Organic matter and sediment properties determine in-lake variability of sediment CO<sub>2</sub> and CH<sub>4</sub> production and emissions of a small and shallow lake
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Published:2020-10-20
Issue:20
Volume:17
Page:5057-5078
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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:
Praetzel Leandra Stephanie EmiliaORCID, Plenter Nora, Schilling Sabrina, Schmiedeskamp MarcelORCID, Broll Gabriele, Knorr Klaus-HolgerORCID
Abstract
Abstract. Inland waters, particularly small and shallow lakes, are significant sources
of carbon dioxide (CO2) and methane (CH4) to the atmosphere.
However, the spatial in-lake heterogeneity of CO2 and CH4
production processes and their drivers in the sediment remain poorly
studied. We measured potential CO2 and CH4 production in slurry
incubations from 12 sites within the small and shallow crater lake Windsborn
in Germany, as well as fluxes at the water–atmosphere interface of intact
sediment core incubations from four sites. Production rates were highly
variable and ranged from 7.2 to 38.5 µmol CO2 gC−1 d−1 and from 5.4 to 33.5 µmol CH4 gC−1 d−1. Fluxes ranged
from 4.5 to 26.9 mmol CO2 m−2 d−1 and from 0 to 9.8 mmol
CH4 m−2 d−1. Both CO2 and CH4 production rates and
the CH4 fluxes exhibited a significant and negative correlation (p<0.05, ρ<−0.6) with a prevalence of recalcitrant
organic matter (OM) compounds in the sediment as identified by
Fourier-transformed infrared spectroscopy. The carbon / nitrogen ratio
exhibited a significant negative correlation (p<0.01, ρ=-0.88)
with CH4 fluxes but not with production rates or CO2 fluxes.
The availability of inorganic (nitrate, sulfate, ferric iron) and organic (humic
acids) electron acceptors failed to explain differences in CH4
production rates, assuming a competitive suppression, but observed
non-methanogenic CO2 production could be explained up to 91 % by
prevalent electron acceptors. We did not find clear relationships between OM
quality, the thermodynamics of methanogenic pathways (acetoclastic vs.
hydrogenotrophic) and electron-accepting capacity of the OM. Differences in
CH4 fluxes were interestingly to a large part explained by grain size
distribution (p<0.05, ρ=±0.65). Surprisingly though,
sediment gas storage, potential production rates and water–atmosphere fluxes
were decoupled from each other and did not show any correlations. Our
results show that within a small lake, sediment CO2 and CH4
production shows significant spatial variability which is mainly driven by
spatial differences in the degradability of the sediment OM. We highlight
that studies on production rates and sediment quality need to be interpreted
with care, though, in terms of deducing emission rates and patterns as
approaches based on production rates only neglect physical sediment
properties and production and oxidation processes in the water column as
major controls on actual emissions.
Funder
Deutsche Forschungsgemeinschaft
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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