Oxygen levels are dropping in lakes across the United States and Europe, which could threaten large numbers of freshwater fish populations and lead to an increase in algae blooms and methane emissions, a recent study concluded.
A group of researchers studied the temperatures and amount of oxygen in the water in nearly 400 lakes between 1941 and 2017. Their research, published Wednesday in the journal Nature, found that oxygen levels had declined 5.5% in surface waters of the observed lakes and 18.6% in deep waters.
The study’s authors said their findings suggest warming temperatures and decreased water clarity from human activity were contributing to the decline in oxygen levels.
A Nature paper reports widespread long-term declines in temperate lake oxygen levels. The trend may be linked to warming temperatures and decreasing water clarity. The declines could threaten essential lake ecosystems. https://t.co/uCjjp2CmJY pic.twitter.com/2ZIIoz1i5Q
— nature (@Nature) June 2, 2021
Craig Williamson, a biology professor at Miami University in Ohio and co-author of the study, told The Associated Press that oxygen “is one of the best indicators of ecosystem health” and the changes in oxygen levels observed in the study “reflect a pronounced human footprint.” (RELATED: Humans Making So Much Noise On The Oceans That Fish Can’t Hear Each Other)
The oxygen decline in lakes threatens to kill off a massive number of freshwater fish populations. Nearly half of all fish species live in freshwater and there are at least 800 freshwater fish species in North America alone, according to National Geographic.
The significant drop in deep water oxygen levels observed in the study is especially a threat to species that are more sensitive to higher temperatures, such as cold water fish, because they depend on cooler temperatures found deeper in the water. But those species can’t survive if deep waters continue to lose oxygen, the AP noted.
Kevin Rose, a biology professor at Rensselaer Polytechnic Institute and co-author of the study, told the AP that changes in oxygen levels “are the conditions that sometimes lead to fish kills in water bodies.” He added that deep water oxygen decline “means that a lot of habitats for cold water fish could become inhospitable.”