Soil Lysimeters Research Articles

Effects of Hydrochar Incorporation on the Nitrogen Leaching Flux Pattern and Load in Rice Paddy Soil and Crop Production

Hydrochar (HC) incorporation affects soil nitrogen (N) transformation, which could further affect the N leaching loss. We conducted a soil lysimeter experiment to evaluate the responses in terms of N leaching and rice yield to HC applied at a low (0.5%) or high (1.5%) rate, while considering three N inputs, i.e., 240, 192, and 144 kg/ha (named N240, N192, and N144, respectively). The results showed that the rice grain yield was highest (124.3 g/pot) for N192, while being significantly reduced to the minimum yield achieved in the study (110.3 g/pot) for N144. Interestingly, for the N input 144 kg/ha, HC application increased the rice grain yield by 6.9–8.0%, which was equivalent to that of N240. NH4+-N leaching occurred mainly during the first 4 weeks of the rice season, and HC did not influence NH4+-N leaching for both the N inputs, 192 and 240 kg/ha. However, compared to N144, N144 + HC1.5% recorded a significantly higher NH4+-N leaching loss of 34.6%. This suggests that the application of a high amount of HC increases the NH4+-N leaching risk when the N input is low. HC application resulted in 10.2–45.3% more NO3−-N leaching loss when the three N inputs were applied, the effect of which was significant in regard to the applications involving a 20 and 40% N reduction, but this occurred only with the applied treatments involving 1.5% HC. Moreover, we found that organic N was the main form of leachate N (>80%). More specifically, N144 + HC recorded 7.8–8.3% lower organic N leaching than N192. Based on the effects of HC on the rice grain yield and N leaching, we recommend applications involving a 40% N reduction (N144) with a lower amount of HC (HC 0.5%) to ensure high crop production and to protect the water environment.

Estimation of water productivity with adjustment of rice cultivation period using paddy soil lysimeters

Estimation of water productivity with adjustment of rice cultivation period using paddy soil lysimeters

Hydrotreated vegetable oil migrates through soil and degrades faster than fossil diesel and hydrotreated vegetable oil-fossil diesel blend

HVO has been noted as a more sustainable fuel, not only leading to lower total CO2 emissions, but also resulting in lower emissions of toxic substances upon fuel burning. The environmental impact of HVO and HVO diesel blends when accidentally spilled into the soil and ground water has, however, received little attention. While HVO and diesel exhibit nearly identical viscosity and density, their behavior in soils differs due to varying water solubility and fuel additives. In laboratory- and pilot-scale soil columns and lysimeters, we compared the migration and biostimulation-enhanced degradation of HVO, HVO-diesel blend (HVO15), and fossil diesel over 120 days. Additionally, we investigated the impact of fuel additives on migration by comparing HVO without additives to HVO15 and diesel in wet and dry soil columns over 21 days. Notably, HVO migrated through soil more rapidly and in greater quantities than diesel. In wet soil, 69% of added HVO, 8.4% of HVO15, and 21% of diesel leached through as light non-aqueous phase liquid (LNAPL). Dry soil showed smaller differences in fuel migration, but HVO did not mobilize when water was added, unlike HVO15 and diesel. Biostimulation reduced HVO leaching by 15% more than HVO15 and 48% more than diesel. Overall, HVO’s behavior in soil differs significantly from fossil diesel, with factors like lower water solubility, reduced mobilization from dry soil, and higher in situ degradability contributing to its reduced environmental risk compared to fossil fuel alternatives in accident scenarios.

Mechanisms underlying episodic nitrate and phosphorus leaching from poorly drained agricultural soils.

