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Abstract:
Wetlands are one of the most significant natural sources of methane (CH4/ to the atmosphere. They emit CH4
because decomposition of soil organic matter in waterlogged
anoxic conditions produces CH4, in addition to carbon dioxide
(CO2/. Production of CH4 and how much of it escapes
to the atmosphere depend on a multitude of environmental
drivers. Models simulating the processes leading to CH4
emissions are thus needed for upscaling observations to estimate
present CH4 emissions and for producing scenarios
of future atmospheric CH4 concentrations. Aiming at a CH4
model that can be added to models describing peatland carbon
cycling, we composed a model called HIMMELI that
describes CH4 build-up in and emissions from peatland soils.
It is not a full peatland carbon cycle model but it requires
the rate of anoxic soil respiration as input. Driven by soil
temperature, leaf area index (LAI) of aerenchymatous peatland
vegetation, and water table depth (WTD), it simulates
the concentrations and transport of CH4, CO2, and oxygen
(O2/ in a layered one-dimensional peat column. Here, we
present the HIMMELI model structure and results of tests
on the model sensitivity to the input data and to the description
of the peat column (peat depth and layer thickness), and
demonstrate that HIMMELI outputs realistic fluxes by comparing
modeled and measured fluxes at two peatland sites. As
HIMMELI describes only the CH4-related processes, not the
full carbon cycle, our analysis revealed mechanisms and dependencies
that may remain hidden when testing CH4 models
connected to complete peatland carbon models, which is
usually the case. Our results indicated that (1) the model is
flexible and robust and thus suitable for different environments;
(2) the simulated CH4 emissions largely depend on the prescribed rate of anoxic respiration; (3) the sensitivity of diated
via the concentrations of dissolved gases, in particular,
the O2 concentrations that affect the CH4 production and
oxidation rates; (4) with given input respiration, the peat column
description does not significantly affect the simulated CH4 emissions in this model version.
