Water retention and hydraulic conductivity characteristics are key input data in studies on soil water dynamics in the vadose zone. The most well‐known analytical functions to describe these characteristics are those given by Mualem and van Genuchten, where van Genuchten showed that both can be described by a limited set of shared parameters. Analytically, there are no restrictions on the range of pressure heads for which these characteristics can be used. Experience, however, has shown that for certain sets of parameters, the hydraulic conductivity cannot be computed accurately at low‐pressure heads. This is due to the accuracy of (double precision) floating point operations in computer code. It is shown that for low‐pressure heads, the Mualem function approaches a power function. An adapted version of the Mualem–van Genuchten (MvG) expression for the hydraulic conductivity is proposed: between saturation and a soil‐dependent critical pressure head, the classical Mualem expression is valid and below this critical pressure head a power function is used. The power function is defined such that it matches the Mualem value at the critical pressure head. No accuracy problems will occur when using the power function until the result approaches the smallest possible (double precision) floating point value that significantly differs from zero.
{"title":"Modified expression for hydraulic conductivity according to Mualem–van Genuchten to allow proper computations at low‐pressure heads","authors":"Marius Heinen","doi":"10.1002/vzj2.20279","DOIUrl":"https://doi.org/10.1002/vzj2.20279","url":null,"abstract":"Water retention and hydraulic conductivity characteristics are key input data in studies on soil water dynamics in the vadose zone. The most well‐known analytical functions to describe these characteristics are those given by Mualem and van Genuchten, where van Genuchten showed that both can be described by a limited set of shared parameters. Analytically, there are no restrictions on the range of pressure heads for which these characteristics can be used. Experience, however, has shown that for certain sets of parameters, the hydraulic conductivity cannot be computed accurately at low‐pressure heads. This is due to the accuracy of (double precision) floating point operations in computer code. It is shown that for low‐pressure heads, the Mualem function approaches a power function. An adapted version of the Mualem–van Genuchten (MvG) expression for the hydraulic conductivity is proposed: between saturation and a soil‐dependent critical pressure head, the classical Mualem expression is valid and below this critical pressure head a power function is used. The power function is defined such that it matches the Mualem value at the critical pressure head. No accuracy problems will occur when using the power function until the result approaches the smallest possible (double precision) floating point value that significantly differs from zero.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48366105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Schlegel, Jennifer Souza, S. Warix, R. MacNeille, E. Murray, A. Radke, S. Godsey, M. Seyfried, B. Finney, G. Flerchinger, K. Lohse
The Reynolds Creek Experimental Watershed (RCEW) and Critical Zone Observatory (CZO), located south of the western Snake River Plain in the Intermountain West of the United States, is the site of over 60 years of research aimed at understanding integrated earth processes in a semi‐arid climate to aid sustainable use of environmental resources. Meteoric water lines (MWLs) are used to interpret hydrologic processes, though equilibrium and nonequilibrium processes affect the linear function and can reveal seasonal and climatological effects, necessitating the development of local meteoric water lines (LMWLs). At RCEW‐CZO, an RCEW LMWL was developed using non‐volume‐weighted, orthogonal regression with assumed error in both predictor and response variables from several years of precipitation (2015, 2017, 2019, 2020, and 2021) primarily at three different elevations (1203, 1585, and 2043 m). As most precipitation is evaporated or intercepted by vegetation in the driest months, an RCEW LMWL for groundwater recharge (RCEW LMWL‐GWR) was also developed using precipitation from the wettest months (November through April). The RCEW LMWL (δ2H = 7.41 × δ18O – 3.09) is different from the RCEW LMWL‐GWR (δ2H = 8.21 × δ18O + 9.95) and compares favorably to other LMWLs developed for the region and climate. Comparative surface, spring, and subsurface water datasets within the RCEW‐CZO are more similar to precipitation during the wettest months than dry months, illustrating that some semi‐arid hydrologic systems may most appropriately be compared to MWLs developed from precipitation only from the wettest season.
