Daniel Murungi Kironde Kibirige, Shaeden Gokool, Zama Nosihle Mkhize
Abstract Soil moisture (SM) is a fundamental constituent of the terrestrial environment and the hydrological cycle. Owing to its significant influence on catchment hydrological responses, it can be utilized as an indicator of floods and droughts to aid early warning systems. This study aimed to develop a field‐scale method to estimate SM using parametric and machine learning‐based methods to compare whether advanced artificial intelligence methods can give similar results as traditional methods. Considering this, monthly observed SM data (from the top 10 cm), environmental covariates, and remotely sensed data from March 2019 to July 2021 for the Cathedral Peak Research Catchments VI and IX in South Africa were obtained. From the 241 observations obtained across 12 sites, 160 (∼66%) were used for model training, while the remaining 81 (∼34%) were used for model testing. Employing 10‐fold cross‐validation, the individual machine learning models (viz., support vector machine [SVM], random forest (RF), k‐nearest neighbor, classification and regression trees [Rpart], and generalized linear model) displayed a satisfactory performance ( R 2 = 0.52–0.79; root mean square error = 3.79–5.80). In the validation phase, the RF model displayed a superior performance, followed by the SVM. Subsequent SM estimation using the hybrid model produced satisfactory results in training ( R 2 = 0.90) and testing ( R 2 = 0.45). The results obtained from this study can aid in predicting SM variations in catchments with limited monitoring. Furthermore, this model can be applied in drought monitoring, forecasting, and informing agricultural management practices.
{"title":"Estimation of soil moisture using environmental covariates and machine learning algorithms in Cathedral Peak Catchment, South Africa","authors":"Daniel Murungi Kironde Kibirige, Shaeden Gokool, Zama Nosihle Mkhize","doi":"10.1002/vzj2.20289","DOIUrl":"https://doi.org/10.1002/vzj2.20289","url":null,"abstract":"Abstract Soil moisture (SM) is a fundamental constituent of the terrestrial environment and the hydrological cycle. Owing to its significant influence on catchment hydrological responses, it can be utilized as an indicator of floods and droughts to aid early warning systems. This study aimed to develop a field‐scale method to estimate SM using parametric and machine learning‐based methods to compare whether advanced artificial intelligence methods can give similar results as traditional methods. Considering this, monthly observed SM data (from the top 10 cm), environmental covariates, and remotely sensed data from March 2019 to July 2021 for the Cathedral Peak Research Catchments VI and IX in South Africa were obtained. From the 241 observations obtained across 12 sites, 160 (∼66%) were used for model training, while the remaining 81 (∼34%) were used for model testing. Employing 10‐fold cross‐validation, the individual machine learning models (viz., support vector machine [SVM], random forest (RF), k‐nearest neighbor, classification and regression trees [Rpart], and generalized linear model) displayed a satisfactory performance ( R 2 = 0.52–0.79; root mean square error = 3.79–5.80). In the validation phase, the RF model displayed a superior performance, followed by the SVM. Subsequent SM estimation using the hybrid model produced satisfactory results in training ( R 2 = 0.90) and testing ( R 2 = 0.45). The results obtained from this study can aid in predicting SM variations in catchments with limited monitoring. Furthermore, this model can be applied in drought monitoring, forecasting, and informing agricultural management practices.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"60 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135112917","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}
