The Selenga expedition on July 7-10, 2025
On July 7-10, 2025, an automobile expedition (led by A.P. Fedotov) within the State Assignment № 0279-2021-0005 “Study of transformations of the state of reservoirs and watercourses of Eastern Siberia in seasonal and long-term aspects under climate change, geological environment and anthropogenic loads” was carried out to the Republic of Buryatia.
The aim of the expedition is study of the seasonal dynamics of the components of the chemical and sanitary-microbiological composition of the waters of the Selenga River and its tributaries in the Russian territory, as well as tributaries of the Southern Baikal. Besideds, to assess the quality of watercourses during the summer period.
The expeditionary team consisted of: I.V. Tomberg, senior researcher, Suslova M.Yu., senior researcher, Zamkovoi F.A., driver.
During the expedition, the samples were collected:
- on the Selenga River, from the border with Mongolia (the settlement of Naushki) to the delta (the settlement of Murzino), including its main tributaries within the territory of Russia (the rivers Dzhida, Chikoi, Temnik, Bayangol, Khilok, and Uda);
- • at the mouth sections of the tributaries of Southern Baikal (rivers Utulik, Solzan, Khara-Murin, Snezhnaya, Pereyomnaya, Mishikha).
A total of 21 samples of the river water were collected. The temperature, pH, and electrical conductivity, and dissolved oxygen content (Tab.) were measured on-site in the water. Samples of river water were filtered and preserved for laboratory analysis to determine the levels of dissolved oxygen, major ions, nitrogen compounds, phosphorus, silicon, and organic matter.
Table – Temperature, hydrogen index, and electrical conductivity in the water of the studied rivers, July 2025.
| Watercourse | Т,ºС | рН | Ес25, mc Cm/cm |
|---|---|---|---|
| Selenga River (Naushki settlement) | 22,1 | 8,20 | 278,0 |
| Selenga River (Zarubino village) | 23,0 | 8,22 | 279,4 |
| Selenga River (Selenduma settlement) | 14,0 | 8,07 | 201,1 |
| Temnik River | 17,2 | 7,73 | 99,55 |
| Bayangol River | 23,2 | 8,27 | 458,5 |
| Selenga River (Novoselenginsk settlement) | 21,2 | 8,21 | 268,2 |
| Chikoi River | 22,8 | 7,91 | 93,36 |
| Selenga River (Dede-Sutoi settlement) | 21,9 | 8,17 | 242,8 |
| Khilok River | 22,1 | 8,29 | 167,4 |
| Selenga River (upstream of Ulan-Ude) | 22,4 | 8,22 | 223,4 |
| Uda River | 21,0 | 8,32 | 155,7 |
| Selenga River (downstream of Ulan-Ude) | 22,1 | 8,15 | 225,8 |
| Selenga River (Kabansk settlement) | 21,6 | 8,20 | 210,5 |
| Selenga River (Murzino village) | 21,4 | 8,20 | 211,1 |
| Utulik River | 13,3 | 7,96 | 204,4 |
| Solzan River | 13,5 | 7,80 | 76,96 |
| Khara-Murin River | 12,9 | 7,56 | 70,56 |
| Snezhnaya River | 15,0 | 7,83 | 92,14 |
| Pereyomnaya River | 14,4 | 7,04 | 60,57 |
| Mishika River | 13,1 | 7,86 | 78,95 |
River waters were studied for sanitary-microbiological indicators: total coliform bacteria (TCB), E. coli and enterococci, according to SanPiN 1.2.3685-21 “Hygienic standards and requirements for ensuring the safety and (or) harmlessness of human habitat factors”, the number of which for surface waters should not exceed 500, 100 and 10 CFU/100 cm3, respectively. TCB is the most sensitive indicator for identifying sources of fecal contamination, including minor ones. The presence of E. coli and enterococci indicates fresh fecal contamination entering the water.
Based on the analysis of the Southern Baikal tributaries, five of six rivers studied met the standards for surface water, where the number of coliform bacteria varied from 6 to 146 CFU/100 cm3, E. coli ranged from 2 to 12 CFU/100 cm3, and enterococci from 4 to 10 CFU/100 cm3. Compared to March, the number increased slightly - 2 times. The maximum values of TCB were recorded in the River Mishikha, with TCB number 2,842 CFU/100 cm3, which exceeded the standard by 5.7 and 1.5 times, respectively.
Research has indicated that all water samples from the Selenga River had exceedances in TCB and enterococci. The TCB number varied from 6,170 (Selenduma settlement) to 36,015 (Murzino settlement) CFU/100 cm3, E. coli – from 0 (Dede-Sutoi settlement) to 300 (Kabansk settlement) CFU/100 cm3, enterococci – from 24 (Naushki settlement) to 340 (downstream of Ulan-Ude) CFU/100 cm3. The maximum number of TCB, E. coli and enterococci exceeded the standards 72, 3 and 34 times, respectively. All the Selenga tributaries studied exceeded the standards for the surface waters, regarding TCB and enterococci. Number of TCB varied from 1 220 to 24,050 CFU/100 cm3, E. coli - from 20 to 200 CFU/100 cm3, enterococci - from 16 to 1,560 CFU/100 cm3. In comparison to March, the minimum values were detected in samples from the Temnik River, while the maximum values were found in the Khilok River, with the exception of the E. coli indicator, which showed the highest count in the water of the Uda River. It was noted that in the Selenga River, the number of coliform bacteria was, on average, twice as high as in the tributaries. Number of TCB is on average two times higher than in tributaries.
According to the obtained data, TCB number and enterococci during the summer period is 28 times and 4.5 times higher, respectively, than in the under-ice period (March 2025).