Poorly drained depressions within tile-drained croplands can have disproportionate environmental and agronomic impacts, but mechanisms controlling nutrient leaching remain poorly understood. We monitored nitrate and soluble reactive phosphorus (SRP) leaching using zero-tension soil lysimeters across a depression to upland gradient over 2 years in a corn-soybean (Zea mays L.-Glycine max [L.] Merr.) field in Iowa. We also measured stable isotopes (δ15N and δ18O) of nitrate to examine its sources and transformations. SRP concentrations peaked during winter and early spring after phosphorus (P) fertilization (mean=3mg P L-1), with highest values in the depression, and SRP was relatively stable thereafter (mean=0.3mg P L-1) irrespective of periods of high soil moisture that led to widespread iron (Fe) reduction across the field. During a near-average precipitation year, nitrate stable isotopes indicated direct leaching of fertilizer nitrate within days of application, followed by nitrification of fertilizer ammonium and several weeks of denitrification in depressional soils. Nevertheless, nitrate concentrations remained high (mean=28mg N L-1) in the depression despite strong isotopic evidence for denitrification (>48% N removal). During a wet year, nitrate concentrations were lower in the depression than upland and nitrate isotopes were highly variable, consistent with nearly complete nitrate removal by denitrification in the depression and significant denitrification in upland soils. We conclude that poorly drained depressional soils can potentially decrease nitrate leaching via denitrification under sustained wet conditions, but they inconsistently denitrify and are vulnerable to high nitrate and SRP losses when soils are not saturated, especially following fertilization.

A low-cost simple lysimeter soil retriever design for retrieving soil from small lysimeters

A lysimeter-soil retriever (LSR) is a device used to retrieve the soil with minimum disturbance from lysimeters. This device makes the process of sampling intact soil layers from lysimeters easier and faster, especially when a large number of lysimeters are being sampled. In this study, mini lysimeters (200 mm diameter and 25 kg weight) were used to test fertilizers. A low-cost LSR was designed to aid the accurate removal of the soil from these lysimeters. This paper describes the design and testing of the suitability of a linear actuator for this application. This study investigates the influence of soil moisture on the retrieval and structural stability of lysimeter and LSR. The results revealed that soil with a high moisture level was more suitable as it showed lower disturbance for the retrieved block, lower soil losses, minimal disturbance for roots and lower variation of soil block height and weight. The retrieval time was influenced by soil moisture level and were 48 and 52 s for low and high-moisture soils, respectively. The finite element model showed that the stress applied by the linear actuator on the lysimeter body and top-wood plate were 2.18 and 0.32 MPa, respectively. These stress values were within the safe limit of the corresponding materials. It was found that the selected linear actuator is suitable for soil retrieving from lysimeters packed with sandy-clay loam and sand. It showed consistent performance (stroke time and maximum force) after retrieval of 400 soil blocks. The suitability of this design for various soil types needs to be tested to determine its applicability in a broader range of scenarios.

Reduced weeding shows potential to regulate nutrient leaching in a cabbage (Brassica oleracea, var. capitata) lysimeter trial

Agricultural land is the main contributor to nitrogen and phosphorus pollution of groundwater sources. Adopting agroecological management practices can support the transition towards sustainable farming systems. We investigated if reduced weeding could support nutrient retention in a nutrient demanding vegetable crop (Brassica oleracea, var. capitata), without causing unacceptable yield losses. We conducted a three-year study (2019–2021) with two cropping seasons (autumn and spring) using 1 m3 above-ground lysimeters, each containing four cabbage plants. Different vegetation covers, each with four replicates, were considered: 1) crop only 2) weeds only 3) crop + weeds from crop transplanting 4) crop + weeds after 20 days from crop transplanting 5) bare soil with fertilizer 6) bare soil without fertilizer. Each system received the recommended dose of mineral fertilizer for cabbage (130 kg ha−1 N, 80 kg ha−1 P, 150 kg ha−1 K), except for two bare soil lysimeters which were not fertilized. Water samples were taken throughout the growing season, in particular after each fertilization event, and analysed for nitrate (NO3-N), phosphorus (P) and potassium (K) concentrations. Cabbage yield in both weedy treatments was significantly lower compared to the weed-free plots only in spring 2020 and fall 2021. Weed cover contributed to explain NO3-N and K leaching, while P leaching was affected by crop cover. The results suggest that it is possible to reduce weed management intensity in cabbage while also obtaining some benefits concerning nutrient losses.