{"title":"Seasonality and evaporation of water resources in Reynolds Creek Experimental Watershed and Critical Zone Observatory, Southwestern Idaho, USA","authors":"M. Schlegel, Jennifer Souza, S. Warix, R. MacNeille, E. Murray, A. Radke, S. Godsey, M. Seyfried, B. Finney, G. Flerchinger, K. Lohse","doi":"10.1002/vzj2.20278","DOIUrl":"https://doi.org/10.1002/vzj2.20278","url":null,"abstract":"The Reynolds Creek Experimental Watershed (RCEW) and Critical Zone Observatory (CZO), located south of the western Snake River Plain in the Intermountain West of the United States, is the site of over 60 years of research aimed at understanding integrated earth processes in a semi‐arid climate to aid sustainable use of environmental resources. Meteoric water lines (MWLs) are used to interpret hydrologic processes, though equilibrium and nonequilibrium processes affect the linear function and can reveal seasonal and climatological effects, necessitating the development of local meteoric water lines (LMWLs). At RCEW‐CZO, an RCEW LMWL was developed using non‐volume‐weighted, orthogonal regression with assumed error in both predictor and response variables from several years of precipitation (2015, 2017, 2019, 2020, and 2021) primarily at three different elevations (1203, 1585, and 2043 m). As most precipitation is evaporated or intercepted by vegetation in the driest months, an RCEW LMWL for groundwater recharge (RCEW LMWL‐GWR) was also developed using precipitation from the wettest months (November through April). The RCEW LMWL (δ2H = 7.41 × δ18O – 3.09) is different from the RCEW LMWL‐GWR (δ2H = 8.21 × δ18O + 9.95) and compares favorably to other LMWLs developed for the region and climate. Comparative surface, spring, and subsurface water datasets within the RCEW‐CZO are more similar to precipitation during the wettest months than dry months, illustrating that some semi‐arid hydrologic systems may most appropriately be compared to MWLs developed from precipitation only from the wettest season.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"1 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41582368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Bereswill, Hannah Gatz‐Miller, D. Su, C. Tötzke, N. Kardjilov, S. Oswald, K. Mayer
Oxygen (O2) availability in soils is vital for plant growth and productivity. The transport and consumption of O2 in the root zone is closely linked to soil moisture content, the spatial distribution of roots, as well as structure and heterogeneity of the surrounding soil. In this study, we measure three‐dimensional root system architecture and the spatiotemporal dynamics of soil moisture (θ) and O2 concentrations in the root zone of maize (Zea mays) via non‐invasive imaging, and then construct and parameterize a reactive transport model based on the experimental data. The combination of three non‐invasive imaging methods allowed for a direct comparison of simulation results with observations at high spatial and temporal resolution. In three different modeling scenarios, we investigated how the results obtained for different levels of conceptual complexity in the model were able to match measured θ and O2 concentration patterns. We found that the modeling scenario that considers heterogeneous soil structure and spatial variability of hydraulic parameters (permeability, porosity, and van Genuchten α and n), better reproduced the measured θ and O2 patterns relative to a simple model with a homogenous soil domain. The results from our combined imaging and modeling analysis reveal that experimental O2 and water dynamics can be reproduced quantitatively in a reactive transport model, and that O2 and water dynamics are best characterized when conditions unique to the specific system beyond the distribution of roots, such as soil structure and its effect on water saturation and macroscopic gas transport pathways, are considered.
