Changes in flow and transport patterns in fen peat following soil degradation

Liu, Haojie; Janssen, Manon; Lennartz, Bernd

doi:10.1111/ejss.12380

Cited by 51 publications

(73 citation statements)

References 38 publications

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“…With the beginning of decomposition of plant residues and soil compaction, a clear reduction of macroporosity occurred. With the further mineralization of organic matter, macroporosity remained almost constant because of the generation of secondary macropore space (e.g., root and worm channels; Liu & Lennartz, ; Liu et al, ). This sequence supports results for a single site investigated by Schwärzel et al ().…”

Section: Discussionsupporting

confidence: 93%

“…Generally, peatland drainage decreases total porosity, accompanied by a shift in pore size distribution (Rezanezhad et al, ; Wallor et al, ). Macropores are an important feature of pore structure in peat soils (Baird, ; Holden, ) and have a large effect on hydraulic properties (Baird, ; Liu, Janssen, & Lennartz, ). During peat decomposition and degradation processes, macroporosity decreases and microporosity increases (Rezanezhad et al, ; Silins & Rothwell, ), although a higher macroporosity could be observed in strongly decomposed peat than in less decomposed peat (Schindler, Behrendt, & Müller, ; Wallor et al, ).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hydraulic properties of peat soils along a bulk density gradient—A meta study

Liu

Lennartz

2018

Hydrological Processes

109

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Our understanding of hydraulic properties of peat soils is limited compared with that of mineral substrates. In this study, we aimed to deduce possible alterations of hydraulic properties of peat soils following degradation resulting from peat drainage and aeration. A data set of peat hydraulic properties (188 soil water retention curves [SWRCs], 71 unsaturated hydraulic conductivity curves [UHCs], and 256 saturated hydraulic conductivity [Ks] values) was assembled from the literature; the obtained data originated from peat samples with an organic matter (OM) content ranging from 23 to 97 wt% (weight percent; and according variation in bulk density) representing various degrees of peat degradation. The Mualem‐van Genuchten model was employed to describe the SWRCs and UHCs. The results show that the hydraulic parameters of peat soils vary over a wide range confirming the pronounced diversity of peat. Peat decomposition significantly modifies all hydraulic parameters. A bulk density of approximately 0.2 g cm−3 was identified as a critical threshold point; above and below this value, macroporosity and hydraulic parameters follow different functions with bulk density. Pedotransfer functions based on physical peat properties (e.g., bulk density and soil depth) separately computed for bog and fen peat have significantly lower mean square errors than functions obtained from the complete data set, which indicates that not only the status of peat decomposition but also the peat‐forming plants have a large effect on hydraulic properties. The SWRCs of samples with a bulk density of less than 0.2 g cm−3 could be grouped into two to five classes for each peat type (botanical composition). The remaining SWRCs originating from samples with a bulk density of larger than 0.2 g cm−3 could be classified into one group. The Mualem‐van Genuchten parameter values of α can be used to estimate Ks if no Ks data are available. In conclusion, the derived pedotransfer functions provide a solid instrument to derive hydraulic parameter values from easily measurable quantities; however, additional research is required to reduce uncertainty.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Hydraulic properties of peat soils along a bulk density gradient—A meta study

Liu

Lennartz

2018

Hydrological Processes

109

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“…Additionally to the K s tests, a salt tracer test combined with a determination of the DOC content was carried out for three soil columns of Peat F1 (relating to Hypothesis 3). They were placed in a flow‐through device connected to a peristaltic pump (an illustration of the set‐up can be found in Liu, Janssen, and Lennartz, ) and were saturated for 1 day with water with an EC of 0.7 mS cm −1 . Subsequently, two pore volumes with the same EC were pumped through (0.7 ml min −1 ).…”

