Study: Hundreds of Lakes in US, Europe Lose Oxygen
2021-06-10
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1Researchers say oxygen levels have dropped in hundreds of lakes across the United States and Europe over the last 40 years.
2A new study suggests the oxygen loss can lead to more fish dying and increased algae growth.
3Scientists examined the temperature and the amount of dissolved oxygen in nearly 400 lakes.
4Dissolved oxygen is the amount of oxygen gas contained in water.
5They discovered widespread drops in oxygen levels.
6The study recently appeared in the publication Nature.
7It found that dissolved oxygen decreased an average of 5.5 percent in the surface water of the lakes and 18.6 percent in the deep water.
8The researchers say their findings suggest that warming temperatures and decreased water clarity from human activity are causing oxygen levels to fall.
9Craig E. Williamson is a biology professor at Miami University in the state of Ohio and a co-writer of the study.
10He told The Associated Press that testing for oxygen is one of the best ways to judge how healthy water systems are.
11The study's findings suggest "a pronounced human footprint," he said.
12That footprint includes warming caused by climate change, the researchers said.
13In addition, decreased water clarity can be caused by runoff from human waste systems, fertilizers, cars and power plants.
14Losses in dissolved oxygen in Earth's water systems have been reported before.
15A 2017 study of oxygen levels in the world's oceans showed a two percent drop since 1960.
16But less was known about lakes, which lost two to nine times as much oxygen as oceans, the study found.
17In the past, other researchers had reported oxygen decreases in individual lakes over a long period of time.
18But those studies did not examine as many lakes around the world, said Samuel B. Fey.
19He is a biology professor at Oregon's Reed College who studies lakes.
20He was not involved in the latest study.
21Fey said an important finding was that the researchers were able to show such a notable drop in dissolved oxygen levels.
22Also, the drops were found at both the surface and in deep parts of the lakes.
23The deep water drop in oxygen levels may affect organisms that are more sensitive to temperature increases, such as cold water fish.
24During the summer months, they depend on cooler temperatures found in deeper water.
25But if deep waters are low in oxygen, the organisms struggle to survive.
26"Those are the conditions that sometimes lead to fish kills in water bodies," study co-writer Kevin C. Rose said.
27This means that a lot of areas cold water fish depend on "could become inhospitable," he added.
28Other organisms, Rose said, do better in warmer temperatures at the surface level and can get enough oxygen by remaining there.
29About one fourth of the lakes studied showed increasing oxygen in surface waters.
30Rose said this is a bad sign because it points to increased algal blooms - the sudden growth of algae.
31In those lakes, dissolved oxygen was "very low" in deep waters, likely creating unlivable conditions for many species, the researchers said.
32I'm Bryan Lynn.
1Researchers say oxygen levels have dropped in hundreds of lakes across the United States and Europe over the last 40 years. 2A new study suggests the oxygen loss can lead to more fish dying and increased algae growth. 3Scientists examined the temperature and the amount of dissolved oxygen in nearly 400 lakes. Dissolved oxygen is the amount of oxygen gas contained in water. They discovered widespread drops in oxygen levels. 4The study recently appeared in the publication Nature. It found that dissolved oxygen decreased an average of 5.5 percent in the surface water of the lakes and 18.6 percent in the deep water. 5The researchers say their findings suggest that warming temperatures and decreased water clarity from human activity are causing oxygen levels to fall. 6Craig E. Williamson is a biology professor at Miami University in the state of Ohio and a co-writer of the study. He told The Associated Press that testing for oxygen is one of the best ways to judge how healthy water systems are. The study's findings suggest "a pronounced human footprint," he said. 7That footprint includes warming caused by climate change, the researchers said. In addition, decreased water clarity can be caused by runoff from human waste systems, fertilizers, cars and power plants. 8Losses in dissolved oxygen in Earth's water systems have been reported before. A 2017 study of oxygen levels in the world's oceans showed a two percent drop since 1960. But less was known about lakes, which lost two to nine times as much oxygen as oceans, the study found. 9In the past, other researchers had reported oxygen decreases in individual lakes over a long period of time. But those studies did not examine as many lakes around the world, said Samuel B. Fey. He is a biology professor at Oregon's Reed College who studies lakes. He was not involved in the latest study. 10Fey said an important finding was that the researchers were able to show such a notable drop in dissolved oxygen levels. Also, the drops were found at both the surface and in deep parts of the lakes. 11The deep water drop in oxygen levels may affect organisms that are more sensitive to temperature increases, such as cold water fish. During the summer months, they depend on cooler temperatures found in deeper water. But if deep waters are low in oxygen, the organisms struggle to survive. 12"Those are the conditions that sometimes lead to fish kills in water bodies," study co-writer Kevin C. Rose said. This means that a lot of areas cold water fish depend on "could become inhospitable," he added. 13Other organisms, Rose said, do better in warmer temperatures at the surface level and can get enough oxygen by remaining there. 14About one fourth of the lakes studied showed increasing oxygen in surface waters. Rose said this is a bad sign because it points to increased algal blooms - the sudden growth of algae. In those lakes, dissolved oxygen was "very low" in deep waters, likely creating unlivable conditions for many species, the researchers said. 15I'm Bryan Lynn. 16The Associated Press reported on this story. Bryan Lynn adapted the report for VOA Learning English. Mario Ritter, Jr. was the editor. 17We want to hear from you. Write to us in the Comments section, and visit our Facebook page. 18__________________________________________________________ 19Words in This Story 20algae - n. a plant with no stem or leaves that grows in or near water 21pronounced - adj. very easy to notice 22fertilizer - n. a substance or a special chemical that is added to soil to help the growth of plants 23inhospitable - adj. not pleasant or easy to live in 24bloom - n. a fast and excessive growth of water organisms 25species - n. biology : a group of animals or plants that are similar and can produce young animals or plants : a group of related animals or plants that is smaller than a genus