{"title":"Coupling non‐invasive imaging and reactive transport modeling to investigate water and oxygen dynamics in the root zone","authors":"S. Bereswill, Hannah Gatz‐Miller, D. Su, C. Tötzke, N. Kardjilov, S. Oswald, K. Mayer","doi":"10.1002/vzj2.20268","DOIUrl":"https://doi.org/10.1002/vzj2.20268","url":null,"abstract":"Oxygen (O2) availability in soils is vital for plant growth and productivity. The transport and consumption of O2 in the root zone is closely linked to soil moisture content, the spatial distribution of roots, as well as structure and heterogeneity of the surrounding soil. In this study, we measure three‐dimensional root system architecture and the spatiotemporal dynamics of soil moisture (θ) and O2 concentrations in the root zone of maize (Zea mays) via non‐invasive imaging, and then construct and parameterize a reactive transport model based on the experimental data. The combination of three non‐invasive imaging methods allowed for a direct comparison of simulation results with observations at high spatial and temporal resolution. In three different modeling scenarios, we investigated how the results obtained for different levels of conceptual complexity in the model were able to match measured θ and O2 concentration patterns. We found that the modeling scenario that considers heterogeneous soil structure and spatial variability of hydraulic parameters (permeability, porosity, and van Genuchten α and n), better reproduced the measured θ and O2 patterns relative to a simple model with a homogenous soil domain. The results from our combined imaging and modeling analysis reveal that experimental O2 and water dynamics can be reproduced quantitatively in a reactive transport model, and that O2 and water dynamics are best characterized when conditions unique to the specific system beyond the distribution of roots, such as soil structure and its effect on water saturation and macroscopic gas transport pathways, are considered.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49112372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anne Imig, Lea Augustin, J. Groh, T. Pütz, Martin Elsner, F. Einsiedl, A. Rein
This study investigates the contamination potential of herbicides to groundwater with the help of numerical modeling (HYDRUS‐1D) and stable carbon isotopes for characterizing biodegradation. Four herbicides, metolachlor, terbuthylazine, prosulfuron, and nicosulfuron, were applied over a period of 4.5 years on two lysimeters located in Wielenbach, Germany, and monitored by lysimeter drainage. These lysimeters contained soil cores dominated by sandy gravel (Ly1) and clayey sandy silt (Ly2) and were both cropped with maize (Zea mays). In the preceding study, we characterized flow within the lysimeters by using stable water isotopes and unsaturated flow models. Building up on these findings, models were extended for describing reactive transport of the herbicides and investigating process contributions. At the end of the experiment, 0.9%–15.9% of the applied herbicides (up to 20.9% if including metabolites) were recovered by lysimeter drainage. Metabolite formation and accumulation was observed, and biodegradation was also indicated by small changes in carbon isotope signals (δ13C) between applied and leached herbicides. Model setups could describe the dynamics of herbicide concentrations in lysimeter drainage well. Concentration peaks in drainage were partly also linked with strong precipitation events, indicating preferential flow influence. The soil core with the coarser texture (Ly1) showed less herbicide leaching than the finer texture (Ly2), which can be explained by a larger mobile phase in Ly1. Overall, our approaches and findings contribute to the understanding of multi‐process herbicide transport in the vadose zone and leaching potentials to groundwater, where δ13C can provide valuable hints for microbial degradation.
{"title":"Fate of herbicides in cropped lysimeters: 2. Leaching of four maize herbicides considering different processes","authors":"Anne Imig, Lea Augustin, J. Groh, T. Pütz, Martin Elsner, F. Einsiedl, A. Rein","doi":"10.1002/vzj2.20275","DOIUrl":"https://doi.org/10.1002/vzj2.20275","url":null,"abstract":"This study investigates the contamination potential of herbicides to groundwater with the help of numerical modeling (HYDRUS‐1D) and stable carbon isotopes for characterizing biodegradation. Four herbicides, metolachlor, terbuthylazine, prosulfuron, and nicosulfuron, were applied over a period of 4.5 years on two lysimeters located in Wielenbach, Germany, and monitored by lysimeter drainage. These lysimeters contained soil cores dominated by sandy gravel (Ly1) and clayey sandy silt (Ly2) and were both cropped with maize (Zea mays). In the preceding study, we characterized flow within the lysimeters by using stable water isotopes and unsaturated flow models. Building up on these findings, models were extended for describing reactive transport of the herbicides and investigating process contributions. At the end of the experiment, 0.9%–15.9% of the applied herbicides (up to 20.9% if including metabolites) were recovered by lysimeter drainage. Metabolite formation and accumulation was observed, and biodegradation was also indicated by small changes in carbon isotope signals (δ13C) between applied and leached herbicides. Model setups could describe the dynamics of herbicide concentrations in lysimeter drainage well. Concentration peaks in drainage were partly also linked with strong precipitation events, indicating preferential flow influence. The soil core with the coarser texture (Ly1) showed less herbicide leaching than the finer texture (Ly2), which can be explained by a larger mobile phase in Ly1. Overall, our approaches and findings contribute to the understanding of multi‐process herbicide transport in the vadose zone and leaching potentials to groundwater, where δ13C can provide valuable hints for microbial degradation.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46923202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Vanderborght, D. Leitner, A. Schnepf, V. Couvreur, H. Vereecken, M. Javaux
{"title":"Combining root and soil hydraulics in macroscopic representations of root water uptake","authors":"J. Vanderborght, D. Leitner, A. Schnepf, V. Couvreur, H. Vereecken, M. Javaux","doi":"10.1002/vzj2.20273","DOIUrl":"https://doi.org/10.1002/vzj2.20273","url":null,"abstract":"","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49239488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Trochon, V. Bustillo, L. Caner, S. Pasquet, V. Suc, F. Granouillac, A. Probst, J. Probst, T. Tallec, M. Guiresse
Local waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot.