Abstract With reference to a more compacted and less conductive upper soil layer overlying a less compacted and more conductive subsoil, a simple three‐dimensional (3D) infiltration run is expected to yield more representative results of the upper layer than the subsoil. However, there is the need to quantitatively establish what is meant by more representativeness. At this aim, numerically simulated infiltration was investigated for a theoretically unconfined process under a null ponded head of water (d0H0 setup, with d = depth of ring insertion and H = ponded depth of water) and a practical Beerkan run (d1H1 setup, d = H = 1 cm). The considered layered soils differed by both the layering degree (from weak to strong; subsoil more conductive than the upper soil layer by 2.3–32.4 times, depending on the layering degree) and the thickness of the upper soil layer (0.5–3 cm). It was confirmed that water infiltration should be expected to be more representative of the upper soil layer when this layer is the less permeable since, for a 2‐h experiment, the instantaneous infiltration rates for the layered soil were 1.0–2.1 times greater than those of the homogeneous low‐permeable soil and 1.3–20.7 smaller than those of the homogeneous coarser soil that constituted the subsoil. Similarity with the homogeneous fine soil increased as expected as the upper layer became thicker. For a weak layering condition, the layered soil yielded an intermediate infiltration as compared with that of the two homogeneous soils forming the layered system. For a strong layering degree, the layered soil was more similar to the homogeneous fine soil than to the homogeneous coarse soil. Using the practical setup instead of the theoretical one should have a small to moderate effect on the instantaneous infiltration rates since all the calculated percentage differences between the d1H1 and d0H0 setups fell into the relatively narrow range of −18.8% to +17.4%. A sequential analysis procedure appeared usable to detect layering conditions but with some modifications as compared with the originally proposed procedure. The practical setup enhanced the possibility to recognize the time at which the characteristics of the subsoil start to influence the infiltration process. In conclusion, this investigation contributed to better interpret both the theoretical and the practically established 3D infiltration process in a soil composed of a less conductive upper soil layer overlying a more conductive subsoil and it also demonstrated that modifying the recently proposed sequential analysis procedure only using infiltration data could be advisable to determine the time when layering starts to influence the process.
考虑到较密实但导电性较差的上层土壤覆盖在较密实但导电性较好的底土上，简单的三维(3D)入渗运行有望获得比底土更具代表性的上层土壤结果。但是，需要从数量上确定什么是更具代表性。为此，研究了零蓄水池水头(d0H0设置，d =环插入深度，H =蓄水池深度)和实际贝尔坎运行(d1H1设置，d = H = 1 cm)下的理论无约束入渗过程的数值模拟。所考虑的层状土的分层程度不同(从弱到强;下层土壤的导电性是上层土壤的2.3-32.4倍(取决于分层程度)和上层土壤的厚度(0.5 - 3cm)。当上层土壤渗透性较差时，水的入渗应该更能代表上层土壤，因为在2小时的实验中，层状土壤的瞬时入渗速率是均匀低渗透性土壤的1.0-2.1倍，比构成下层土壤的均匀粗质土壤的瞬时入渗速率小1.3-20.7倍。与均匀细土相似度随上层厚度的增加而增加。在弱分层条件下，与形成分层系统的两种均质土壤相比，分层土壤的入渗中等。分层程度较强时，层状土更接近均质细土而非均质粗土。使用实际设置而不是理论设置应该对瞬时入渗率产生小到中等的影响，因为d1H1和d0H0设置之间的所有计算百分比差异都落在−18.8%至+17.4%的相对狭窄的范围内。序列分析程序似乎可用于检测分层条件，但与最初提出的程序相比有一些修改。实际设置增强了识别底土特性开始影响入渗过程的时间的可能性。总之，本研究有助于更好地解释由导电性较差的上层土壤覆盖在导电性较高的下层土壤上的土壤中理论和实际建立的三维入渗过程，并且还表明，修改最近提出的仅使用入渗数据的顺序分析程序可能是可取的，以确定分层开始影响过程的时间。
{"title":"A numerical test of soil layering effects on theoretical and practical Beerkan infiltration runs","authors":"Vincenzo Bagarello, Massimo Iovino, Jianbin Lai","doi":"10.1002/vzj2.20283","DOIUrl":"https://doi.org/10.1002/vzj2.20283","url":null,"abstract":"Abstract With reference to a more compacted and less conductive upper soil layer overlying a less compacted and more conductive subsoil, a simple three‐dimensional (3D) infiltration run is expected to yield more representative results of the upper layer than the subsoil. However, there is the need to quantitatively establish what is meant by more representativeness. At this aim, numerically simulated infiltration was investigated for a theoretically unconfined process under a null ponded head of water (d0H0 setup, with d = depth of ring insertion and H = ponded depth of water) and a practical Beerkan run (d1H1 setup, d = H = 1 cm). The