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E-Thesis 145 views

Microbial Methane Production in Oxic Lake Waters / MARCO GUNTHEL

Swansea University Author: MARCO GUNTHEL

  • Redacted version - open access under embargo until: 31st March 2023

DOI (Published version): 10.23889/Suthesis.53897

Abstract

Microbial methane production is commonly believed to be an exclusively anaerobic process performed by methanogenic Archaea, but the recent discovery of methane production in oxygenated waters challenges this paradigm and demands re-assessments of the global methane cycle. There are important questio...

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Published: Swansea 2019
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Tang, Kam W. ; Flynn, Kevin
URI: https://cronfa.swan.ac.uk/Record/cronfa53897
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Abstract: Microbial methane production is commonly believed to be an exclusively anaerobic process performed by methanogenic Archaea, but the recent discovery of methane production in oxygenated waters challenges this paradigm and demands re-assessments of the global methane cycle. There are important questions regarding this newly recognized methane source: What are the environmental controls? Who are the responsible organisms? What are the underlying pathways? Is this phenomenon of global relevance? This thesis shows that oxic methane production was a recurring phenomenon in the seasonally stratified oxic water column of Lake Stechlin. Sunlight exposure and phosphorus limitation promoted oxic-water methane accumulations in situ. Bacteria (Cyanobacteria) and Algae (Diatoms, Green Algae, Cryptophytes) produced methane from 13C-labelled bicarbonate in incubation experiments, indicating that oxic methane production was associated with autotrophic carbon fixation. Further, correlations between water column methane concentrations and phytoplankton pigments were observed on the diurnal and seasonal scales. Together, these findings suggest that oxic methane production is a common feature of phytoplankton and likely relevant for limnic systems in general. Balancing the system-wide methane sources and sinks of Lake Stechlin’s surface mixed layer shows the oxic methane source was a substantial contributor to atmospheric methane emission with pronounced short-term dynamics. In addition, empirical modelling based on results presented here and available literature data reveals that oxic methane production in lake waters has global implications: The oxic methane source is predicted to be the primary source of atmospheric methane emission from the mid-water column in lakes larger than 1 km2. Furthermore, the explanatory power of the widely used wind-based models for estimating water-to-air gas emission was much improved by incorporating water- and air temperatures as additional proxy parameters. This thesis shows that oxic methane production is important to lake methane cycling, and global assessments like the upcoming IPCC report should acknowledge the oxic methane source.
Item Description: Chapters 2 and 4 of the Ph.D. thesis have been radacted. They already have been published by various scientific journals or are in the process of being published.
Keywords: oxic methane source, oxygenated water, lake CH4 budget, phytoplankton, photosynthesis, methane emission, surface flux parameterisation, Lake Stech/in