{"title":"Main water pathways in cultivated clayey calcisols in molassic hills in southwestern France: Toward spatialization of soil waterlogging","authors":"B. Trochon, V. Bustillo, L. Caner, S. Pasquet, V. Suc, F. Granouillac, A. Probst, J. Probst, T. Tallec, M. Guiresse","doi":"10.1002/vzj2.20272","DOIUrl":"https://doi.org/10.1002/vzj2.20272","url":null,"abstract":"Local waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"22 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42781597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Plant growth‐promoting rhizobacteria and other soil bacteria have the potential to improve soil hydro‐physical properties and processes through the production of extracellular polymeric substances (EPS). However, the mechanisms by which EPS mediates changes in soil properties and processes remain incompletely understood, partly due to variations in EPS composition produced under different environmental conditions. In this study, we investigated the influence of different bacterial traits on intrinsic soil properties and processes of evaporation and infiltration using sand treated with the wild‐type Bacillus subtilis variant (UD1022) and its two mutant variants, eps−$eps^{-}$ – tasA−$tasA^{-}$ and srf AC−$AC^{-}$ . The eps−$eps^{-}$ – tasA−$tasA^{-}$ mutant suppresses EPS production through alterations in the eps and tasA genes, while the srf AC−$AC^{-}$ mutant lacks the gene for surfactin production. Experimental results confirmed that the solution viscosity of the eps−$eps^{-}$ – tasA−$tasA^{-}$ mutant was the lowest and the solution surface tension of the srf AC−$AC^{-}$ mutant was the highest among the three tested bacteria strains. The distinct intrinsic properties of EPS produced by these bacterial strains resulted in varied hydro‐physical responses in the treated sand. Key influences included modifications in wettability, hydraulic decoupling (or mixed wettability), and aggregation, which collectively led to reduced evaporation rates and heterogeneous water distribution during infiltration in the bacteria‐treated sands. Our findings advance the understanding of the role bacterial EPS play in vadose zone hydrology and offer insights for the development of sustainable strategies for increasing water retention, supporting crop production in arid regions, and facilitating land restoration.
{"title":"Plant growth‐promoting rhizobacteria mediate soil hydro‐physical properties: An investigation with Bacillus subtilis and its mutants","authors":"Fatema Kaniz, Wenjuan Zheng, H. Bais, Yan Jin","doi":"10.1002/vzj2.20274","DOIUrl":"https://doi.org/10.1002/vzj2.20274","url":null,"abstract":"Plant growth‐promoting rhizobacteria and other soil bacteria have the potential to improve soil hydro‐physical properties and processes through the production of extracellular polymeric substances (EPS). However, the mechanisms by which EPS mediates changes in soil properties and processes remain incompletely understood, partly due to variations in EPS composition produced under different environmental conditions. In this study, we investigated the influence of different bacterial traits on intrinsic soil properties and processes of evaporation and infiltration using sand treated with the wild‐type Bacillus subtilis variant (UD1022) and its two mutant variants, eps−$eps^{-}$ – tasA−$tasA^{-}$ and srf AC−$AC^{-}$ . The eps−$eps^{-}$ – tasA−$tasA^{-}$ mutant suppresses EPS production through alterations in the eps and tasA genes, while the srf AC−$AC^{-}$ mutant lacks the gene for surfactin production. Experimental results confirmed that the solution viscosity of the eps−$eps^{-}$ – tasA−$tasA^{-}$ mutant was the lowest and the solution surface tension of the srf AC−$AC^{-}$ mutant was the highest among the three tested bacteria strains. The distinct intrinsic properties of EPS produced by these bacterial strains resulted in varied hydro‐physical responses in the treated sand. Key influences included modifications in wettability, hydraulic decoupling (or mixed wettability), and aggregation, which collectively led to reduced evaporation rates and heterogeneous water distribution during infiltration in the bacteria‐treated sands. Our findings advance the understanding of the role bacterial EPS play in vadose zone hydrology and offer insights for the development of sustainable strategies for increasing water retention, supporting crop production in arid regions, and facilitating land restoration.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46009903","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anne Imig, Lea Augustin, J. Groh, T. Pütz, Tiantian Zhou, F. Einsiedl, A. Rein