considered layered soils differed by both the layering degree (from weak to strong; subsoil more conductive than the upper soil layer by 2.3–32.4 times, depending on the layering degree) and the thickness of the upper soil layer (0.5–3 cm). It was confirmed that water infiltration should be expected to be more representative of the upper soil layer when this layer is the less permeable since, for a 2‐h experiment, the instantaneous infiltration rates for the layered soil were 1.0–2.1 times greater than those of the homogeneous low‐permeable soil and 1.3–20.7 smaller than those of the homogeneous coarser soil that constituted the subsoil. Similarity with the homogeneous fine soil increased as expected as the upper layer became thicker. For a weak layering condition, the layered soil yielded an intermediate infiltration as compared with that of the two homogeneous soils forming the layered system. For a strong layering degree, the layered soil was more similar to the homogeneous fine soil than to the homogeneous coarse soil. Using the practical setup instead of the theoretical one should have a small to moderate effect on the instantaneous infiltration rates since all the calculated percentage differences between the d1H1 and d0H0 setups fell into the relatively narrow range of −18.8% to +17.4%. A sequential analysis procedure appeared usable to detect layering conditions but with some modifications as compared with the originally proposed procedure. The practical setup enhanced the possibility to recognize the time at which the characteristics of the subsoil start to influence the infiltration process. In conclusion, this investigation contributed to better interpret both the theoretical and the practically established 3D infiltration process in a soil composed of a less conductive upper soil layer overlying a more conductive subsoil and it also demonstrated that modifying the recently proposed sequential analysis procedure only using infiltration data could be advisable to determine the time when layering starts to influence the process.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"92 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135730386","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}
Paulina Deseano Diaz, Thai Nong, Nicolas Brüggemann, Maren Dubbert, Mathieu Javaux, Natalie Orlowski, Harry Vereecken, Youri Rothfuss
Abstract Using isotopic spike experiments, we investigated the existence and magnitude of soil‐mediated isotopic effects and of the interaction between isotopically distinct soil water pools, both associated in isotopic mismatches between water extracted from soil and soil water taken up by the roots. For this, we applied and compared four established techniques commonly used for the extraction of water (vapor) from soil, three of them relying on destructive soil sampling (cryogenic vacuum distillation, centrifugation, and direct water vapor equilibration), and one being a nondestructive in situ online technique. We observed an almost complete mixing of sequentially added, isotopically distinct water samples to a pure quartz sand (memory effect). The isotopic composition of water held at high soil tension in the pure quartz sand (pF = 2) as well as in a sandy soil (pF = 1.8 and 3) deviated considerably from that of the added water (tension effect). However, we could attribute this deviation not exclusively to a soil‐mediated effect but also to methodological shortcomings during our experiments. Finally, we found the following decreasing trend in precision as well as in accuracy of the used water extraction methods: in situ online > centrifugation > direct water vapor equilibration > cryogenic vacuum distillation. The investigation of isotopic fractionation of soil water due to physicochemical processes in soil can be facilitated if the experimental techniques used do not involve isotopic fractionation. In addition, methodological uncertainties and inaccuracies can be minimized by method standardization, increasing the potential of water stable isotopic monitoring in ecohydrological studies.
