The Role of Pore Structure on Nitrate Reduction in Peat Soil: A Physical Characterization of Pore Distribution and Solute Transport

Rezanezhad, Fereidoun; Kleimeier, Christian; Milojevic, Tatjana; Liu, Haojie; Weber, Tobias K. D.; Cappellen, Philippe Van; Lennartz, Bernd

doi:10.1007/s13157-017-0930-4

Cited by 19 publications

(23 citation statements)

References 47 publications

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“…It is a typical drained peatland in northern Germany with a highly degraded peat top soil. The soil carbon content of the top soil is 33.0% by weight [15,26]. The uppermost highly degraded peat was removed (0-20 cm depths) and transported to a greenhouse at the University of Rostock for the mesocosm experiment.…”

Section: Field Site and Samplingmentioning

confidence: 99%

Nitrate Attenuation in Degraded Peat Soil-Based Constructed Wetlands

Kleimeier

Liu

Rezanezhad

et al. 2018

Water

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Constructed wetlands (CWs) provide favorable conditions for removing nitrate from polluted agricultural runoff via heterotrophic denitrification. Although the general operability of CWs has been shown in previous studies, the suitability of peat soils as a bed medium for a vertical flow through a system for nitrate attenuation has not been proven to date. In this study, a mesocosm experiment was conducted under continuous flow with conditions aiming to quantify nitrate (NO 3 −) removal efficiency in degraded peat soils. Input solution of NO 3 − was supplied at three different concentrations (65, 100, and 150 mg/L). Pore water samples were collected at different depths and analyzed for NO 3 − , pH, and dissolved N 2 O concentrations. The redox potential (Eh) was registered at different depths. The results showed that the median NO 3-N removal rate was 1.20 g/(m 2 •day) and the median removal efficiency was calculated as 63.5%. The nitrate removal efficiency was affected by the NO 3 − supply load, flow rate, and environmental boundary conditions. A higher NO 3 − removal efficiency was observed at an input NO 3 − concentration of 100 mg/L, a lower flow rate, and higher temperature. The results of pore water pH and NO 3 − and N 2 O levels from the bottom of the mesocosm suggest that N 2 is the dominant denitrification product. Thus, degraded peat soils showed the potential to serve as a substrate for the clean-up of nitrate-laden agricultural runoff.

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Section: Field Site and Samplingmentioning

confidence: 99%

Nitrate Attenuation in Degraded Peat Soil-Based Constructed Wetlands

Kleimeier

Liu

Rezanezhad

et al. 2018

Water

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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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“…To determine the peat soil hydraulic properties, we conducted transient evaporation experiments (Schindler, 1980;Peters et al, 2015;Weber et al, 2017a, b) for the retention properties, supplemented with tension disk experiments (Klute and Dirksen, 1986;McCarter et al, 2017). Tension disk experiments are considered to be a more reliable method to determine the unsaturated hydraulic conductivity in the wet range, because transient evaporation experiments contain limited information at pressure heads between 0 and −60 cm for the unsaturated hydraulic conductivity curve (Peters and Durner, 2008).…”

Section: Soil Hydraulic Propertiesmentioning

confidence: 99%

“…Following the traditional approach for solute transport parameterization in peat (Rezanezhad et al, 2012(Rezanezhad et al, , 2017, we initially assumed the MIM model and compared it with the performance of the CDE for the non-reactive solute. For Na + , transport parameters were additionally estimated with a one-site chemical adsorption model.…”

Section: Solute Transport Modelsmentioning

confidence: 99%

Section: Solute Modelmentioning

confidence: 99%

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Anonymous

2017

Preprint

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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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The Role of Pore Structure on Nitrate Reduction in Peat Soil: A Physical Characterization of Pore Distribution and Solute Transport

Cited by 19 publications

References 47 publications

Nitrate Attenuation in Degraded Peat Soil-Based Constructed Wetlands

Nitrate Attenuation in Degraded Peat Soil-Based Constructed Wetlands

Saturated and unsaturated salt transport in peat from a constructed fen

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