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| Titel |
Controls on peat hydraulic conductivity: bridging the gap between models and measurements |
| VerfasserIn |
Paul J. Morris, Andy J. Baird, Lisa R. Belyea |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110871
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| Publikation (Nr.) |
 EGU/EGU2015-11128.pdf |
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| Zusammenfassung |
| Peat hydraulic properties such as saturated hydraulic conductivity (Ksat) are variable in space
and time. A broadly accepted but poorly understood relationship between peat decomposition
and Ksat is highly influential on the behaviour of models of peatland development, but
existing data do not allow this relationship to be parameterised satisfactorily. Previous
empirical studies have typically used simple metrics of time-integrated decomposition such
as fibre content, von Post score or light transmission (humification) to predict Ksat. By
contrast, peatland development models represent the state of peat decomposition
as a more abstract fraction of remaining mass. As such, a gap exists between the
requirements of simulation models and the available empirical data – a gap that we seek to
address.
We collected fourteen shallow (~ 0.5 m long, 0.1 m diameter) peat cores from a
Swedish raised bog. Our sampling locations comprised two vegetation microhabitats,
hummocks and hollows (n = 7 for each), combined factorially with two locations – the
flat, treeless, central bog plateau (n = 8) and the treed, sloping bog margin (n =
6). In the laboratory we split the cores into 0.06 m depth intervals and measured
horizontal Ksat and dry bulk peat carbon to nitrogen concentration ratios (C:N).
Following a published method we used these C:N values to approximate the state of peat
decomposition (fractional mass remaining) for depth intervals deeper than ~ 0.1
m.
We used a step-up procedure to fit a linear mixed-effects (LME) model to the data, so as
to predict log10 (Ksat) from two continuous predictor variables, depth and our
C:N-derived approximation of fractional mass remaining; and two categorical predictors,
microhabitat (hummock, hollow) and location (central plateau, bog margin). The LME
model predicts that log10 (Ksat) declines linearly with increasing depth below
the surface (p < 0.001) and with increasing peat decomposition (p = 0.012); and
that it is greater in hummock peat than in hollow peat (p < 0.001). The categorical
distinction between central and marginal areas exerted no significant effect (p =
0.880).
Our LME model illustrates for the first time the nature of the relationship between Ksat
and fractional peat mass remaining, and suggests that changes are required to the form of the
algorithms used to predict Ksat in peatland development models. Specifically,
depth is usually ignored as a predictor variable, but in our study depth exerts a
strong control over Ksat independently of decomposition. Our findings also add
weight to the growing argument that the assumption of lower Ksat in hummocks
than in hollows – commonly adopted in modelling studies – should be revised. |
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