Effects of increasing temperatures on methane concentrations and methanogenesis during experimental incubation of sediments from oligotrophic and mesotrophic lakes

Abstract

Global warming is expected to raise temperatures in freshwater lakes, which have been acknowledged to contribute up to 10% of the atmospheric methane concentrations. Increasing temperature enhances methane production and oxidation rates, but few studies have considered the balance between both processes at experimentally higher temperatures within lake sediments. The temperature dependence of methane concentrations, methane production rates, and methanogenic (mcrA) and methanotrophic (pmoA) community size was investigated in intact sediment cores incubated with aerobic hypolimnion water at 4, 8, and 12°C over 3 weeks. Sediment cores of 25 cm length were collected at two temperate lakes—Lake Stechlin (Germany; mesotrophic‐oligotrophic, maximum depth 69.5 m) and Lake Geneva (France/Switzerland; mesotrophic, maximum depth 310 m). While methane production rates in Lake Stechlin sediments did not change with increasing temperatures, methane concentrations decreased significantly. In contrast, methane production rates increased in 20–25 cm in Lake Geneva sediments with increasing temperatures, but methane concentrations did not differ. Real‐time PCR demonstrated the methanogenic and methanotrophic community size remained stable independently of the incubation temperature. Methane concentrations as well as community sizes were 1–2 orders of magnitude higher in Lake Stechlin than in Lake Geneva, while potential methane production rates after 24 h were similar in both lakes, with on average 2.5 and 1.9 nmol g−1 DW h−1, respectively. Our results suggest that at higher temperatures methane oxidation could balance, and even exceed, methane production. This suggests that anaerobic methane oxidation could be involved in the methane balance at a more important rate than previously anticipated.

Exceptional summer warming leads to contrasting outcomes for methane cycling in small Arctic lakes of Greenland

“…In addition to changes to thermal structure, warming and thawing of permafrost in the Arctic may allow organic carbon, nutrients, and ions that were previously frozen in sediments to be transported into aquatic systems and become available for microbial utilization (Kokelj et al, 2009;Lougheed et al, 2011;Weyhenmeyer et al, 2011). Experimental laboratory incubation studies have also demonstrated that microbial CH 4 production significantly increases with increased temperature (Duc et al, 2010;Lofton et al, 2013;Fuchs et al, 2016).…”

Microbial communities from Arctic marine sediments respond slowly to methane addition during ex situ enrichments

“…Fundamentally, it can be quite challenging to conduct controlled long‐term experiments in the field, and these experiments may also be subject to some bias. By using laboratory experimentation to study microbial communities under defined conditions, such as increases in temperature (Fuchs et al ., ) or organic matter concentrations (Babbin et al ., ), novel insight can be gained into causal relationships among biogeochemical processes that exist in nature, and how these processes might be expected to change in response to environmental stimuli. Ideally, both controlled laboratory enrichments and careful experiments performed at field sites can function together as complementary approaches to resolve difficult microbial ecology issues.…”

Persistence of bubble outlets in soft, methane‐generating sediments

“…Both of the latter two effects may have been caused by reconstituting of the sediments. Previous studies have demonstrated the temperature dependence of methane generation and emissions [ Crill and Martens , ; Yvon‐Durocher et al , ], although in some cases the resultant increase in methane oxidation can balance this effect and even reduce sediment methane concentrations [ Duc et al , ; Fuchs et al , ]. The sonar may also underestimate fluxes due to limitations in sensitivity to small bubbles, though those did not contribute significantly to the flux in the tank (Figure ).…”