Lakes are losing oxygen-their inhabitants are in danger


Ross also found a second problem: due to a series of factors such as erosion, algae growth, and loss of fertilizer from nearby farmland and residential developments, deep water has become increasingly unclear. Turbid water makes plants less likely to survive, which means there is less photosynthesis and oxygen below. Of course, this is bad news for the creatures in the lake. “Just like humans, every complex life form on Earth depends on oxygen,” Ross said. “In water, it is in dissolved form.”

Each species has a unique critical oxygen threshold for survival. Deoxygenation particularly affects cold-water fish, such as trout requires 7 mg of oxygen per liter of water, and salmon requires 6 mg of oxygen per liter. (Warm water species, such as bass and carp, require 5 mg per liter.)

Peter Raymond, a professor of ecosystem ecology at Yale University who peer-reviewed the paper, said: “Even if your oxygen concentration requirements are reduced to a lower level, the performance of individual organisms in the water will be affected.” They The performance is not good. As you can imagine, they become stressed. “

The combination of low oxygen and warm water is particularly worrying. For example, if the temperature and oxygen level are not within the optimal range, it will affect the reproduction time of the fish, thereby affecting their reproduction. Warming water may also strengthen or deactivate their immune systems, which may affect their ability to fight pathogens in a climate-changing environment.

James Whitney, a professor of biology at Pittsburgh State University in Kansas, said that because fish are thermophilic animals, which means that they adjust their body temperature according to the external temperature, their metabolism in warm water will increase, thereby increasing the amount of oxygen they need to survive. Who is not affiliated with the study. “If the situation becomes bad enough, they may suffocate and cause the fish to die,” Whitney said.

For example, during the drought in Kansas in 2018, Whitney recalled that the water in the stream was warmer and the amount of water was reduced due to lack of rain. Fish swallowed oxygen from the surface water, but there was not enough oxygen to wander around and some of them died.

Deoxygenation can become a vicious circle. When lakes are deprived of oxygen, they accumulate sediment at the bottom and then release phosphorus, which triggers the growth of algae on the surface.Lake can Development harmful Algae Bloom, It will consume the remaining oxygen. Some produce toxins that kill fish, mammals and birds; in extreme cases, they can also cause illness or even death in humans.

“It is not hypothetical that organisms will be affected. This will happen,” Raymond said.

He pointed out that although it is not possible to directly add oxygen to the lake, there are other ways to improve the health of the ecosystem. The biggest change must occur at the global level: reducing greenhouse gas emissions will prevent the lake from warming and losing solubility. But local care is also very important. “There is a direct climate impact, but there are many things that can be done locally to maintain high oxygen levels,” Ross agreed.

Ross and several other research co-authors are GLEON (Global Lake Ecological Observation Network), A group of grassroots scientists from all over the world, they focus on protecting freshwater resources. They share data to capture ecosystem changes early, because lakes are among the first to show measurable changes. Some of their suggestions include using data from one lake to understand other lakes and assessing risks based on real-time measurements of local water temperature and dissolved oxygen levels. Planting trees around the lake as a buffer zone can prevent erosion, which can increase water transparency and reduce nutrient loss. This can be coordinated by state agencies that manage water resources or individual lake associations. The Environmental Protection Agency also recommends that residents living near water bodies use fertilizers in accordance with the instructions on the label to prevent excessive nitrogen and phosphorus from entering the lake and unintentionally fertilizing algae reproduction.

“In order to maintain the status quo, active management is needed in the future—or will be needed,” Ross said. What he said by “future” does not mean decades. He meant in the next few years. “This is an ongoing problem,” he said.

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