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Fisheries Science of Ukraine, 2026; 2(76): 70-98
DOI: https://doi.org/10.61976/fsu2026.02.070
UDC 556.5:556.3(477.6)

Received: 04.04.2026
Received in revised form: 19.05.2026
Published: 30.06.2026

Hydrological-hydrochemical transformations of the Vovcha River under conditions of climate change, cascade regulation and military actions as determinants of the state of ichthyofauna: forecast until the end of the 21st century

D. Dovhanenko, This email address is being protected from spambots. You need JavaScript enabled to view it. , ORCID ID 0000-0003-1440-9344, Communal Institution of Higher Education «Dnipro Academy of Continuing Education», Dnipro
S. Serdiuk, This email address is being protected from spambots. You need JavaScript enabled to view it. , orcid ID 0009-0005-7886-6183, Dnipro State Agrarian and Economic University, Dnipro
K. Okhotnyk, This email address is being protected from spambots. You need JavaScript enabled to view it. , orcid ID 0009-0006-0841-7996, The International HCH & Pesticides Association, Holte, Denmark
R. Novitskyi, This email address is being protected from spambots. You need JavaScript enabled to view it. , ORCID ID 0000-0001-9373-5759, Dnipro State Agrarian and Economic University, Dnipro

Purpose. To substantiate the forecast of the hydrological and hydrochemical regime of the Vovcha River (Samara River basin, Dnieper basin) based on the climate-runoff balance model and the RCP 4.5 and RCP 8.5 climate scenarios (IPCC AR6), taking into account the cascading regulation of the runoff, military operations, and to assess the transformation of the ichthyological complex for the period up to 2100.

Methodology. The mathematical model “climate-runoff” based on the water-heat balance equation of V. S. Mezentsev was applied. The retrospective analysis is based on the ERA5 reanalysis; the forecast calculations are based on the CORDEX Core-11 (0.11°) regional climate models for the RCP 4.5 and RCP 8.5 trajectories. Spatial analysis was performed in QGIS using the SRTM 30 DEM. Hydrochemical analysis is based on state monitoring data of the Vovcha River for 2014–2021. The state of the ichthyofauna is characterized based on the results of field research in 2025 and retrospective materials (2005).

Findings. The climatic runoff rate of the Volcha River is 17.5 mm; it spatially varies from 10.5 mm to 31.4 mm. Under RCP 4.5, in 2021–2040, the runoff will decrease by 5%, by 2100 – to 13.7 mm (–25–(–40)%). Under RCP 8.5, in 2021–2040, the average decrease will reach –34% (–55% at the mouth), in 2041–2100, the runoff will critically decrease to 8 mm (Ymin = 4.5 mm). The predominant hydrochemical type is chloride-sulfate calcium-sodium (sulfate class, sodium group, type II according to O. O. Alekin); mineralization is 2.5–4.8 g/dmі with a tendency to increase. A constant exceedance of fishery MPCs was recorded for Mn (7.0 MPC), Cu (3.2 MPC), Zn (3.7 MPC) and Cr (3.6 MPC), and occasional exceedances for phosphates and nitrites. Military actions made field monitoring impossible. Thirty two fish species from 8 families were discovered in the water area of ​​the Volcha River, among which 11 species have a protected status (RBU, IUCN, Bern Convention).

Originality. For the first time, a spatially detailed quantitative forecast of changes in climatic runoff by 2100 was obtained for the Volcha River basin under two RCP scenarios with a simultaneous analysis of the transformation of the hydrochemical regime under conditions of cascading overregulation and full-scale military operations; the synergistic effect of runoff reduction and increased mineralization of mine discharges on the self-purification capacity of the river and its ichthyological complex was quantitatively characterized.

Practical Value. The results are a scientific basis for developing adaptive strategies for water resources management in the region, forming monitoring programs for the middle rivers of the steppe zone of Ukraine, restoring water management infrastructure in conditions of armed conflict, and substantiating measures for the ecological reconstruction of degraded aquatic ecosystems.

Keywords: runoff, RCP 4.5, RCP 8.5, hydrochemistry, aquacide, water resources, toxic impact, ichthyofauna.

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