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Temperature is the main driver of oxygen in U.S. rivers

The quantity of dissolved oxygen in rivers is highly important for the survival of the plants and animals inhabiting them. However, the oxygen concentration varies substantially among rivers, depending on their temperature, light, and flow.

To clarify which of these factors has the largest impact on the concentration of dissolved oxygen, a team of scientists led by Pennsylvania State University used a deep learning model to analyze data from hundreds of rivers across the United States, and found that temperature is the most significant factor driving oxygen concentrations. 

The amount of oxygen dissolved in rivers is a critical measure of water quality since fish and other aquatic organisms rely on it to breathe.

“Studies have shown that three major factors — flow, temperature, and sunlight — influence the amount of dissolved oxygen found in a river or stream. We wanted to know, at the U.S. continental scale, which of these competing drivers was dominant,” said lead author Wei Zhi, an assistant professor of Civil and Environmental Engineering at Penn State. 

Previous studies have argued that all the three factors are equally important, since how quickly a river flows impacts how fast atmospheric oxygen can dissolve in water, the level of sunlight shining into the water affects how much oxygen aquatic plants can produce on their own, and temperature affects how much oxygen the water can pull from air.

However, since there has been little consistency in how dissolved oxygen concentrations have been measured in different rivers, the Penn State team used 40 years of data from 580 rivers across the country to train a deep learning model that could clarify the relationship between weather conditions and dissolved oxygen.

“Traditionally, it has been very difficult to predict the dissolved oxygen levels on such a large scale, simultaneously with one model. But with a deep learning and big data approach, we can do that. Deep learning models enable large-scale systematic analysis of patterns and drivers,” explained senior author Li Li, a professor of Civil and Environmental Engineering at Penn State.

The analysis reveled that, at a continental scale, temperature significantly outweighed both light and stream flow in affecting the dissolved oxygen concentrations. While light was the second-important factor, stream flow appeared to have minimal influence.

“Temperature is the predominant driver of daily dissolved oxygen dynamics in U.S. rivers. Fairly accurate predictions of oxygen concentration can be made by temperature alone. Dissolved oxygen is declining in warming rivers, which has important implications for water security and ecosystem health in the future warming climate,” Zhi concluded.

The study is published in the journal Nature Water.

By Andrei Ionescu, Staff Writer

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