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| Titel |
Modelling effects of seasonal variation in water table depth on net ecosystem CO2 exchange of a tropical peatland |
| VerfasserIn |
M. Mezbahuddin, R. F. Grant, T. Hirano |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 3 ; Nr. 11, no. 3 (2014-02-03), S.577-599 |
| Datensatznummer |
250117184
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| Publikation (Nr.) |
 copernicus.org/bg-11-577-2014.pdf |
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| Zusammenfassung |
| Seasonal variation in water table depth (WTD) determines the balance between
aggradation and degradation of tropical peatlands. Longer dry seasons
together with human interventions (e.g. drainage) can cause WTD drawdowns
making tropical peatland C storage highly vulnerable. Better predictive
capacity for effects of WTD on net CO2 exchange is thus essential to
guide conservation of tropical peat deposits. Mathematical modelling of basic
eco-hydrological processes under site-specific conditions can provide such
predictive capacity. We hereby deploy a process-based mathematical model
ecosys to study effects of seasonal variation in WTD on net
ecosystem productivity (NEP) of a drainage affected tropical peat swamp
forest at Palangkaraya, Indonesia. Simulated NEP suggested that the peatland
was a C source (NEP ~ −2 g C m−2 d−1, where a negative
sign represents a C source and a positive sign a C sink) during rainy seasons
with shallow WTD, C neutral or a small sink (NEP
~ +1 g C m−2 d−1) during early dry seasons with
intermediate WTD and a substantial C source (NEP
~ −4 g C m−2 d−1) during late dry seasons with deep WTD
from 2002 to 2005. These values were corroborated by regressions
(P < 0.0001) of hourly modelled vs. eddy covariance (EC) net
ecosystem CO2 fluxes which yielded R2 > 0.8,
intercepts approaching 0 and slopes approaching 1. We also simulated a
gradual increase in annual NEP from 2002 (−609 g C m−2) to 2005
(−373 g C m−2) with decreasing WTD which was attributed to declines
in duration and intensity of dry seasons following the El Niño event of
2002. This increase in modelled NEP was corroborated by EC-gap filled annual
NEP estimates. Our modelling hypotheses suggested that (1) poor aeration in
wet soils during shallow WTD caused slow nutrient (predominantly phosphorus)
mineralization and consequent slow plant nutrient uptake that suppressed
gross primary productivity (GPP) and hence NEP (2) better soil aeration
during intermediate WTD enhanced nutrient mineralization and hence plant
nutrient uptake, GPP and NEP and (3) deep WTD suppressed NEP through a
combination of reduced GPP due to plant water stress and increased ecosystem
respiration (Re) from enhanced deeper peat aeration. These WTD
effects on NEP were modelled from basic eco-hydrological processes including
microbial and root oxidation-reduction reactions driven by soil and root
O2 transport and uptake which in turn drove soil and plant carbon,
nitrogen and phosphorus transformations within a soil-plant-atmosphere water
transfer scheme driven by water potential gradients. Including these
processes in ecosystem models should therefore provide an improved predictive
capacity for WTD management programs intended to reduce tropical peat
degradation. |
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