Section: Methodsmentioning

confidence: 99%

Impact of the water salinity on the hydraulic conductivity of fen peat

Gosch

Janssen

Lennartz

2018

Hydrological Processes

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Coastal peatlands represent an interface between marine and terrestrial ecosystems; their hydrology is affected by salt and fresh water inflow alike. Previous studies on bog peat have shown that pore water salinity can have an impact on the saturated hydraulic conductivity (Ks) of peat because of chemical pore dilation effects. In this study, we aimed at quantifying the impact of higher salinities (up to 3.5% NaCl) on Ks of fen peat. Two experiments employing a constant‐head upward‐flow permeameter and differing in measurement and salinity change duration were conducted. Additionally, a third experiment to determine the impact of water salinity on the release of dissolved organic carbon (DOC) of the studied peat type was carried out. The results show a decrease of Ks with time, which does not depend on the water salinity but is differently shaped for different peat types. We assume pore clogging due to a conglomerate of physical, chemical, and biological processes, which rather depend on water movement rate and time than on water salinity. However, an increased water salinity did increase the DOC release. We conclude that salinity‐dependent behaviour of Ks is a function of peat chemistry and that for some peat types, salinity may only affect the DOC release without having a pronounced impact on water flow.

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“…Cl − MIM 9.81 × 10 −2 6.66 × 10 −2 fixed to 1 1.00 100 a 0.9 0.032 −406 (91 %) (19 %) (1510 %) (N/E) (N/E) CDE 9.79 × 10 −2 6.66 × 10 −2 fixed to 1 n/a n/a n/a 0.032 −408 (1 %) (7 %) Na + CDE fixed fixed 2.65 n/a n/a n/a 0.145 −229 (3 %) OSA fixed fixed 3.07 n/a 0.5 b 1.12 × 10 −3 0.024 −443 in laboratory studies that breakthrough experiments on peat need to be described by the MIM (Hoag and Price, 1997;Rezanezhad et al, 2012;Liu et al, 2016;Rezanezhad et al, 2017;Thiemeyer et al, 2017). Additionally, this finding is reflected in the fact that a multimodal retention curve was not observable, which would have been indicative for a twodomain flow of solute transport.…”

Section: Solute Transport Model Selectionmentioning

confidence: 99%

Saturated and unsaturated salt transport in peat from a constructed fen

Simhayov¹,

Weber²,

Price³

2017

Preprint

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Abstract. The underlying processes governing solute transport in peat from an experimentally constructed fen peatland were analyzed by performing saturated and unsaturated solute breakthrough experiments using Na + and Cl − as reactive and non-reactive solutes, respectively. We tested the performance of three solute transport models, including the classical equilibrium convection-dispersion equation (CDE), a chemical non-equilibrium one-site adsorption model (OSA) and a model to account for physical non-equilibrium, the mobile-immobile (MIM) phases. The selection was motivated by the fact that the applicability of the MIM in peat soils finds a wide consensus. However, results from inverse modeling and a robust statistical evaluation of this peat provide evidence that the measured breakthrough of the conservative tracer, Cl − , could be simulated well using the CDE. Furthermore, the very high Damköhler number (which approaches infinity) suggests instantaneous equilibration between the mobile and immobile phases underscoring the redundancy of the MIM approach for this particular peat. Scanning electron microscope images of the peat show the typical multi-pore size distribution structures have been homogenized sufficiently by decomposition, such that physical non-equilibrium solute transport no longer governs the transport process. This result is corroborated by the fact the soil hydraulic properties were adequately described using a unimodal van Genuchten-Mualem model between saturation and a pressure head of ∼ −1000 cm of water. Hence, MIM was not the most suitable choice, and the long tailing of the Na + breakthrough curve was caused by chemical non-equilibrium. Successful description was possible using the OSA model. To test our results for the unsaturated case, we conducted an unsaturated steady-state evaporation experiment to drive Na + and Cl − transport. Using the parameterized transport models from the saturated experiments, we could numerically simulate the unsaturated transport using Hydrus-1-D. The simulation showed a good prediction of observed values, confirming the suitability of the parameters for use in a slightly unsaturated transport simulation. The findings improve the understanding of solute redistribution in the constructed fen and imply that MIM should not be automatically assumed for solute transport in peat but rather should be evidence based.

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Changes in flow and transport patterns in fen peat following soil degradation

Cited by 51 publications

References 38 publications

Hydraulic properties of peat soils along a bulk density gradient—A meta study

Hydraulic properties of peat soils along a bulk density gradient—A meta study

Impact of the water salinity on the hydraulic conductivity of fen peat

Saturated and unsaturated salt transport in peat from a constructed fen

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