Understanding transport and fate processes in the subsurface is of fundamental importance to identify the leaching potentials of herbicides or other compounds to groundwater resources. HYDRUS‐1D was used to simulate water flow and solute transport in arable land lysimeters. Simulations were compared to observed drainage rates and stable water isotopes (δ18O) in the drainage. Four different model setups were investigated and statistically evaluated for their model performance to identify dominant processes for water flow characterization in the vadose zone under similar cultivation management and climatic conditions. The studied lysimeters contain soil cores dominated by sandy gravel (Ly1) and clayey sandy silt (Ly2), both cropped with maize located in Wielenbach, Germany. First, a single‐porosity setup was chosen. For Ly1, modeling results were satisfactory, but for Ly2, the damping observed in the isotope signature of the drainage could not be fully covered. By considering immobile water with a dual‐porosity setup for Ly2, model performance improved. This could be due to a higher fraction of fine pores in Ly2 available for water storage, leading to mixing processes of isotopically enriched summer precipitation and lighter winter water. Accounting for isotopic evaporation fractionation processes in both model setups did not lead to improved model performance. Consequentially, the difference in soil hydraulic properties between the two lysimeters seems to impact water flow processes. Knowledge of such differences is crucial to prevent contamination and mitigate potential risks to soil and groundwater.
{"title":"Fate of herbicides in cropped lysimeters: 1. Influence of different processes and model structure on vadose zone flow","authors":"Anne Imig, Lea Augustin, J. Groh, T. Pütz, Tiantian Zhou, F. Einsiedl, A. Rein","doi":"10.1002/vzj2.20265","DOIUrl":"https://doi.org/10.1002/vzj2.20265","url":null,"abstract":"Understanding transport and fate processes in the subsurface is of fundamental importance to identify the leaching potentials of herbicides or other compounds to groundwater resources. HYDRUS‐1D was used to simulate water flow and solute transport in arable land lysimeters. Simulations were compared to observed drainage rates and stable water isotopes (δ18O) in the drainage. Four different model setups were investigated and statistically evaluated for their model performance to identify dominant processes for water flow characterization in the vadose zone under similar cultivation management and climatic conditions. The studied lysimeters contain soil cores dominated by sandy gravel (Ly1) and clayey sandy silt (Ly2), both cropped with maize located in Wielenbach, Germany. First, a single‐porosity setup was chosen. For Ly1, modeling results were satisfactory, but for Ly2, the damping observed in the isotope signature of the drainage could not be fully covered. By considering immobile water with a dual‐porosity setup for Ly2, model performance improved. This could be due to a higher fraction of fine pores in Ly2 available for water storage, leading to mixing processes of isotopically enriched summer precipitation and lighter winter water. Accounting for isotopic evaporation fractionation processes in both model setups did not lead to improved model performance. Consequentially, the difference in soil hydraulic properties between the two lysimeters seems to impact water flow processes. Knowledge of such differences is crucial to prevent contamination and mitigate potential risks to soil and groundwater.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43289625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Leonardo Inforsato, S. Iden, W. Durner, A. Peters, Q. de Jong van Lier
Numerical modeling of soil water dynamics and storage is generally based on the Richards equation. Its solution requires knowledge of the soil hydraulic properties (SHP): the soil water retention function and the hydraulic conductivity function. To determine SHP, laboratory evaporation experiments are particularly popular because they provide data for both SHP functions. The evaluation by the simplified evaporation method (SEM) method, originally proposed by Schindler and subsequently improved by several authors, relies on linearization assumptions that allow for a relatively simple calculation scheme but result in biased conductivity data for some soils. The objective of this study is to propose and test an improved computational scheme for the hydraulic conductivity function. We present the new theory and show that it leads generally to higher accuracy of the conductivity function. The improvement is most pronounced for sandy soils and soil water pressure heads below −100 cm, where the original method provided data with bias.
