Lakes viewed as patients

Toxic algae blooms are among the various “health problems” of lakes. © Angelina Tittmann, IGB

A medical perspective can benefit water protection, say researchers: In their study, they illustrate the problems of the world’s lakes and their solution strategies by drawing parallels to human health. They show, for example, how lakes can also suffer from problems with circulation, breathing and nutrition or are affected by infections. To protect lakes from or cure such “afflictions,” strategies similar to medical practices are also needed, the scientists say.

Their importance for nature and people is enormous: there are 1.4 million bodies of water worldwide that are known as lakes and have a surface area larger than ten hectares. In addition to the complex ecosystem services, many of them also play an important role in fisheries as well as in the drinking water supply and recreation of millions of people. But many of the world’s lakes are in danger: due to local and global trends, some are already in very poor condition or are heading towards this.

In their study, researchers led by Gesa Weyhenmeyer from Uppsala University evaluated LakeATLAS data on lakes around the world in order to develop a current picture of the conditions, developments and threats to the world’s lakes. The special thing about this is that they specifically used terms and approaches from human health to describe the results. “We want to make it clear that lakes are living systems that need oxygen, clean water and a balanced supply of energy and nutrients. The primary reason for adopting the terms is to increase awareness and understanding of global lake health issues,” the authors write.

Circulatory problems, infections…

As they report, in addition to “poisoning” from chemicals and garbage, many lakes are affected by severe “circulatory problems”: This is what the researchers describe as impairments that affect the supply and dynamics of water. According to them, severe water deficits are the worst because they are associated with numerous cascading effects on the health of the lakes. In their study, the researchers estimate that around 115,000 lakes worldwide lose twice as much water through evaporation as they receive through direct precipitation. If inflows can no longer compensate for this, drying out occurs. The researchers report that 153 million people live near lakes that are affected by this.

According to them, another widespread health problem in the world’s lakes is “improper nutrition”: Disturbances in the nutrient balance of a lake can lead to complex impairments in its ecosystem services. Excessive nutrient intake can lead to problematic algae blooms. In some cases, these can be toxic organisms that, in addition to causing ecological damage, also endanger drinking water production. The main cause of the excessive nutrient intake is domestic, industrial and agricultural inputs.

On the other hand, certain human-caused effects can also lead to malnutrition, the researchers report. In turn, “pathogens” can play a role: an example of this is the invasive quagga mussel, which has been introduced into many lakes. If they multiply en masse, they can filter the lake water so intensively that the nutrient content drops too much. Living creatures such as fish can no longer find enough food in an affected body of water and overall productivity drops to a level that no longer corresponds to optimal water health.

Some multimorbid patients

However, a much more common health problem in many lakes is “shortness of breath,” the researchers write: Low oxygen levels occur primarily at high temperatures, weak water circulation and high biomass production. The deficiency can severely impair the development of small creatures and fish or even lead to their suffocation. The researchers’ evaluations show that more and more lakes around the world are affected by such a critical lack of oxygen. According to them, climate change can also play a significant role: Even lakes with good water quality can increasingly find themselves in “shortness of breath” because milder winters lead to incomplete mixing of the lake water.

Many lakes also struggle with multiple health problems at the same time. They can therefore be described as “multimorbid” – analogous to humans, say the researchers. According to them, a systematic assessment concept of the state of health can also be based on medical models. “For example, we propose a classification in a multi-stage system from critical to excellent based on defined vital functions,” says Weyhenmeyer. The researchers say that human health care strategies can also be used to protect and treat threatened lakes: prophylaxis, regular screening, treatment and damage limitation.

Finally, co-author Hans-Peter Grossart from the Leibniz Institute for Freshwater Ecology and Inland Fisheries in Berlin says: “If the health problems of the lakes remain untreated, important ecosystem services will no longer be available or will only be partially available, which will jeopardize the well-being of millions of people endangered. We therefore recommend coordinated, cross-sectoral and multidisciplinary prevention and treatment strategies.”

Source: Leibniz Institute for Freshwater Ecology and Inland Fisheries, specialist article: Earth’s Future, doi: 10.1029/2023EF004387

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