Size-resolved distribution of trace elements in lysimeter soil solutions under contrasting long-term agricultural management to assess their bioavailability

The chemical species of trace elements (TEs) in agricultural soils is highly variable under diverse conditions, requiring tools with clear resolution and minimal disturbance for exploration. A novel surgical (316L) stainless steel (SS) lysimeter with a 5 μm pore size was developed to collect field soil solutions. The size-resolved distribution of TEs were characterized into total (nitric acid digestion), particulate (0.45–5 μm), dissolved (<0.45 μm), colloidal (1 kDa to 0.45 μm), and mainly ionic (<1 kDa) fractions in the lysimeter soil solutions. Total concentrations of TEs (dry weight basis) in acid digested Gray Luvisolic soils were analyzed. Most TEs in lysimeter soil solutions were present in particulate phases, relevant to their geochemical affinities and occurrences in soil minerals. Among dissolved fractions, As, Ba, Co, Li, Mn, Tl, and V existed as mainly ionic species in the soil solutions. Copper, Pb, Al, Th, and U showed variable associations with dissolved organic matter (DOM) and/or inorganic colloids among agricultural treatments. Inorganic NPKS or NKS fertilizer applications with lower pH (5.25–5.74) enhanced mobility and potential bioavailability of Ba, Co, Li, Mn, and Pb present in mainly ionic species, compared with other locations (pH 5.82–6.37). Manure application exhibited a dual effect, potentially increasing bioavailability for As, Tl, and V due to probably enhanced cation exchange capacity (CEC), while also facilitating specific adsorption of Cu and U on DOM, potentially reducing their bioavailability depending on DOM molecular weight. Colloidal and ionic Al and Th concentrations were higher in forest soils than agricultural soils, with extremely low potential bioavailability of Th attributed to strong precipitation with inorganic colloids and adsorption on DOM. The lysimeter sampling and size fractionation method provided a clear insight into agricultural effects on TE distributions and enhancing understanding of agricultural soil health in terms of TE bioavailability in situ.

Исследование динамики влажности почвы при капельном поливе

Purpose: to study the dynamics of moisture in soils on the drainage layer during drip irrigation to save water resources and ensure uniform watering of crops using moisture contours. Materials and methods. The study is based on the theory of moisture transfer under the influence of drip irrigation on soil. Moisture contours were studied in laboratory conditions using a soil lysimeter, which was used to model the geological cross-section of the irrigated area, represented by alluvial meadow soils formed on pebbles. The pebble layer thickness was assumed to be up to 3 m. A regression analysis of moisture movement was carried out, and a mathematical model describing the nature of its movement on the drainage layer was obtained. The estimated volume of wet soil was defined on the basis of moisture contours as a result of calculating the volume of the formed lathe object using cartograms for each hour of irrigation. Results. Data on the moisture distribution in soil profile according to irrigation hours, presented on cartograms constructed using a personal computer, were obtained. The contours with the same humidity – isolines on which the humidity was displayed: 5; 10; 40 % are highlighted on the cartograms. It has been determined that water at an emitter discharge of 2.5 l/h reaches the drainage layer 4 hours after the beginning of irrigation. The graph for moisture distribution in soil volume by hour, reflecting the dynamics of water distribution supplied from an emitter with a constant discharge over 10 hours of irrigation has been constructed. Conclusion. The dynamics of moisture distribution during drip irrigation in soils located on a drainage bed was studied. Under experimental conditions, when crop irrigation lasts for more than 8 hours, an ineffective excess of irrigation rate and an increase in the design capacity of the drip irrigation system are observed.

Subsurface Seep Irrigation Effects on Omnivorous Nematode Vertical Distribution in Lysimeters

Subsurface seep irrigation is a common practice in Florida histosol soils to supply water to crops by utilizing high-water tables. This study evaluated the effect of subsurface and overhead irrigation methods on plant-parasitic and free-living nematode densities in 46-cm soil lysimeters in a greenhouse study. Lysimeters were planted with bahiagrass in 2019 and wheat in 2020 and irrigated with subsurface or overhead irrigation for 12 weeks. Nematodes were extracted and quantified at 5-cm depth increments. Nematode counts were subjected to analysis of variance to compare treatment effects. Among nematode functional groups, omnivores were the most affected by irrigation method, their abundance being lower in subsurface-irrigated lysimeters than in overhead-irrigated ones. The results of this study show that omnivore nematode density and depth distribution are impacted by irrigation method.