{"title":"Insights into tension‐mediated and antecedent water effects on soil water isotopic composition","authors":"Paulina Deseano Diaz, Thai Nong, Nicolas Brüggemann, Maren Dubbert, Mathieu Javaux, Natalie Orlowski, Harry Vereecken, Youri Rothfuss","doi":"10.1002/vzj2.20288","DOIUrl":"https://doi.org/10.1002/vzj2.20288","url":null,"abstract":"Abstract Using isotopic spike experiments, we investigated the existence and magnitude of soil‐mediated isotopic effects and of the interaction between isotopically distinct soil water pools, both associated in isotopic mismatches between water extracted from soil and soil water taken up by the roots. For this, we applied and compared four established techniques commonly used for the extraction of water (vapor) from soil, three of them relying on destructive soil sampling (cryogenic vacuum distillation, centrifugation, and direct water vapor equilibration), and one being a nondestructive in situ online technique. We observed an almost complete mixing of sequentially added, isotopically distinct water samples to a pure quartz sand (memory effect). The isotopic composition of water held at high soil tension in the pure quartz sand (pF = 2) as well as in a sandy soil (pF = 1.8 and 3) deviated considerably from that of the added water (tension effect). However, we could attribute this deviation not exclusively to a soil‐mediated effect but also to methodological shortcomings during our experiments. Finally, we found the following decreasing trend in precision as well as in accuracy of the used water extraction methods: in situ online > centrifugation > direct water vapor equilibration > cryogenic vacuum distillation. The investigation of isotopic fractionation of soil water due to physicochemical processes in soil can be facilitated if the experimental techniques used do not involve isotopic fractionation. In addition, methodological uncertainties and inaccuracies can be minimized by method standardization, increasing the potential of water stable isotopic monitoring in ecohydrological studies.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135732569","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}
Abstract Water behavior in bentonite clay pores is influenced by soil–water interaction mechanisms such as capillary and adsorptive forces. Quantitative measurement of these water statuses remains challenging, leading to the adoption of advanced techniques. This study uses low‐field nuclear magnetic resonance (NMR) technique to investigate water partitioning dynamics and changes in the water state in sodium‐rich Wyoming bentonite and calcium‐rich Denver bentonite under various humidity conditions. NMR T 2 relaxation and T 1 – T 2 mapping techniques, along with a multi‐Gaussian decomposition method, enable a quantitative analysis of capillary and adsorptive water in both bentonites. A conceptual water partitioning model is derived to explain water molecule trajectories of water molecules under unsaturated conditions. Our findings indicate distinct transitions in hydrated layers for Na + ‐smectite and Ca 2+ ‐smectite at different relative humidity (RH) ranges. Characteristic T 2 ranges are identified for capillary and adsorptive water in both clays and provide valuable insights into their water behavior. This study advances our understanding of soil properties at different RH environments and highlights the potential of low‐field NMR techniques in characterizing capillary and adsorptive water in bentonite clays.
{"title":"Water partitioning and migration in unsaturated bentonites by low‐field NMR characterization","authors":"Ling Peng, Fan Zhang, Yi Dong, Chi Zhang","doi":"10.1002/vzj2.20284","DOIUrl":"https://doi.org/10.1002/vzj2.20284","url":null,"abstract":"Abstract Water behavior in bentonite clay pores is influenced by soil–water interaction mechanisms such as capillary and adsorptive forces. Quantitative measurement of these water statuses remains challenging, leading to the adoption of advanced techniques. This study uses low‐field nuclear magnetic resonance (NMR) technique to investigate water partitioning dynamics and changes in the water state in sodium‐rich Wyoming bentonite and calcium‐rich Denver bentonite under various humidity conditions. NMR T 2 relaxation and T 1 – T 2 mapping techniques, along with a multi‐Gaussian decomposition method, enable a quantitative analysis of capillary and adsorptive water in both bentonites. A conceptual water partitioning model is derived to explain water molecule trajectories of water molecules under unsaturated conditions. Our findings indicate distinct transitions in hydrated layers for Na + ‐smectite and Ca 2+ ‐smectite at different relative humidity (RH) ranges. Characteristic T 2 ranges are identified for capillary and adsorptive water in both clays and provide valuable insights into their water behavior. This study advances our understanding of soil properties at different RH environments and highlights the potential of low‐field NMR techniques in characterizing capillary and adsorptive water in bentonite clays.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"136 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136115052","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}
