No.9 of the journal Transactions of the Karelian Research Centre RAS, Limnology and Oceanology Series, came out of press at the end of September and is also available on the KarRC RAS website. Contributions were submitted by scientists from Petrozavodsk, Arkhangelsk, Omsk, St. Petersburg, Tomsk, Apatity, and Minsk. The lineup totals 13 scientific articles.

The paper "Equilibrium density profiles and thermocline depth in lakes during the period of summer stratification" by Dr. Sergey Bogdanov, Leading Researcher at the Northern Water Problems Institute KarRC RAS, presents an attempt to construct a hydrostatically stable equilibrium profile using variational calculus methods, where the criterion for selecting an asymptotically realizable profile among profiles with acceptable energy characteristics is that it corresponds to maximum entropy.

Seasonal and spatial changes in water turbidity of Lake Munozero indicate a significantly increased human impact on the lake’s northern region, where elevated water column turbidity is observed in the summer and suspended matter is accumulated near the bed in the fall, posing a threat for a lake with slow water turnover. This is the conclusion reached by the authors of the paper "Seasonal and spatial variability of temperature and turbidity in a deep dimictic lake", Researchers of the Northern Water Problems Institute KarRC RAS, Roman Zdorovennov and Galina Zdorovennova. The scientists believe that, considering the unique composition and purity of the Lake Munozero water, which must be preserved, it is clearly time to raise the issue of reducing economic impact on this water body.

Analysis of surface-air temperature observation data from three weather stations in Karelia covering the period 1953–2024 points to a persistent and steady trend for regional climate warming along Lake Onego across all seasons, with the most pronounced warming in winter. Over this 70-year period, it has resulted in a shortening of the ice-covered period in bays by 35 days, and a 2.4–3.2 °C increase in the average water temperature in bays from June through October. This is the finding reported by the authors of the article "Features of the thermal and ice regime of Lake Onego bays based on long-term observations", Researchers of the Northern Water Problems Institute KarRC RAS Tatyana Efremova, Nikolai Palshin, and Head of the Karelian Centre for Hydrometeorology and Environmental Monitoring Tatyana Kravchenkova.

Scientists from the N.P. Laverov Federal Centre for integrated Arctic Research, RAS Ural Branch (Arkhangelsk) Kseniya Titova, Natalya Kokryatskaya, and Tatyana Zhibareva summarized the results of studies on anaerobic processes (showcasing sulfate reduction) in sediments of two hydrographically connected small boreal lakes in the Arkhangelsk Region, one of which is under anthropogenic load and the other is in a near-natural state. Having performed a comparative analysis of the quantitative parameters of the sulfate reduction process (concentrations of reduced sulfur compounds, organic carbon, and reactive iron), they show that the content and ratio of reduced sulfur forms in Lakes Verkhneye and Nizhneye can serve as a marker of anthropogenic impact on the water body. Based on the data, the environmental situation in Lake Nizhneye can be described as poor, while the situation in the hydrographically connected Lake Verkhneye is generally favorable.

Scientists from the Siberian State Automobile and Road University (SibADI, Omsk) Alexander Korolev and Svetlana Lovinetskaya presented the results of hydrochemical surveys of nine small lakes located in the Poltavsky Municipal District, Omsk Region, and assessed their environmental state. They surveyed small water bodies of natural genesis. Physicochemical, morphometric, and mathematical statistics methods were applied to each lake.

An article assessing the current radioecological state of bottom sediments in the northeastern part of the Barents Sea was contributed by scientists of the Laverov Federal Centre for Integrated Arctic Research, RAS Ural Branch (Arkhangelsk) Evgeny Yakovlev and Andrey Puchkov together with Master's Student at St. Petersburg State University Angelina Lipkina. The author report that, according to the surveys conducted during the Arctic Floating University marine expedition in July 2024, the activity of native radionuclides is within the ranges characteristic of the region. The levels of technogenic radioactive contamination are below the Barents Sea average. Their data indicate an absence of recent inputs and a general trend toward a decrease in anthropogenic radioactive contamination. Calculation of radiological safety indices showed that the current levels of natural radioactivity do not pose a threat to marine ecosystems. The new data provide a relevant background framework for monitoring the Arctic shelf in the context of its planned industrial development and ongoing climate change.

A large team of scientists from the Scientific and Practical Centre for Bioresources of the National Academy of Sciences of Belarus, Belarusian State University, and Tomsk State University performed a comparison of the structural organization of zooplankton in Lake Dolgoe (Belarus) in the periods of summer stratification and spring homothermy. The authors underscore the importance of studying zooplankton for understanding the functioning of lake ecosystems, assessing biodiversity, and tackling practical tasks related to fish farming, ecological monitoring, and protection of water resources. The surveys revealed a twice higher total abundance of zooplankton in summer vs. spring. The lower spring abundances were due to the low numbers of cladoceran crustaceans in this season. Another finding is that the concentration of organisms generally remained the highest in the upper water layers in both seasons, but near-surface abundances accounted for up to 50% of the water-column total in the summer and only 25% in the spring.

The paper by Nikolai Usov, affiliated with the RAS Zoological Institute (St. Petersburg) and the Northern Water Problems Institute of the Karelian Research Centre RAS, deals with the current state of mesozooplankton in Blagopoluchiya Bay (Bolshoy Solovetsky Island, Solovetsky Archipelago). Surveys conducted in June 2025 and in August 2024 and 2025 revealed a decrease in total zooplankton abundance, with a particularly sharp decline observed in August 2024 and 2025 in the immediate vicinity of the spot where sewage from the Solovetsky community enters the bay. The author concludes that the most likely cause of the decrease in zooplankton abundance in the inner part of Blagopoluchiya Bay is anthropogenic pollution of this water area. In addition, the inner bay was found to harbor the alien species Eurytemora americana, which reaches high abundances in summer. This may indicate that the species has great potential for colonizing brackish coastal areas of the White Sea.

A group of scientists from the Russian State Hydrometeorological University (St. Petersburg) surveyed 8 of the 11 lakes of Valaam Island. They conducted the first ever ichthyological fieldwork at lakes Nikonovskoye and Leshchevoye; produced the first description of the species composition of the fish community of Lake Nikonovskoye, and carried out a few other studies. The scientists argue that their results would be useful in developing a bioindication system for small lakes of Karelia and modeling Valaam Archipelago’s aquatic ecosystems.

The next issue of the Transactions of KarRC RAS Limnology and Oceanology Series will be published in 2027.