Estimating Drivers and Pathways for Hydroelectric Reservoir Methane Emissions Using a New Mechanistic Model

Abstract

Hydroelectric power is the dominant source of renewable energy globally. In 2017, it comprised 13% of global electricity production in OECD (Organization for Economic Co-operation and Development) countries (International Energy Agency, 2018), and 2.5% of global energy production. While electricity from hydropower can replace electricity from carbon-intensive sources such as coal and gas, reservoirs also emit methane (CH 4 ) which could negate some of the carbon benefits of switching to hydropower. CH 4 is a potent greenhouse gas with >32 times the warming potential of carbon dioxide over a 100-year time horizon (Etminan et al., 2016). Prior global CH 4 emissions estimates suggest 3 Tg C of CH 4 yr −1 is released from reservoir surfaces (Barros et al., 2011). This estimate increases to 13.3 Tg C as CH 4 yr −1 after accounting for spillways, turbines, river reaches below dams, and periodically inundated drawdown areas around the reservoir (Li & Zhang, 2014). While useful, these estimates are based on empirical relationships between emissions and potential drivers, and do not provide a process-based understanding of the main drivers and pathways for reservoir CH 4 production and releases, which would aid in development of mitigation strategies. Here we develop, evaluate, and apply a new mechanistic model of the processes driving global hydroelectric reservoir CH 4 emissions.

Including Methane Emissions from Agricultural Ponds in National Greenhouse Gas Inventories

“…17 As for agricultural ponds, reservoirs are also the focus of research to estimate their contributions to anthropogenic methane emissions more accurately. 30 Compared to reported statistics for established reservoirs in the 2024 national GHG inventory for the year 2022, agricultural ponds occupy 56% less surface area (173 vs 394 kha), yet they emit twice as much methane per area (0.238 vs 0.119 t CH 4 ha −1 ) and similar methane in total (41 vs 47 kt CH 4 year −1 ). However, emissions from established reservoirs have increased by 147% from 1990 to 2022 (from 19 to 47 kt CH 4 year −1 ), against the 58% increase (from 26 to 41 kt CH 4 year −1 ) from agricultural ponds.…”

Linking Sediment Gas Storage to the Methane Dynamics in a Shallow Freshwater Reservoir

“…Both degassing and ebullition fluxes are variable across different reservoirs. Median degassing flux was reported as one order magnitude lower than ebullition flux (Deemer et al., 2016); however, a modeling approach showed that for stratified hydropower reservoirs the degassing can be up to four times higher than ebullition (Delwiche et al., 2022). Temporally, considering monthly fluxes, the share of ebullition and degassing to the total CH 4 emissions was variable.…”

Inland Water Greenhouse Gas Budgets for RECCAP2: 1. State‐Of‐The‐Art of Global Scale Assessments

“…(2011)). CH 4 emissions from turbines and from anoxic hypolimnic water released from dams have been shown to be important emission paths (Delwiche et al., 2022; Harrison et al., 2021; Teodoru et al., 2015), but are still ignored in most global scale assessments. Less is known about the key drivers of river CH 4 flux.…”

“…Ebullition is usually reported to be the major emission path with flux rates nearly one order of magnitude higher than that of diffusion on average (Bastviken et al, 2011), though being less important in deeper parts of standing water bodies (>12 m depth in the study by Grinham et al (2011)). CH 4 emissions from turbines and from anoxic hypolimnic water released from dams have been shown to be important emission paths (Delwiche et al, 2022;Harrison et al, 2021;Teodoru et al, 2015), but are still ignored in most global scale assessments. Less is known about the key drivers of river CH 4 flux.…”