Abstract Soil structure is an important factor interacting with soil erosion and sediment processes. However, few studies have focused on the relationship between soil macroporosity and soil erosion across different terrains. The aim of this study was to quantify and compare soil properties and macroporosity characteristics in collapsing gully areas and to explore their impact on the formation and development of collapsing gullies. Soil cores were excavated at different positions of a typical collapsing gully and then scanned to analyze soil macropores. Soil properties and saturated hydraulic conductivity were also investigated. The results showed that the contents of sand, silt, and clay, the mean weight diameter of aggregates, and the infiltrate rates varied at different positions. The valley had the greatest macroporosity (1.09% ± 0.33%), the number (5919 ± 703), volume (1468 ± 194 mm 3 ), and surface area (10.4 ± 2.6 m 2 ) of macropores, as well as the mean volume (16.8 ± 7.4 mm 3 ) of macropores >1 mm 3 , whereas these indices were lowest at the slope (0.15% ± 0.14%, 1189 ± 747, 266 ± 188 mm 3 , 1.7 ± 1.4 m 2 , and 10.6 ± 2.9 mm 3 , respectively). The macroporosity and the number of macropore decreased with increasing depth but were also influenced by the erosion and sediment processes. The processes of sediment and the roots of vegetation also influenced the orientation of the macropores. Macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity and further affected the processes of water erosion and mass erosion.
{"title":"Quantification of red soil macropores affected by slope erosion and sediment using computed tomography","authors":"Si‐Yi Zhang, Bin He, Beibei Hao, Depeng Lv","doi":"10.1002/vzj2.20276","DOIUrl":"https://doi.org/10.1002/vzj2.20276","url":null,"abstract":"Abstract Soil structure is an important factor interacting with soil erosion and sediment processes. However, few studies have focused on the relationship between soil macroporosity and soil erosion across different terrains. The aim of this study was to quantify and compare soil properties and macroporosity characteristics in collapsing gully areas and to explore their impact on the formation and development of collapsing gullies. Soil cores were excavated at different positions of a typical collapsing gully and then scanned to analyze soil macropores. Soil properties and saturated hydraulic conductivity were also investigated. The results showed that the contents of sand, silt, and clay, the mean weight diameter of aggregates, and the infiltrate rates varied at different positions. The valley had the greatest macroporosity (1.09% ± 0.33%), the number (5919 ± 703), volume (1468 ± 194 mm 3 ), and surface area (10.4 ± 2.6 m 2 ) of macropores, as well as the mean volume (16.8 ± 7.4 mm 3 ) of macropores >1 mm 3 , whereas these indices were lowest at the slope (0.15% ± 0.14%, 1189 ± 747, 266 ± 188 mm 3 , 1.7 ± 1.4 m 2 , and 10.6 ± 2.9 mm 3 , respectively). The macroporosity and the number of macropore decreased with increasing depth but were also influenced by the erosion and sediment processes. The processes of sediment and the roots of vegetation also influenced the orientation of the macropores. Macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity and further affected the processes of water erosion and mass erosion.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"178 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136115053","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}
Abstract Soil moisture is a key factor that influences various aspects of ecosystem functioning. Measuring soil moisture without installing any objects in the soil is desirable because it allows for accurate characterizations of soil moisture while minimizing impacts on soil structure and ecology. In this study, we explored the potential of leaky Rayleigh waves as a proxy to contactlessly estimate soil moisture. We developed an ultrasonic system containing a transducer, receivers, and acoustic barrier. The specimens of sand, silt, and clay were utilized. Experiments were conducted over 4 months. We used a widely used soil‐embedded moisture sensor to compare and develop relationships between leaky Rayleigh waves and soil moisture. Our results showed that as soil moisture increased, the velocity and amplitude of leaky Rayleigh waves decreased because water molecules attracted to the soils led to their attenuation. However, their magnitudes were not considerable except for very dry soils. To overcome these limited relations to estimate soil moisture from leaky Rayleigh waves, we constructed authentic images based on the observed leaky Rayleigh waves and used them as inputs for a fully convolutional network. We found that the combination of the ultrasonic system and deep learning approach developed in this study were suitable for estimating soil moisture without soil disturbances (RMSE = 0.01 m 3 m −3 ). This study suggests that leaky Rayleigh waves have the potential to serve as a reliable proxy for determining soil moisture without the need for physical contact.
