This process, due to the effects of climate change, is occurring in rivers much faster than in oceans and may lead to major problems for fish and other species living in the waterways.
This may lead to “acute death” in rivers across the southern United States, according to a new study in the journal Nature Climate Change, which studied the change in temperature and oxygen concentration in 800 rivers.
Animals that live in the water rely on dissolved oxygen to survive, absorbing the oxygen via gills or other means. If oxygen levels drop too low, this can cause mass die-offs of fish, which encourages the growth of decomposing bacteria, further sapping oxygen from the water and exacerbating the problem.
“This is a wake-up call,” said Li Li, co-author of the paper and professor of civil and environmental engineering at Penn State, said in a statement.
“We know that a warming climate has led to warming and oxygen loss in oceans, but did not expect this to happen in flowing, shallow rivers. This is the first study to take a comprehensive look at temperature change and deoxygenation rates in rivers — and what we found has significant implications for water quality and the health of aquatic ecosystems worldwide.”
The researchers studied 580 rivers in the U.S. and 216 rivers across Central Europe, finding that 87% of them had been getting progressively warmer over the past 40 years, while 70% of the rivers had been losing oxygen.
“Rivers are essential for the survival of many species, including our own, but they have historically been overlooked as a mechanism for understanding our changing climate,” said Li. “This is our first real look at how rivers throughout the world are faring — and it’s disturbing.”
Declining oxygen can also lead to increased amounts of greenhouse gases being released from the river and toxic metals being produced. The researchers’ model also showed that many species of fish could die out completely as a result of the oxygen loss and warming temperatures in the rivers over the next 70 years.