High-resolution vertical biogeochemical profiles in the hyporheic zone reveal insights into microbial methane cycling
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Published:2022-09-21
Issue:18
Volume:19
Page:4551-4569
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Michaelis Tamara, Wunderlich AnjaORCID, Coskun Ömer K., Orsi William, Baumann ThomasORCID, Einsiedl Florian
Abstract
Abstract. Facing the challenges of climate change, policy making
relies on sound greenhouse gas (GHG) budgets. Rivers and streams emit large
quantities of the potent GHG methane (CH4), but their global impact on
atmospheric CH4 concentrations is highly uncertain. In situ data from
the hyporheic zone (HZ), where most CH4 is produced and some of it can
be oxidized to CO2, are lacking for an accurate description of CH4
production and consumption in streams. To address this, we recorded
high-resolution depth-resolved geochemical profiles at five different
locations in the stream bed of the river Moosach, southern Germany.
Specifically, we measured pore-water concentrations and stable carbon
isotopes (δ13C) of dissolved CH4 as well as relevant
electron acceptors for oxidation with a 1 cm vertical depth resolution.
Findings were interpreted with the help of a numerical model, and 16S rRNA
gene analyses added information on the microbial community at one of the
locations. Our data confirm with pore-water CH4 concentrations of up
to 1000 µmol L−1 that large quantities of CH4 are produced in
the HZ. Stable isotope measurements of CH4 suggest that
hydrogenotrophic methanogenesis represents a dominant pathway for CH4
production in the HZ of the river Moosach, while a relatively high abundance of
a novel group of methanogenic archaea, the Candidatus “Methanomethyliales” (phylum
Candidatus “Verstraetearchaeota”), indicate that CH4 production through H2-dependent methylotrophic methanogenesis might also be an important CH4
source. Combined isotopic and modeling results clearly implied CH4
oxidation processes at one of the sampled locations, but due to the steep
chemical gradients and the close proximity of the oxygen and nitrate
reduction zones, no single electron acceptor for this process could be
identified. Nevertheless, the numerical modeling results showed
potential not only for aerobic CH4 oxidation but also for anaerobic oxidation
of CH4 coupled to denitrification. In addition, the nitrate–methane
transition zone was characterized by an increased relative abundance of
microbial groups (Crenothrix, NC10) known to mediate nitrate and nitrite-dependent
methane oxidation in the hyporheic zone. This study demonstrates substantial CH4 production in hyporheic
sediments, a potential for aerobic and anaerobic CH4 oxidation, and
underlines the high spatiotemporal variability in this habitat.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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