土壤水分是影响生态系统各方面功能的关键因素。无需在土壤中安装任何物体即可测量土壤湿度是可取的，因为它可以准确表征土壤湿度，同时最大限度地减少对土壤结构和生态的影响。在这项研究中，我们探索了泄漏瑞利波作为非接触估计土壤湿度的代理的潜力。我们开发了一种包含换能器、接收器和声障的超声波系统。利用了砂、粉和粘土的试样。实验进行了4个多月。我们使用一种广泛使用的土壤嵌入式湿度传感器来比较和发展泄漏瑞利波与土壤湿度之间的关系。结果表明，随着土壤湿度的增加，漏失瑞利波的速度和振幅减小，这是由于土壤吸收的水分子导致其衰减。然而，除了非常干燥的土壤外，它们的大小并不大。为了克服这些有限的关系，从泄漏瑞利波中估计土壤湿度，我们基于观测到的泄漏瑞利波构建了真实图像，并将其用作全卷积网络的输入。我们发现，超声波系统和本研究开发的深度学习方法相结合适用于在没有土壤扰动的情况下估计土壤水分(RMSE = 0.01 m 3 m−3)。这项研究表明，漏瑞利波有潜力作为确定土壤湿度的可靠代理，而不需要物理接触。
{"title":"Contactless estimation of soil moisture using leaky Rayleigh waves and a fully convolutional network","authors":"Seoungmin Lee, Dong Kook Woo, Hajin Choi","doi":"10.1002/vzj2.20285","DOIUrl":"https://doi.org/10.1002/vzj2.20285","url":null,"abstract":"Abstract Soil moisture is a key factor that influences various aspects of ecosystem functioning. Measuring soil moisture without installing any objects in the soil is desirable because it allows for accurate characterizations of soil moisture while minimizing impacts on soil structure and ecology. In this study, we explored the potential of leaky Rayleigh waves as a proxy to contactlessly estimate soil moisture. We developed an ultrasonic system containing a transducer, receivers, and acoustic barrier. The specimens of sand, silt, and clay were utilized. Experiments were conducted over 4 months. We used a widely used soil‐embedded moisture sensor to compare and develop relationships between leaky Rayleigh waves and soil moisture. Our results showed that as soil moisture increased, the velocity and amplitude of leaky Rayleigh waves decreased because water molecules attracted to the soils led to their attenuation. However, their magnitudes were not considerable except for very dry soils. To overcome these limited relations to estimate soil moisture from leaky Rayleigh waves, we constructed authentic images based on the observed leaky Rayleigh waves and used them as inputs for a fully convolutional network. We found that the combination of the ultrasonic system and deep learning approach developed in this study were suitable for estimating soil moisture without soil disturbances (RMSE = 0.01 m 3 m −3 ). This study suggests that leaky Rayleigh waves have the potential to serve as a reliable proxy for determining soil moisture without the need for physical contact.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136013526","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}
Henrique D. R. Carvalho, Adam M. Howard, Aziz Amoozegar, Carl R. Crozier, Amy M. Johnson, Joshua L. Heitman
Abstract Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in “marginal” lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m −2 , 24 kg m −3 , and 1006 kg m −3 , respectively, giving a porosity of 0.98 m 3 m −3 . A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m −2 was 1.6 mm s −1 . During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a “critical” residue load (∼1.0 kg m −2 ) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining “critical” loads for different residue types is a knowledge gap that merits further research.
