. 

The entire cycle, from oxygen absorption to nutrient release, is essential for maintaining healthy oxygen levels in the river and supporting a diverse range of life underwater.

Organic matter as fuel

As previously mentioned, rivers contain tiny pieces of dead plants and animals, which is called organic matter. This organic matter acts as food for organisms in the water and helps keep the water clean and healthy. 

The type of organic matter present depends on various factors like how the land around the river is used, if there is any pollution, and if there have been any disturbances in the environment, both natural and human-caused. 

Interestingly, the speed of breakdown depends on the type of matter. Some things, like wood and leaves, take longer to “digest.” Knowing how fast things break down is important for keeping rivers healthy and usable.

Where does river respiration occur?

The location of the respiration can vary greatly. For instance, in the wide Columbia River, most of the river’s respiration happens in the water itself. The vast amount of water provides a large space for this process to take place. 

In smaller streams, however, the bottom sediment becomes the key location for microbial respiration. This is because the sediment is in direct contact with organic matter that sinks to the bottom, providing a rich food source for microbes

Fluctuations in river respiration 

The size of the sediment particles also plays a role in how quickly respiration occurs. Larger rocks in the sediment create more space and surfaces for microbes to live and work on, potentially making respiration more efficient. The increased activity not only helps break down organic matter but also helps the river clean itself by breaking down pollutants.

Therefore, where and how much respiration happens in a river system is constantly changing and depends on both the physical features of the river, like the amount of water and the size of the sediment particles, and where organic matter is located. 

Water quality management 

The research on the breakdown of organic matter in rivers has important implications for several areas. For example, it can help improve water quality management. 

By understanding what factors influence how quickly organic matter decomposes, scientists and policymakers can develop better strategies for cleaning up rivers. They can identify the pollutants that break down the slowest and focus on removing those first.

River conservation 

Moreover, the study can inform conservation efforts. If we know how rivers function, we can take better care of them. Healthy rivers provide clean water, habitat for fish and other wildlife, and help regulate nutrients. 

“Understanding what principles regulate processes and how they work across systems is a key goal of our work,” explained PNNL Earth scientist Allison Myers-Pigg.

“This knowledge provides a foundation for building models that can predict the future health of streams and rivers, including how they might be impacted by big disturbances. Without this knowledge, we cannot make accurate predictions.” 

The study is published in the journal Frontiers in Water.

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