Preferential flow in the shallow vadose zone: Effect of rainfall intensity, soil moisture, connectivity, and agricultural management

AbstractPreferential flow is ubiquitous in soils, and it affects water infiltration, runoff, and contaminant transport. Undisturbed soil lysimeters (n = 10; 900 cm2) were collected from an agricultural field to quantify the effect of climate, soil moisture, connectivity, and agricultural practices on water transport through the shallow vadose zone. A series of 10 rainfall simulations was conducted on each lysimeter (n = 100 events) and data were analysed within a framework of five case studies where we assessed the impact of rainfall intensity (n = 30 events), soil moisture (n = 28), and tillage (n = 21). Three lysimeters that had near‐zero flow initially were modified to investigate dynamics of direct surface connectivity through an artificial macropore in which we assessed the impacts of soil moisture (n = 12) and subsequent disruption via tillage (n = 9). Stable water isotopes were used to separate leachate into event (Qe) and pre‐event water (Qpe). Results showed that event water transport in leachate was not affected by rainfall intensity (Qe/Q = 49% ± 21% to 50% ± 24%); however, event water decreased from 65% ± 5% to 23% ± 28% with increasing soil moisture. Lysimeters with artificial macropores resulted in leachate that was nearly all event water (85% ± 12% to 92% ± 4%) irrespective of soil moisture. Tillage decreased event water transport for both lysimeters with and without an artificial macropore by ~30%. Findings show how varying initial and boundary conditions produce a continuum of preferential flow. Water and tracer flux data collected in the current study are therefore essential for predicting conditions with high relevance of preferential flow and contaminant transport when assessing or modelling long‐term hydrographs where these conditions are only met during a small proportion of the flow time.

A virtual tracer experiment to assess the temporal origin of root water uptake, evaporation, and drainage

AbstractThe temporal origin of drainage, evaporation, and root water uptake (RWU) are indicators of ecosystem functioning that shed light on how natural and anthropogenic disturbances affect plant resilience and aquifer vulnerability. A virtual tracer experiment was carried out in HYDRUS‐1D using data from a soil lysimeter planted with winter rye in Austria. The RWU (τR), evaporation (τE), and drainage (τD) transit times (τ) were determined by using the actual dispersivity optimized in a prior study. First, τR and τD were compared to RWU (τPT,R) and drainage (τPT,D) advective transit times estimated using the particle tracking algorithm. The τR values were in agreement with τPT,R while large discrepancies were detected when estimating drainage transit times using the two approaches. A sensitivity analysis revealed that dispersivity had a mild, poor, and strong influence on τR, τE, and τD. The longitudinal dispersivity describes how a tracer spreads along the flow paths. The longer the flow paths, the more dispersion affects the tracer transport. On average, water parcels originating from rainfall in the growing season took 18 and 201 days to reach the roots (with RWU being 21% of rainwater) and the soil profile bottom (with drainage being 36% of rainwater), respectively. In contrast, 10% of rainwater that fell in the dormant season became RWU after 264 days, while 79% became drainage after 294 days. The temporal origin of water can be explored in other plots by using the guidelines proposed in this study.

ON THE COMPARATIVE ANALYSIS OF THE COMPOSITION OF LYSIMETRIC WATER UNDER CONDITIONS OF DIFFERENT SOIL TREATMENT AND UNDER PHYTOCENOSES

A comparative analysis of the composition of lysimetric waters for 2021–2022 was carried out. for two groups of stationary soil lysimeters in the city. The first group of lysimeters is formed by the system: fallow — grass phytocenosis — overgrown fallow — spruce forest — mixed and broadleaved plantation, developing on the same type of mantle loam. The second group of lysimeters represents soils with different types of tillage: conventional plowing, extradeep planting according to Bushinsky, plowing according to Mosolov, deep plowing according to Kachinsky.For both groups, the same type of migration of components is shown, in which the most migrating elements are carbon, mono- and divalent cations, and chloride ion, with minimal migration of iron, manganese, and aluminum.In the group of lysimeters under various types of vegetation, as the tree canopy develops and, accordingly, the intensity of the biological cycle increases in migrating waters, the concentration of such important biophilic elements as magnesium, calcium, potassium, and carbon increases significantly, and among anions, chloride and sulfate ions. This determines, within the framework of the cluster analysis, two different subgroups in terms of the composition of natural waters: the first one is formed by the fallow-grass phytocenosis — overgrown fallow system, and the second one combines tree plantations.In the group of lysimeters with different tillage, a cluster characterizes the composition of water in lysimeters with reclamation plowing according to Mosolov and deep plowing according to Kachinsky. At the same time, individual aggregates form lysimeters with conventional plowing and ultradeep planting according to Bushinsky. This is explained by the fact that in this group of lysimeters, the initially created soil profile design is transformed, which is characterized by the placement of eluvial and illuvial soil horizons in various combinations and at different depths depending on the type of plowing.

