Methane (CH4) and nitrous oxide (N2O) are important greenhouse gases with a warming potential 34 and 298 times higher, respectively, than that of CO 2 on a 100-year timescale. Both gases increased rapidly in atmospheric abundance during the last decade, with a significant portion of the CH4 and N2O coming from freshwaters and marine ecosystems. In aquatic environments, the production and consumption of CH 4 and N 2 O is tightly controlled by microbial activity. Microbes performing these reactions inhabit both water column and sediments, attach to particles and live in symbiosis with animals. Their activity occurs under both oxic (e.g., methane oxidation, ammonia oxidation) as well as anoxic conditions (e.g., methanogenesis, anaerobic methane oxidation, denitrification). However, recent findings challenge many traditional ideas about CH 4 and N 2 O cycling. For example, CH 4 is also produced in oxic environments by various bacteria and phytoplankton, while N 2 O is consumed in oxic conditions by oxygen tolerant denitrifying or dinitrogen fixing microbes. At the same time, not only microbes, but abiotic reactions may be also responsible for greenhouse gas production. Aquatic ecosystems are currently under tremendous pressure due to globally increasing temperatures and nutrient loads, with a concomitant decrease in oxygen levels. Therefore, the response to these changing conditions may affect the production and consumption of CH 4 and N 2 O in these ecosystems. In this session, we aim to combine our knowledge of microbial greenhouse gas metabolism, including the production, consumption, and fluxes of methane and nitrous oxide in aquatic environments, as well as the underlying microbial communities and interactions among them, in order to assess the controlling factors for greenhouse gas fluxes in the light of climate change. We therefore encourage contributions that address the biogeochemistry and microbiology to all aspects of ongoing experimental, field and modeling work, including molecular-based or isotope labelling studies, as well as flux quantification.
Lead Organizer: Elizabeth Leon-Palmero, University of Southern Denmark & Princeton University (eleonpalmero@protonmail.com)
Co-organizers:
Sina Schorn, Max Planck Institute for Marine Microbiology (sschorn@mpi-bremen.de)
Bess B. Ward, Princeton University (bbw@princeton.edu)
Jana Milucka, Max Planck Institute for Marine Microbiology (jmilucka@mpi-bremen.de)
Carsten J. Schubert, Swiss Federal Institute of Aquatic Science and Technology (EAWAG) (carsten.schubert@eawag.ch)
Presentations
08:30 AM
Patterns and processes of methane production and oxidation in shallow lakes under different nutrient and warming treatments (6324)
Primary Presenter: Chiara Esposito, Aarhus University (che@ecos.au.dk)
In shallow lakes, methane (CH4) is mainly produced in the anoxic sediment by methanogenic archea and eutrophication and rising temperature generally increase CH4 emissions, while higher rooted plant abundance generally reduce them. The mechanisms behind the latter are not clear, with the action of methane-oxidizing bacteria (MOB) associated with plants and oxidized rootzone a possible cause. Little is also known about the combined effect of temperature and nutrients on CH4 production/oxidation and how their balance shapes emissions. We then tried to define a CH4 total budget in shallow lakes, by determining CH4 production/oxidation patterns across habitats at different temperature, nutrient levels and macrophyte abundance. The experiment took place at the world’s longest running shallow lake mesocosm system at AU, Denmark, where there are 24 mesocosms with 2 nutrients and 3 temperature treatments. Using bottle incubations, potential CH4 production and oxidation activity associated with sediment and plants were estimated for each mesocosm. Microbial analysis were run to quantify abundance of methanogenic archea and MOB through mcrA and pmoA gene amplification with quantitative polymerase chain reaction. Diffusive and ebullitive CH4 emissions were estimated from dissolved gas concentrations and bubble traps in each mesocosm. Results show that plants play an important direct and indirect role in shaping CH4 fluxes, but with different rates among species and treatments. Further results about how different activity of CH4 production/oxidation can shape emissions will be discussed
08:45 AM
Anaerobic or Aerobic? - Methane oxidation in the anoxic water column and sediments of stratified lakes (4993)
Primary Presenter: Moritz Lehmann, University of Basel (moritz.lehmann@unibas.ch)
A large fraction of the methane that is biogenically produced in lake sediments is oxidized by methane oxidation near the sediment-water interface and/or in the water column. Oxygen appears as the prime electron acceptor in lacustrine methane oxidation (MOx). Methane oxidizing microorganisms seem to thrive even under micro-oxic conditions, i.e., they may be responsible for significant methane turnover at extremely low, or “cryptic”, oxygen concentrations, for example in stratified lakes. Under anoxic condition, they may also use electron acceptors other than oxygen, yet our understanding of the modes and microbial players of true anaerobic methane oxidation (AOM) in freshwater environments is still incomplete. Here we showcase different scenarios in meromictic lakes where the combined lacustrine “aerobic/anaerobic methane filter” works efficiently. We demonstrate that strong MOx potentials can be maintained across redox transition zones, below which bacterial AOM is additionally fueled by nitrite/nitrate or other oxidants. We also show that sulfate-dependent archaeal AOM in lake sediments can be stimulated in the presence of Fe and Mn oxides through oxidation of reduced sulfur compounds. We argue that S- and N-dependent AOM may play a greatly underappreciated role in lakes, yet, the AOM regime and the key microorganisms involved may strongly depend on lake characteristics (e.g., water column dynamics) and/or other environmental controls.
