PRJNA766591
Acton lake sediment: Bioturbation Microcosms Raw sequence reads
Methane emissions from aquatic ecosystems are increasingly recognized as substantial, yetvariable contributions to global greenhouse gas emissions. This is in part due to the challenge of modeling biologic parameters that affect methane emissions from a wide range of sediments. For example, the impacts of fish bioturbation on methane emissions in the literature have been shown to result in a gradient of reduced to enhanced methane emissions from sediments, however, it is likely that variation in experimental fish density, and consequently the frequency of bioturbation by fish likely impacts this outcome. To explore how the frequency of disturbance impacts the levels of methane emissions and the corresponding microbial communities associated with producing methane, we quantified greenhouse gas emissions and microbial community composition in sediment microcosms treated with various frequencies of mechanical disturbance, analogous to different levels of activity in benthic feeding fish. Greenhouse gas emissions were largely driven by methane ebullition and were highest for the intermediate disturbance frequency (disturbance every 7 days). The lowest emissions were for the highest frequency treatment (3 days). In terms of total microbial community structure, no statistical difference was observed in the community structure of any disturbance treatment (0, 3, 7, 14 days) or sediment depth (1 cm, 3 cm) measured. Looking specifically at methanogenic Archaea however, a shift towards greater relative abundance of a putatively oxygen-tolerant methanogenic strain (ca. Methanothrix paradoxum) was observed for the highest frequency treatments and at depths impacted by disturbance (1 cm). This was further supported by a linear decrease in quantitative abundance of methanogens (assessed by qPCR of the mcrA gene) with increased disturbance frequency in bioturbated sediments (1 cm) opposed to those below the zone of bioturbation (3 cm). This suggest that the disturbance treatments affected methanogen populations, likely through oxygen exposure. However, total methane emissions were not simply a function of methanogen populations and were likely impacted by the residence time of methane in the lower frequency disturbance treatments. Low frequency mechanical disruption results in lower methane ebullition compared to higher frequency treatments which in turn resulted in reduced overall methane release and likely enhanced methanotrophic activities. The impacts of disturbance on methanotrophic communities will be the subject of follow up work