{"title":"Improved calculation of soil hydraulic conductivity with the simplified evaporation method","authors":"Leonardo Inforsato, S. Iden, W. Durner, A. Peters, Q. de Jong van Lier","doi":"10.1002/vzj2.20267","DOIUrl":"https://doi.org/10.1002/vzj2.20267","url":null,"abstract":"Numerical modeling of soil water dynamics and storage is generally based on the Richards equation. Its solution requires knowledge of the soil hydraulic properties (SHP): the soil water retention function and the hydraulic conductivity function. To determine SHP, laboratory evaporation experiments are particularly popular because they provide data for both SHP functions. The evaluation by the simplified evaporation method (SEM) method, originally proposed by Schindler and subsequently improved by several authors, relies on linearization assumptions that allow for a relatively simple calculation scheme but result in biased conductivity data for some soils. The objective of this study is to propose and test an improved computational scheme for the hydraulic conductivity function. We present the new theory and show that it leads generally to higher accuracy of the conductivity function. The improvement is most pronounced for sandy soils and soil water pressure heads below −100 cm, where the original method provided data with bias.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44087763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Peat and other organic soils (e.g., organo‐mineral soils) show distinctive volume changes through desiccation and wetting. Important processes behind volume changes are shrinkage and swelling. There is a long history of studies on shrinkage which were conducted under different schemes for soil descriptions, nomenclatures and parameters, measurement approaches, and terminologies. To date, these studies have not been harmonized in order to compare or predict shrinkage from different soil properties, for example, bulk density or substrate composition. This, however, is necessary to prevent biases in the determination of volume‐based soil properties or for the interpretation of elevation measurements in peatlands, in order to predict carbon dioxide emissions or uptake caused by microbial decomposition or peat formation. This study gives a comprehensive overview of shrinkage studies carried out in the last 100 years. Terminology and approaches are systematically classified. In part I, the concepts for shrinkage characteristics, measurement methods, and model approaches are summarized. Part II is a meta‐analysis of shrinkage studies on peat and other organic soils amended by own measurement data obtained by a three‐dimensional structured light scanner. The results show that maximum shrinkage has a wide range from 11% to 93% and is strongly affected by common soil properties (botanical composition, degree of decomposition, soil organic carbon, and bulk density). Showing a stronger correlation, bulk density was a better predictor than soil organic carbon, but maximum shrinkage showed a large spread over all types of peat and other organic soils and ranges of bulk density and soil organic carbon.
{"title":"Reviewing and analyzing shrinkage of peat and other organic soils in relation to selected soil properties","authors":"Ronny Seidel, U. Dettmann, B. Tiemeyer","doi":"10.1002/vzj2.20264","DOIUrl":"https://doi.org/10.1002/vzj2.20264","url":null,"abstract":"Peat and other organic soils (e.g., organo‐mineral soils) show distinctive volume changes through desiccation and wetting. Important processes behind volume changes are shrinkage and swelling. There is a long history of studies on shrinkage which were conducted under different schemes for soil descriptions, nomenclatures and parameters, measurement approaches, and terminologies. To date, these studies have not been harmonized in order to compare or predict shrinkage from different soil properties, for example, bulk density or substrate composition. This, however, is necessary to prevent biases in the determination of volume‐based soil properties or for the interpretation of elevation measurements in peatlands, in order to predict carbon dioxide emissions or uptake caused by microbial decomposition or peat formation. This study gives a comprehensive overview of shrinkage studies carried out in the last 100 years. Terminology and approaches are systematically classified. In part I, the concepts for shrinkage characteristics, measurement methods, and model approaches are summarized. Part II is a meta‐analysis of shrinkage studies on peat and other organic soils amended by own measurement data obtained by a three‐dimensional structured light scanner. The results show that maximum shrinkage has a wide range from 11% to 93% and is strongly affected by common soil properties (botanical composition, degree of decomposition, soil organic carbon, and bulk density). Showing a stronger correlation, bulk density was a better predictor than soil organic carbon, but maximum shrinkage showed a large spread over all types of peat and other organic soils and ranges of bulk density and soil organic carbon.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":" ","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49599265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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