芒草是一种多产的多年生草本植物，适合作为生物能源作物在“边缘”土地(如水土流失土壤)低持水能力。然而，对芒草残茬对土壤水汽输送和水分收支的影响知之甚少。通过室内试验，测定了芒草残渣的蒸汽导率及其对土壤水分蒸发的影响。残基的长度为0.5 ~ 9.0 cm，宽度为0.1 ~ 0.5 cm，厚度为0.1 ~ 0.5 cm。平均残留面积、体积和骨架密度分别为0.88 kg m - 2、24 kg m - 3和1006 kg m - 3，孔隙率为0.98 m - 3。幂函数描述了电导随剩余负载的增加而减小。当残余负载为0.88 kg m−2时，相应的电导为1.6 mm s−1。在60天干燥试验的头几天，累积蒸发量随残留物负荷的增加呈对数衰减。相反，研究最后几天的累积蒸发量在处理之间几乎没有差异。测量表明，当土壤处于第1阶段蒸发状态时，存在一个“临界”残留负荷(~ 1.0 kg m - 2)，超过这个负荷，蒸发不再明显减少。结果表明，在边缘土地上保持适量的生物质秸秆覆盖土壤可以实现水土保持。确定不同残留物类型的“临界”负荷是一个值得进一步研究的知识缺口。
{"title":"Water vapor transport through bioenergy grass residues and its effects on soil water evaporation","authors":"Henrique D. R. Carvalho, Adam M. Howard, Aziz Amoozegar, Carl R. Crozier, Amy M. Johnson, Joshua L. Heitman","doi":"10.1002/vzj2.20282","DOIUrl":"https://doi.org/10.1002/vzj2.20282","url":null,"abstract":"Abstract Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in “marginal” lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m −2 , 24 kg m −3 , and 1006 kg m −3 , respectively, giving a porosity of 0.98 m 3 m −3 . A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m −2 was 1.6 mm s −1 . During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a “critical” residue load (∼1.0 kg m −2 ) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining “critical” loads for different residue types is a knowledge gap that merits further research.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136014128","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}
Johanna R. Blöcher, Efstathios Diamantopoulos, Wolfgang Durner, Sascha C. Iden
Abstract Evaporation from bare soil is an important hydrological process and part of the water and energy balance of terrestrial systems. Modeling bare‐soil evaporation is challenging, mainly due to nonlinear couplings among liquid water, water vapor, and heat fluxes. Model concepts of varying complexity have been proposed for predicting evaporative water and energy fluxes. Our aim was to test a standard model of coupled water, vapor, and heat flow in the soil using data from laboratory evaporation experiments under different boundary conditions. We conducted evaporation experiments with a sand and a silt loam soil and with three different atmospheric boundary conditions: (i) wind, (ii) wind and short‐wave radiation, and (iii) wind and intermittent short‐wave radiation. The packed soil columns were closed at the bottom (no water flux) and instrumented with temperature sensors, tensiometers, and relative humidity probes. We simulated the evaporation experiments with a coupled water, vapor, and heat flow model, which solves the surface energy balance and predicts the evaporation rate. The evaporation dynamics were predicted very well, in particular the onset of stage‐two evaporation and the evaporation rates during the stage. A continuous slow decrease of the measured evaporation rate during stage‐one could not be described with a constant aerodynamic resistance. Adding established soil resistance parametrizations to the model significantly degraded model performance. The use of a boundary‐layer resistance, which takes into account the effect of point sources of moisture, improved the prediction of evaporation rates for the sandy soil, but not for the silt loam.
