Bioturbation frequency alters methane emissions from reservoir sediments

Area of Science:

• Environmental Science
• Geochemistry
• Ecology

Background:

• Inland aquatic systems significantly contribute to global greenhouse gas (GHG) emissions.
• Bioturbation, the disturbance of sediments by organisms, influences biogeochemical processes and GHG release.
• The frequency of bioturbation may alter the rate and type of GHG emissions from aquatic sediments.

Purpose of the Study:

• To investigate the impact of varying bioturbation frequencies on methane (CH4) and carbon dioxide (CO2) emissions from reservoir sediments.
• To test the hypothesis that intermediate bioturbation frequency maximizes CH4 release, while frequent disturbance favors CO2 release.

Main Methods:

• Laboratory mesocosms with homogenized reservoir sediment were subjected to simulated bioturbation at 3, 7, 14, or 21-day intervals, plus a control (0 days).
• Greenhouse gas emission rates (ebullition and diffusion) were measured for each treatment.
• Mechanical disturbance simulated the physical effects of bioturbation.

Main Results:

• An intermediate disturbance frequency (7-day intervals) resulted in the highest total GHG emission rates.
• Both the most frequent (3-day) and least frequent (0-day) disturbance intervals reduced overall GHG emissions compared to weekly disturbance.
• Methane (CH4) ebullition was the primary driver of emission patterns, with no significant relationship observed between disturbance frequency and diffusive CO2 emissions.
• Most GHG ebullition occurred during disturbance events, indicating mechanical release of trapped bubbles.

Conclusions:

• Bioturbation frequency significantly affects GHG emissions from reservoir sediments, with non-linear responses in CH4 emissions.
• Intermediate disturbance frequencies can maximize CH4 release, a critical factor for understanding aquatic GHG budgets.
• The variable effects of disturbance frequency may explain discrepancies in previous bioturbation studies and highlight its role in within-system GHG emission variability.