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| Titel |
Transport, anoxia and energy control on anaerobic respiration and methanogenesis in anoxic peat soils |
| VerfasserIn |
Simona Bonaiuti, Christian Blodau, Klaus-Holger Knorr |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144633
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| Publikation (Nr.) |
 EGU/EGU2017-8483.pdf |
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| Zusammenfassung |
| In deep and permanently water saturated peat deposits, extremely low diffusive transport and
concomitant build-up of metabolic end-products, i.e of dissolved inorganic carbon
(DIC) and methane (CH4), have been found to slow-down anaerobic respiration
and methanogenesis. Such accumulation of DIC and CH4 lowers the Gibbs free
energy yield of terminal respiration and methanogenesis, which can inhibit the
course of anaerobic metabolic processes. In particular, this affects terminal steps of
the breakdown of organic carbon (C), such as methanogenesis, acetogenesis and
fermentation processes, which occur near thermodynamic minimum energy thresholds.
This effect is thus of critical importance for the long-term C sequestration, as the
slow-down of decomposition ultimately regulates the long-term fate of C in deep
peat deposits. The exact controls of this observed slow-down of organic matter
mineralization are not yet fully understood. Moreover, altered patterns of water or
gas transport due to predicted changes in climate may affect these controls in peat
soils.
Therefore, the aim of this study was to investigate how burial of peat leads to an
inactivation of anaerobic decomposition and to investigate the effects of advective water
transport and persistently anoxic conditions on anaerobic decomposition, temporal evolution
of thermodynamic energy yields to methanogenesis and methanogenic pathways. To this end,
we conducted a column experiment with homogenized, ombrotrophic peat over a period of
300 days at 20˚ C. We tested i) a control treatment under diffusive transport only, ii) an
advective flow treatment with a flow of 10 mm d−1, and iv) an anoxic treatment to
evaluate changes in decomposition in absence of oxygen in the unsaturated zone of the
cores.
A slow-down of anaerobic respiration and methanogenesis generally set in at
larger depths after 150 days at CH4 concentrations of 0.6-0.9 mmol L−1 and DIC
concentrations of 6-12 mmol L−1. This effect occurred at higher concentration levels and
faster than previously observed. Advective water transport effectively extended
the zone of methanogenesis down to 40 cm depth until inhibiting conditions were
reached, although net turnover at greater depths was not affected. Strictly anoxic
conditions in the unsaturated zone, where diffusive transport is high, had little effect on
accelerating anaerobic decomposition. The slow-down of net production rates of CO2 and
CH4 agreed well with the decline over time of Gibbs free energies available to
methanogenesis, supporting a thermodynamic constraint on decomposition in deeper peat
deposits.
Keywords: Peatlands; Anaerobic decomposition; Methanogenesis; Production rates;
Advection; Anoxia; Thermodynamic calculations. |
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