Seasonal and Spatial Dynamics of Gas Ebullition in a Temperate Water‐Storage Reservoir

• Published in: Water resources research 2017-10, Vol.53 (10), p.8266-8276
• Main Authors: Tušer, Michal, Picek, Tomáš, Sajdlová, Zuzana, Jůza, Tomáš, Muška, Milan, Frouzová, Jaroslava
• Format: Article
• Language: English
• Subjects: Acoustic surveying; Carbon budget; Climate change; Dynamics; ebullitive flux; Fluxes; Gas composition; Global warming; hydroacoustics; Impoundments; Inflow; Methane; Organic matter; river impoundment; Rivers; season; Seasonal variations; Seasonality; Seasons; Sediments; Spatial distribution; spatiotemporal scale; Stochasticity; Storage reservoirs; Surveying; Water depth; Water inflow; Water storage
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2017WR020694

Gas ebullition of river impoundments plays an increasingly significant role, particularly in transporting methane CH4 from their sediments to the atmosphere, and contributing to the global carbon budget and global warming. Quantifying stochastic and episodic nature of gas ebullition is complicated especially when conventionally conducted by using coverage‐limited gas traps. Current knowledge of seasonality in a reservoir's gas ebullition is lacking in the literature. For this reason, advanced acoustic surveying was intensively applied to determine spatiotemporal distributions of gas ebullition in a European water‐storage reservoir for two years. Additionally, the sampling was accompanied with gas collecting for analyzing gas composition. The gas released from the reservoir was primarily composed of CH4 (on average 52%, up to 94%). The longitudinal distribution of gas ebullition was mainly determined by a proximity to the river inflow as a source of organic matter. A magnitude of ebullitive fluxes within the reservoir varied up to 1,300 mL m−2 d−1 (30 mmol CH4 m−2 d−1). The most significant period of ebullition has turned out to be in fall, on average reaching a sevenfold ebullitive flux (70 mL m−2 d−1, 1.6 mmol CH4 m−2 d−1) higher than in the rest of the season. A substantial contribution to the fall peak was induced by an expansion of gas ebullition into greater depths, covering two thirds of the reservoir in late fall. The study demonstrates that the ebullitive fluxes of the temperate water storage reservoir were correlated to season, depth, and inflow proximity. Key Points Fall favors gas ebullition in a temperate water‐storage reservoir The longitudinal distribution of gas ebullition was mainly related to a the proximity of the river inflow Expansion of bubbling areas further into the reservoir's depths followed the annual thermal maximum of water above sediments