Effects of turbulence on carbon emission in shallow lakes

Turbulent mixing is enhanced in shallow lakes. As a result, exchanges across the air-water and sediment-water interfaces are increased, causing these systems to be large sources of greenhouse gases. This study investigated the effects of turbulence on carbon dioxide (CO₂) and methane (CH₄) emissions in shallow lakes using simulated mesocosm experiments. Results demonstrated that turbulence increased CO₂ emissions, while simultaneously decreasing CH₄ emissions by altering microbial processes. Under turbulent conditions, a greater fraction of organic carbon was recycled as CO₂ instead of CH₄, potentially reducing the net global warming effect because of the lower global warming potential of CO₂ relative to CH₄. The CH₄/CO₂ flux ratio was approximately 0.006 under turbulent conditions, but reached 0.078 in the control. The real-time quantitative PCR analysis indicated that methanogen abundance decreased and methanotroph abundance increased under turbulent conditions, inhibiting CH₄ production and favoring the oxidation of CH₄ to CO₂. These findings suggest that turbulence may play an important role in the global carbon cycle by limiting CH₄ emissions, thereby reducing the net global warming effect of shallow lakes.