{"title":"Validating coupled flow theory for bare‐soil evaporation under different boundary conditions","authors":"Johanna R. Blöcher, Efstathios Diamantopoulos, Wolfgang Durner, Sascha C. Iden","doi":"10.1002/vzj2.20277","DOIUrl":"https://doi.org/10.1002/vzj2.20277","url":null,"abstract":"Abstract Evaporation from bare soil is an important hydrological process and part of the water and energy balance of terrestrial systems. Modeling bare‐soil evaporation is challenging, mainly due to nonlinear couplings among liquid water, water vapor, and heat fluxes. Model concepts of varying complexity have been proposed for predicting evaporative water and energy fluxes. Our aim was to test a standard model of coupled water, vapor, and heat flow in the soil using data from laboratory evaporation experiments under different boundary conditions. We conducted evaporation experiments with a sand and a silt loam soil and with three different atmospheric boundary conditions: (i) wind, (ii) wind and short‐wave radiation, and (iii) wind and intermittent short‐wave radiation. The packed soil columns were closed at the bottom (no water flux) and instrumented with temperature sensors, tensiometers, and relative humidity probes. We simulated the evaporation experiments with a coupled water, vapor, and heat flow model, which solves the surface energy balance and predicts the evaporation rate. The evaporation dynamics were predicted very well, in particular the onset of stage‐two evaporation and the evaporation rates during the stage. A continuous slow decrease of the measured evaporation rate during stage‐one could not be described with a constant aerodynamic resistance. Adding established soil resistance parametrizations to the model significantly degraded model performance. The use of a boundary‐layer resistance, which takes into account the effect of point sources of moisture, improved the prediction of evaporation rates for the sandy soil, but not for the silt loam.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135591206","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}
Edward Smit, George van Zijl, Eddie Riddell, Johan van Tol
Abstract Detailed soil information is increasingly sought after for watershed‐scale hydrological modeling to better understand the soil–water interactions at a landscape level. In South Africa, 8% of the surface area is responsible for 50% of the mean annual runoff. Thus, understanding the soil–water dynamics in these catchments remains imperative to future water resource management. In this study, the value of hydropedological information is tested by comparing a detailed hydropedological map based on infield soil information to the best readily available soil information at five different catchment sizes (48, 56, 174, 674, and 2421 km 2 ) using the soil and water assessment tool (SWAT)+ model in the Sabie catchment, South Africa. The aim was to determine the value of hydropedological information at different scales as well as illustrate the value of hydropedology as soft data to improve hydrological process representation. Improved hydropedological information significantly improved long‐term streamflow simulations at all catchment sizes, except for the largest catchment (2421 km 2 ). It is assumed that the resulting improved streamflow simulations are a direct result of the improved hydrological process representation achieved by the hydropedological information. Here, we argue that hydropedological information should form an important soft data tool to better understand and simulate different hydrological processes.
{"title":"Examining the value of hydropedological information on hydrological modeling at different scales in the Sabie catchment, South Africa","authors":"Edward Smit, George van Zijl, Eddie Riddell, Johan van Tol","doi":"10.1002/vzj2.20280","DOIUrl":"https://doi.org/10.1002/vzj2.20280","url":null,"abstract":"Abstract Detailed soil information is increasingly sought after for watershed‐scale hydrological modeling to better understand the soil–water interactions at a landscape level. In South Africa, 8% of the surface area is responsible for 50% of the mean annual runoff. Thus, understanding the soil–water dynamics in these catchments remains imperative to future water resource management. In this study, the value of hydropedological information is tested by comparing a detailed hydropedological map based on infield soil information to the best readily available soil information at five different catchment sizes (48, 56, 174, 674, and 2421 km 2 ) using the soil and water assessment tool (SWAT)+ model in the Sabie catchment, South Africa. The aim was to determine the value of hydropedological information at different scales as well as illustrate the value of hydropedology as soft data to improve hydrological process representation. Improved hydropedological information significantly improved long‐term streamflow simulations at all catchment sizes, except for the largest catchment (2421 km 2 ). It is assumed that the resulting improved streamflow simulations are a direct result of the improved hydrological process representation achieved by the hydropedological information. Here, we argue that hydropedological information should form an important soft data tool to better understand and simulate different hydrological processes.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134960965","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}
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}
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