Influence of Hydrometeorological Conditions on Methane Content and Emission in the Ivankovo Reservoir During the Summer Period
Lada Peshkicheva
ABSTRACT
The Ivankovo Reservoir, part of the Volga-Kama cascade, serves as a key source of greenhouse gas emissions, particularly methane (CH₄), which has a global warming potential 28 times that of CO₂. The present study investigates the impact of hydrometeorological conditions on methane content and emission during summer periods from 2020 to 2024. Key parameters influencing methanogenesis— temperature, precipitation, water levels, flow rates, and oxygen levels—exhibited marked variability: air and water temperatures rose from averages of 20°C (2020) to peaks of 25-30°C (2024), with amplitudes increasing by 50% due to prolonged heatwaves; precipitation was uneven, ranging from droughts (e.g.,<50 mm/month in July 2022) to peaks (243 mm/month in July 2023), correlating with flow variability (exchange coefficients 0.85-1.13, lowest in dry years); water levels declined to 121 m BS in 2022/2024, fostering hypoxia (<2 mg/L O₂ in 70% of bottom waters by 2024 vs. 30% in 2020). These conditions enhanced methanogenesis in hot, dry, low-flow periods by promoting anoxic sediments and organic matter accumulation, yielding peak concentrations (up to 2432.7 µg/L) and fluxes (up to 33967 mg CH₄ m⁻² day⁻¹). Conversely, wet, high-flow periods increased aeration and dilution, suppressing emissions by up to 80%. Spatial differentiation across zones revealed higher methanogenesis in shallow, organic-rich floodplain and macrophyte areas (e.g., 138.9 µg/L vs. 47.2 µg/L in channel at Shosha, June 2024) compared to sandy channel zones like Gorodnya (15.4 µg/L average); lake-like, low-flow zones such as Korcheva showed 2-5x higher bottom concentrations due to persistent anoxia. Macrophytes contributed significantly via aerenchyma transport, amplifying fluxes in vegetated shallows. Total emissions ranged from 1.38 t CH₄ day⁻¹ (May 2023) to 151.94 t CH₄ day⁻¹ (August 2024). Balance calculations indicate sediment release as the primary input (up to 674 t CH₄ day⁻¹ in August 2024), with net accumulation in hypoxic conditions. Findings highlight the need for water level management to mitigate emissions amid climate change.
