Do not break with water: the "microbial framework" will turn abandoned reservoirs into healing lakes

Scientists from the Siberian Federal University and the Institute of Biophysics of the Siberian Branch of the Russian Academy of Sciences, together with foreign colleagues, have found out over the course of many years of research what happens to deep natural reservoirs when their layers are completely mixed. It turned out that the key role in restoring the basic functions of the microbiota is played by the so—called microbial framework, a set of bacteria that support the stability of the ecosystem. The results of the work can create prerequisites for the management of natural reservoirs and the development of resort lakes with specified properties. However, maintaining such facilities will require complex engineering solutions, and claims about medicinal properties must be based on scientific evidence, experts warned.

What causes lakes to mix?

The study was conducted on the example of Lake Shira in Khakassia. As a result of the complete mixing of its layers, toxic hydrogen sulfide, which had accumulated in the deep waters for many years, disappeared after contact with the upper layers. At the same time, the microbiota of the reservoir has changed significantly.

This reservoir is located in the North Minusinsk basin, its area is about 35 square kilometers, and its depth reaches 24 m, experts said. The water contains a complex of minerals, including sodium and magnesium salts, due to which the reservoir has balneological properties. There are also layers of sulfide mud at the bottom, formed as a result of bacterial activity. This mud is used for medicinal purposes. The lake was completely mixed in 2015. It was caused by the early melting of ice and strong winds.

— Usually in lakes with a depth of more than 10 m, the water column is divided into layers. The upper ones are warmer, while the lower ones are colder, and there is less oxygen in them. There are lakes in which the bottom layer almost does not mix with the upper ones. Toxic gases accumulate there, in particular hydrogen sulfide," said Denis Rogozin, head of the study, Deputy Director for Scientific Work at the Institute of Biophysics of the Siberian Branch of the Russian Academy of Sciences, Professor of the Department of Biophysics at SibFU.

Photo: Denis Rogozin

According to him, water at depth is usually characterized by high salinity, therefore it has a high density. Because of this, mixing rarely occurs, and the microbiota's response to such events remains poorly understood. The scientists managed to observe the process thanks to many years of monitoring. Modern methods of DNA analysis and other tools allow us to study in detail the changes taking place in the ecosystem.

— We have been taking samples for several years and got into such a state. We can say that we were lucky when there was a sharp "coup" of the lake. It turned out that during this period, the sulfate—reducing bacteria that produce hydrogen sulfide simply disappeared, and then, when the reservoir restored its structure, reappeared," Denis Rogozin said.

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How microbes survive an environmental cataclysm

The value of the discovery lies in the understanding that the water area returns to normal through the preservation of functions. After the death of some microorganisms, they are taken over by other bacteria, the scientist explained. For example, after the disappearance of some of the bacteria, these functions were performed by other representatives of the microbiota. As a result, the sulfur, nitrogen, phosphorus and other cycles in the lake were not interrupted.

According to the specialist, during the study, scientists identified 21 strains that formed the "microbial framework" of the reservoir. He helped the microbiota survive the ecological cataclysm.

Photo: Denis Rogozin

Lakes like Shira are valuable recreational facilities, the researcher recalled. Thousands of people come here every year to undergo procedures, relax and improve their health. Understanding the processes occurring in the microbiome can help develop mechanisms for preserving the beneficial properties of a reservoir, as well as predict periods of improvement or deterioration of water quality.

In the future, these technologies may make it possible to manage the condition of lakes and purposefully shape certain properties, Denis Rogozin noted. In addition, the knowledge gained can be used to create artificial reservoirs with specified characteristics, for example, at the site of abandoned quarries and depleted mines, as well as in small sea bays and bays with low water exchange.

How to create new resort reservoirs

— General patterns, such as the division into oxygen and oxygen-free zones, the dominance of the sulfur cycle and the presence of a functional microbial framework, are applicable to other similar reservoirs. ""This allows us to use the data obtained to predict the state of lakes, but taking into account local conditions," Vladimir Pinaev, associate professor at the RUDN University Institute of Ecology, member of the Public Council of the Basic Organization of the CIS Member States for Environmental Education, editor—in—chief of the "Resources" magazine, told Izvestia.

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According to him, it is possible to create new "therapeutic" water areas, but maintaining their properties for decades is a separate engineering task. In addition, special legal and economic mechanisms will be required to scale such projects.

— The management of reservoir properties is quite realistic. Specialists are able to regulate salinity, oxygen content, and intake of organic and mineral substances within certain limits. These parameters determine which microorganisms can exist in different layers and what biochemical reactions will occur," explained Sergey Kharitonov, a molecular biologist and researcher at Lomonosov Moscow State University.

There is a fundamental difference between the ability to control the microbiology of a reservoir and the creation of a "healing lake" with specified properties. First, it is necessary to determine which parameters are responsible for the desired properties of water, and then to establish which microbial communities are able to support them. If we are talking about therapeutic effects, they must be confirmed by clinical studies.

— It is important to understand the tasks of lake property management. In the first case, we are talking about natural reservoirs with a valuable and vulnerable ecosystem. It is necessary not to "improve", but to protect: to conduct environmental control, reduce anthropogenic load, prevent pollution and the entry of alien species. A different approach is needed for man-made reservoirs. With proper design, they can be given a new useful function — recreational, environmental, educational, fish farming, wellness, and so on," explained Maxim Timofeev, director of the Research Institute of Biology of Lake Baikal at Irkutsk State University.

Statements about the "healing" properties of reservoirs should be based on the results of scientific research. Quarries where minerals were extracted should also be treated with special attention: heavy metals and residual reagents may remain in them, as well as increased mineralization and excessive acidity.