09:00 AM
Sediment disturbance negatively impacts methanogen abundance but has variable effects on total methane emissions (5013)
Primary Presenter: Michael Booth, University of Cincinnati (michael.booth@uc.edu)
Methane emissions from aquatic ecosystems are increasingly recognized as substantial, yet variable, contribution to global greenhouse gas (GHG) emissions. In the literature, fish bioturbation has resulted in both reduced and enhanced emissions GHG emissions from sediments. To explore how the frequency of disturbance impacts the levels of methane emissions and the associated microbial communities, we quantified GHG emissions in sediment microcosms treated with various frequencies of mechanical disturbance, analogous to different levels of activity in benthic feeding fish. GHG emissions were largely driven by methane ebullition and were highest for the intermediate disturbance frequency (7 days). The lowest emissions were for the highest frequency treatment (3 days). While total microbial community structure did not differ among treatments, among methanogenic Archaea, we observed a shift towards greater relative abundance of a putatively oxygen-tolerant methanogenic phylotype (ca. Methanothrix paradoxum) in the highest frequency treatments and at depths impacted by disturbance (1 cm). ca. Methanothrix paradoxum demonstrated no change in abundance, suggesting disturbance negatively and preferentially impacted other methanogen populations. However, total methane emissions were not simply a function of methanogen populations and were likely impacted by the residence time of methane. Low frequency mechanical disruption resulted in lower methane ebullition compared to higher frequency treatments, which in turn resulted in reduced overall methane release, likely through enhanced methanotrophic activities. Overall, this work contributes to understanding how animal behavior may impact variation in GHG emissions and provides insight into how frequency of disturbance may impact emissions.
09:15 AM
Multiple sources of aerobic methane production in aquatic ecosystems include bacterial photosynthesis (5515)
Primary Presenter: J. Michael Beman, University of California, Merced (jmbeman@gmail.com)
Aquatic ecosystems are globally significant sources of the greenhouse gas methane to the atmosphere. Until recently, methane production was thought to be a strictly anaerobic process confined primarily to anoxic sediments. However, supersaturation of methane in oxygenated waters has been consistently observed in lakes and the ocean (termed the ‘methane paradox’), indicating that methane can be produced under oxic conditions through unclear mechanisms. Here we show aerobic methane production from multiple sources in freshwater incubation experiments under different treatments and based on biogeochemical, metagenomic, and metatranscriptomic data. We find that aerobic methane production appears to be associated with (bacterio)chlorophyll metabolism and photosynthesis, as well as with Proteobacterial degradation of methylphosphonate. Genes encoding pathways for putative photosynthetic- and methylphosphonate-based methane production also co-occur in Proteobacterial metagenome-assembled genomes. Our findings provide insight into known mechanisms of aerobic methane production, and suggest a potential co-occurring mechanism associated with bacterial photosynthesis in aquatic ecosystems.
09:30 AM
The role of hydrology and temperature in predicting methane in streams and rivers (5817)
Primary Presenter: Nora Casson, University of Winnipeg (n.casson@uwinnipeg.ca)
Fluvial ecosystems play an outsized role in the aquatic carbon cycle, and are especially important loci of methane (CH4) production, transport and processing. Methane concentrations and fluxes span a large range in streams and rivers, reflecting a complex set of environmental drivers, which operate at multiple spatial scales. Experimental and within-site studies have shown strong temperature dependence of CH4 emissions, yet global-scale syntheses have emphasized the need to consider the effect of temperature in the context of landscape drivers such as slope, soil carbon storage and local hydrology. In this study, we leveraged a new fluvial CH4 database (GRIMeDB) to evaluate the relative strength of temperature and stream discharge in predicting CH4 concentrations from 172 sites with more than 20 observations of gas concentration coupled to one or both of the predictor variables (nobs = 4887), using hierarchical linear models. We then used coupled spatial datasets to investigate the role of in situ and landscape-level predictors on the strength and direction of these relationships. Our results suggest that the global relationships with either discharge or temperature were weak (adjusted r2 = 0.02 and 0.001, respectively), and when site was included as a random effect, approximately 75% sites did not have a directional relationship between either temperature or discharge and CH4 concentration. These results emphasize the complex controls on river CH4 cycling and value of multi-year datasets in teasing apart interactive drivers of ecosystem-level patterns.
09:45 AM
Inland alkaline lakes: uncharted hotspots of carbon processing and GHG fluxes (7003)
Primary Presenter: Attila Szabo, Centre for Ecological Research (attila.szabo.ttk@gmail.com)
Inland aquatic systems, especially freshwater lakes, are known to contribute significantly to terrestrial greenhouse gas emissions through organic carbon processing. However, studies on carbon emission in saline, alkaline lakes are scarce, despite their total global water volume being comparable to that of freshwater lakes. Alkaline lakes are biogeochemically distinctive from freshwater habitats because of their high pH conditions. This leads to the direct conversion of dissolved atmospheric CO2 to bicarbonate and carbonate, causing CO2 removal from the atmosphere. However, alkaline lakes are also hotspots for terrestrial and macrophyte-derived organic carbon processing, which can result in greenhouse gas emissions. The FizzingSoda project aimed to gather seasonal gas emission data from alkaline lakes by conducting direct emission measurements on 12 distinct sites, alongside water chemical characterization and meta-omic investigations to understand the role of the resident microbiome in relation to atmospheric emissions. The results of the seasonal measurement campaigns showed that saline-alkaline lakes can substantially differ in their daily overall carbon trends. Carbon fluxes ranged from carbon dioxide sinks to substantial emitters (-181 mg C/m2/day to 3600 mg C/m2/day), with surprisingly high CH4 fluxes detected for all soda lakes. The FizzingSoda project findings highlight the need for more research on carbon cycling in alkaline lakes, given their significance in the global water system and potential contribution to greenhouse gas emissions and removal.
SS020A New Insights on The Methane and Nitrous Oxide Cycles from Freshwater and Marine Ecosystems Under Changing Climate
Description
Time: 8:30 AM
Date: 5/6/2023
Room: Auditorium Mallorca