A pore-size classification for peat bogs derived from unsaturated hydraulic properties
In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these pr...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/21/6185/2017/hess-21-6185-2017.pdf |
| Summary: | In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone)
controls oxygen diffusion rates, redox state, and the turnover of organic
matter. Thus, variably saturated flow processes determine whether peatlands
act as sinks or sources of atmospheric carbon, and modelling these processes
is crucial to assess effects of changed environmental conditions on the
future development of these ecosystems. We show that the Richards equation
can be used to accurately describe the moisture dynamics under evaporative
conditions in variably saturated peat soil, encompassing the transition from
the topmost living moss layer to the decomposed peat as part of the vadose
zone. Soil hydraulic properties (SHP) were identified by inverse simulation
of evaporation experiments on samples from the entire acrotelm. To obtain
consistent descriptions of the observations, the traditional van
Genuchten–Mualem model was extended to account for non-capillary water
storage and flow. We found that the SHP of the uppermost moss layer reflect a
pore-size distribution (PSD) that combines three distinct pore systems of the
<i>Sphagnum</i> moss. For deeper samples, acrotelm pedogenesis changes the
shape of the SHP due to the collapse of inter-plant pores and an infill with
smaller particles. This leads to gradually more homogeneous and bi-modal PSDs
with increasing depth, which in turn can serve as a proxy for increasing
state of pedogenesis in peatlands. From this, we derive a nomenclature and
size classification for the pore spaces of <i>Sphagnum</i> mosses and
define inter-, intra-, and inner-plant pore spaces, with effective pore
diameters of > 300, 300–30, and 30–10 µm, respectively. |
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| ISSN: | 1027-5606 1607-7938 |