Environmental fate of chlorpyrifos in Rhodic Ferralsol grown with corn during summer and winter seasons under high-intensity rainfall

The interactions between pesticides' physicochemical properties and edaphoclimatic factors influence their distribution into the environment. Understanding how those factors interact in a changing environment is crucial for mitigating environmental and agronomic problems. Thus, a percolation lysimeter with undisturbed soil and suction lysimeters were used to conduct a field study to evaluate the distribution of chlorpyrifos sprayed in a corn crop cultivated in a Rhodic Ferralsol in simulated extreme rainfall conditions. The mobility of chlorpyrifos was evaluated under simulated precipitation (150 mm h−1), 24 h and 48 h after applying the chlorpyrifos in different phenological stages of corn during the summer and winter crops in two agricultural years. In addition, GC-ECD determined the residual concentration of chlorpyrifos in the runoff and leached samples. Finally, a laboratory adsorption study was conducted with Rhodic Ferralsol to find the chlorpyrifos adsorption capacity in different temperatures, with and without soil organic matter. Our results show that soil organic matter is essential in chlorpyrifos adsorption, responsible for approximately 5% pesticide retention, which could be 25% higher during winter. High-intensity rainfalls positively affect runoff and leaching; nevertheless, these are responsible for only 0.2% of all chlorpyrifos amounts, as the soil is the major reservoir of chlorpyrifos by retention into clays and organic matter. Furthermore, the corn growth stages directly affect chlorpyrifos transportation, with higher amounts observed in runoff and leaching during the first and last corn growth stages. Therefore, in the conditions such as high-intensity rainfall, exposed soil, shallow soil profile, and temperatures below 20 °C, attention should be paid to chlorpyrifos spray with special regard to the weather forecast, avoiding its spray near rainfall events. Further studies should be conducted in other soil classes and rainfall conditions to validate our observations.

Labile carbon inputs support the recovery of bacterial communities, but not fungal communities, from a simulated bovine urine event

Inputs of carbon to soil may be used to stimulate microbial growth and immobilize excess nitrogen from sources such as livestock urine. However, the growth responses of microbial taxa to carbon inputs under conditions of excess soil nitrogen remain poorly understood. Using DNA metabarcoding and a field-based soil lysimeter experiment, we characterised the temporal responses (up to 112 days) of bacterial and fungal communities to a simulated bovine urine event plus inputs of labile carbon (sucrose) at two concentrations. Fungal communities were impacted more strongly than bacterial communities by carbon inputs following the simulated urine event, with more variable responses among taxa. Chytridiomycota and Glomeromycota richness were most negatively affected, and Tremellomycetes richness most positively affected, by carbon inputs. A minority of fungal ASVs had greatly increased proportional abundances in response to carbon, while fungal trophic composition became highly dominated by saprotrophs by the experiment end. Bacterial taxa showed consistent trends of declining (to about 14 days) and recovering (to 112 days) richness in response to urine and carbon inputs, but carbon-related evenness and proportional abundance trends varied between taxa. Proportional abundances of Actinobacteria, Bacteroidetes, Betaproteobacteria, and Gammaproteobacteria increased in response to carbon, whereas proportional abundances of Acidobacteria, candidate division WPS-1, Planctomycetes, Deltaproteobacteria, and Verrucomicrobia decreased. These results show that labile carbon inputs to limit nitrate leaching support the recovery of bacterial communities to bovine urine events but may have long-term impacts on fungal community composition and function, with potential consequences for soil food webs, carbon sequestration, and agricultural productivity.

