Sediment trapping by dams creates methane emission hot spots

Area of Science:

• Environmental Science
• Hydrology
• Climate Change Research

Background:

• Inland waters are critical for carbon cycling, contributing significantly to global methane emissions.
• While large reservoirs are known methane sources, the impact of numerous small dams on emissions remains understudied.
• Dams trap organic carbon, creating conditions conducive to methane production.

Purpose of the Study:

• To evaluate the impact of damming on methane emissions in a central European river system.
• To compare methane release rates between riverine and reservoir sections.
• To identify factors influencing methane emissions in dammed river environments.

Main Methods:

• Direct comparison of methane flux measurements between river and reservoir reaches.
• Analysis of sediment accumulation rates in relation to methane production and release.
• Quantification of areal methane emission rates (mmol CH4 m(-2) d(-1)).

Main Results:

• Reservoir reaches exhibited significantly higher methane emissions (19.7 mmol CH4 m(-2) d(-1)) compared to riverine reaches (0.23 mmol CH4 m(-2) d(-1)).
• Emission rates from reservoirs far exceeded previous estimates for temperate systems.
• Sediment accumulation strongly correlated with methane production and ebullitive release.

Conclusions:

• Small dam impoundments act as major methane emission hotspots.
• Sediment accumulation serves as a reliable proxy for estimating methane emissions from small reservoirs.
• These findings suggest that dam-induced methane emissions could increase global freshwater emissions by up to 7%.