The Suhoe Sea Gulf is a unique White Sea water body. Taking into account the risk of contamination of the White Sea with radionuclides as a result of the activities of the domestic and foreign nuclear industry and considering the plans to construct a deep-water part of the Arkhangelsk port on the Kuya River, the content and distribution patterns of natural and man-made radionuclides in the bottom sediments of the Suhoe Sea Gulf need to be studied. The specific activity of radionuclides was measured using a PROGRESS-2000 gamma spectrometer. Statistical processing of the data was performed using the STATISTICA (data analysis software system), version 10 software by StatSoft, Inc. (2011). The average specific activity of²²⁶Ra,²³²Th and⁴⁰K was 6.5 ± 1.4, 14.2 ± 4.3, 416 ± 89, accordingly.¹³⁴Cs and¹³⁷Cs were detected in 4 and 5 samples with a mean specific activity value of 3.3 ± 1.6 and 3.5 ± 1.1, respectively. The highest specific activity values of⁴⁰K are confined to the pelitic deposits. The main driving force in the processes of accumulation and redistribution of²³²Th is gravitational water accumulation and mechanical transfer. The measured values of the specific activity of radionuclides do not exceed those previously determined by other authors in the bottom sediments of the White Sea. Correlation analysis showed a significant relationship between the content of¹³⁴Cs and¹³⁷Cs (0.77, p = 0.05),²³²Th and⁴⁰K (0.67, p = 0.05) and¹³⁷Cs and⁴⁰K (0.84, p = 0.05). Factor analysis allowed two groups of radionuclides to be identified, their content being is determined by different processes:¹³⁴Cs,¹³⁷Cs, and⁴⁰K are jointly controlled by the most powerful factor (50%) and²³²Th is affected by the weaker factor (29 %). Both factors are based on natural processes of radionuclide receipt and redistribution: the first factor reflects the ability of bottom sediments to adsorb⁴⁰K and isotopes of cesium, which are similar in chemical properties, and the second one reflects the natural process of removal by rivers of²³²Th with terrigenous material.

Small intermountain river basins are most suitable for developing new methods to estimate water balance due to their well-defined catchment boundaries, relatively rapid runoff processes, and accessible landscapes for study. In general terms, dissecting the hydrograph of a small mountain river requires calibration of the flow model against multi-year data sets, including (a) glacier mass balance and snow water content, (b) radiation balance calculation, (c) estimation of the groundwater contribution, and (d) water discharge measurements. The minimum primary data set is limited to the precipitation and temperature distributions at the catchment. This approach postulates that the conditions for the formation of all components of river flow are known in advance. It is reduced to calculating the dynamic balance between precipitation (input part) and runoff, ablation, and evaporation (output part). In practice, accurately accounting for the inflow and outflow components of the balance, as well as the impact of regulating reservoirs, can be a challenging task that requires significant effort and expense, even for the extensively researched catchments. Our studies indicate the potential benefits of an approach based on one-time, but detailed, observations of stable isotope composition, temperature, and water chemistry, in addition to standard datasets. This paper presents the results of the 2022–2023 work conducted in the basin of the small mountain river Ala-Archa, located on the northern slope of the Kyrgyz Range in Tien-Shan, which was chosen as an example due to its well-studied nature. Our approach could identify previously unknown factors of flow formation and assess the time and effectiveness of work in similar conditions.