Contaminant uptake in wastewater irrigated tomatoes

As population growth and climate change add to the problem of water scarcity in many regions, the argument for using treated wastewater for irrigation is becoming increasingly compelling, which makes understanding the risks associated with the uptake of harmful chemicals by crops crucial. In this study, the uptake of 14 chemicals of emerging concern (CECs) and 27 potentially toxic elements (PTEs) was studied in tomatoes grown in soil-less (hydroponically) and soil (lysimeters) media irrigated with potable and treated wastewater using LC-MS/MS and ICP-MS. Bisphenol S, 2,4 bisphenol F, and naproxen were detected in fruits irrigated with spiked potable water and wastewater under both conditions, with BPS having the highest concentration (0.034–0.134 µg kg−1 f. w.). The levels of all three compounds were statistically more significant in tomatoes grown hydroponically (<LOQ - 0.137 µg kg−1 f. w.) than in soil (<LOQ - 0.083 µg kg−1 f. w.). Their elemental composition shows differences between tomatoes grown hydroponically or in soil and tomatoes irrigated with wastewater and potable water. Contaminants at determined levels showed low dietary chronic exposure. When the health-based guidance values for the studied CECs are determined, results from this study will be helpful for risk assessors.

Estimation of Daily Evaporation from Shallow Groundwater Using Empirical Models with a Temperature Coefficient

Abstract Shallow groundwater evaporation (Eg) is a major component of the hydrological cycle, especially in semiarid and arid locations. Empirical methods are commonly used to estimate Eg. However, most of these methods can only weakly represent Eg variations along the soil depth and do not consider the energy driver. In this paper, a temperature coefficient was proposed and incorporated into two preferred empirical models to characterize the impacts of soil temperature and air temperature lags on Eg. The method was evaluated using in situ daily data obtained from nonweighing bare soil lysimeters. The results indicated that the models that considered the temperature gradient variable (T) conformed to the changes in the actual Eg values with depth more appropriately than the original models, accompanied by 4.3%–8.8% accuracy improvements overall. Shallow groundwater evaporation Eg was found to be influenced by the water table depth (H), T, and pan evaporation (E0) in descending order, and strong interactions were found between H and T. Moreover, the impact of precipitation on Eg was investigated; measurements from dry days without precipitation revealed the actual Eg process, the relative errors in the cumulative Eg values derived at different depths demonstrated a positive relationship with infiltration recharge, and the errors related to precipitation induced 6.7%–8.3% Eg underestimations. These results contribute to a better understanding of evaporative losses from shallow groundwater and the typical Eg situation that occurs simultaneously with recharge, and they provide promising perspectives for corresponding integrated hydrologic modeling research.

Wheat Crop Yield and Changes in Soil Biological and Heavy Metals Status in a Sandy Soil Amended with Biochar and Irrigated with Drainage Water

The current research aims to study the impacts of adding corncob biochar to a sandy soil irrigated with drainage water on wheat productivity, heavy metals fate, and some soil properties that reflect healthy soil conditions. This research consists of two separate experiments under field (lysimeters) and pot incubation conditions conducted on sandy soil irrigated with drainage water and treated with corncob biochar at the rate of 0.0, 1, 2, and 3% as mixing or mulching. Results specified that drainage water electrical conductivity value (5.89 dS m−1) lies under the degree of restriction on use of “Severe”, indicating that nonstop irrigation with such drainage water may cause a severe salinity problem in soil in the long run. A comparison of heavy metal concentrations of biochar-treated soils with the control showed that total heavy metals had accumulated significantly in the topsoil layer. Most of the available heavy metal concentrations in all soil leachate fractions were below the method detection limits. Mean concentrations of Ni, Cd, and Pb in wheat crops were far below the concentrations considered phytotoxic to wheat plants. More than 90% of the Ni, Cd, and Pb contained in the drainage water of the Al-Moheet drain were significantly present (p ≤ 0.05) and adsorbed by biochar in the top 20 cm of soil lysimeters, indicating the high biochar adsorptive capacity of heavy metals. Total counts of bacteria and fungi gradually and significantly increased over the soil incubation time despite irrigation with contaminated drainage water. Soil resistance index (SRI) values for microbial biomass were positive throughout the experiment and increased significantly as the application rate of corncob biochar increased. These results indicated the high feasibility of using corncob biochar at a rate of 3% to temporarily improve the health of sandy soil despite irrigation with drainage water.

