Methane ebullition and diffusion from northern ponds and lakes regulated by the interaction between temperature and system productivity

Abstract

Methane (CH 4 ) emissions from aquatic systems should be coupled to CH 4 production, and thus a temperature‐dependent process, yet recent evidence suggests that modeling CH 4 emissions may be more complex due to the biotic and abiotic processes influencing emissions. We studied the magnitude and regulation of two CH 4 pathways—ebullition and diffusion—from 10 shallow ponds and 3 lakes in Québec. Ebullitive fluxes in ponds averaged 4.6 ± 4.1 mmol CH 4 m −2 d −1 , contributing ∼56% to total (diffusive + ebullitive) CH 4 emissions. In lakes, ebullition only occurred in waters 4 m −2 d −1 , and when integrated over the whole lake, contributed only 18% to 22% to total CH 4 emissions. While pond CH 4 fluxes were related to sediment temperature, with ebullition having a stronger dependence than diffusion (Q 10 , 13 vs. 10; activation energies, 168 kJ mol −1 vs. 151 kJ mol −1 ), the temperature dependency of CH 4 fluxes from lakes was absent. Combining data from ponds and lakes shows that the temperature dependency of CH 4 diffusion and ebullition is strongly modulated by system trophic status (as total phosphorus), suggesting that organic substrate limitation dampens the influence of temperature on CH 4 fluxes from oligotrophic systems. Furthermore, a strong phosphorus‐temperature interaction determines the dominant emission pathway, with ebullition disproportionately enhanced. Our results suggest that aquatic CH 4 ebullition is regulated by the interaction between ecosystem productivity and climate, and will constitute an increasingly important component of carbon emissions from northern aquatic systems under climate and environmental change.

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