Improved Lumped-Parameter and Numerical Modeling of Unsaturated Water Flow and Stable Water Isotopes.

Characterizing unsaturated water flow in the subsurface is a requirement for understanding effects of droughts on agricultural production or impacts of climate change on groundwater recharge. By employing an improved lumped-parameter model (LPM) approach that mimics variable flow we have interpreted stable water isotope data (δ18 O and δ2 H), taken over 3 years at a lysimeter site located in Germany. Lysimeter soil cores were characterized by sandy gravel (Ly1) and clayey sandy silt (Ly2), and both lysimeters were vegetated with maize. Results were compared with numerical simulation of unsaturated flow and stable water isotope transport using HYDRUS-1D. In addition, both approaches were extended by the consideration of preferential flow paths. Application of the extended LPM, and thus varying flow and transport parameters, substantially improved the description of stable water isotope observations in lysimeter seepage water. In general, findings obtained from the extended LPM were in good agreement to numerical modeling results. However, observations were more difficult to describe mathematically for Ly2, where the periodicity of seasonal stable water isotope fluctuation in seepage water was not fully met by numerical modeling. Furthermore, an extra isotopic upshift improved simulations for Ly2, probably controlled by stable water isotope exchange processes between mobile soil water and quasi-immobile water within stagnant zones. Finally, although LPM requires less input data compared with numerical models, both approaches achieve comparable decision-support integrity. The extended LPM approach can thus be a powerful tool for soil and groundwater management approaches.

A Bayesian perspective on the information content of soil water measurements for the hydrological characterization of the vadose zone

Transient measurements from soil water monitoring installments are frequently coupled with Richards-based solvers to inversely estimate soil hydraulic parameters (SHPs) and numerically describe vadose zone water fluxes, such as groundwater recharge. To reduce model predictive uncertainty, the experimental setup should be designed to maximize the information content of observations. However, in practice, this is generally done by relying on the a priori expertise of the scientist/user, without exploiting the advantages of model-based experimental design. Thus, the main aim of this study is to demonstrate how model-based experimental design can be used to maximize the information content of observations in multiple synthetic scenarios encompassing different soil textural compositions and climatic conditions. The hydrological model HYDRUS is coupled with a Nested Sampling estimator to calculate the parameters’ posterior distributions and the Kullback-Leibler divergences. Results indicate that the combination of seepage flow, soil water content, and soil matric potential measurements generally leads to highly informative designs especially for fine textured soils, while results from coarse soils are generally affected by higher uncertainty. Additionally, the propagation of parameter uncertainties in a contrasting (dry) climate scenario strongly increased prediction uncertainties for sandy soil, not only in terms of the cumulative amount and magnitude of the peak, but also in the temporal variability of the seepage flow. A complementary real-world application with a sandy soil lysimeter identified a combination of seepage data and matric potential as the most informative design and confirmed findings of the synthetic scenarios, in which matric potential proved to be more informative than soil water content measurements.

Evaluating the Distribution of Perfluoroalkyl Substances in Rice Paddy Lysimeter with an Andosol.

The properties of potential emerging persistent contaminants, perfluoroalkyl substances (PFAS), in an andosol rice paddy lysimeter were analyzed to determine their mobility and leaching behavior regarding carbon chain length and functional groups. For this purpose, simulated contaminated water (ΣPFAS = 1,185,719 ng/L) was used in the lysimeter. The results showed that PFAS distribution in the paddy soil lysimeter was influenced by the migration of these substances into irrigation water and their adsorption into the soil. PFHxS (C6) and PFOS (C8), which are the main components of the simulated contaminated water, were mostly captured in the soil layers of the low-humic andosol layer (0–35 cm). PFAS distribution may depend on soil properties, such as total carbon (TC) content. Compared with perfluoroalkane sulfonic acids (PFSAs), the distribution of perfluoroalkyl carboxylic acids (PFCAs) in soil showed significant variation. The remaining PFCAs were distributed across all layers of the lysimeter, except for the longer-chain PFCAs. Moreover, the PFSA distribution was directly correlated with the carbon chain number, whereby longer- and shorter-chain PFSAs accumulated in the top and bottom soil layers, respectively. This study provides detailed information on the distribution, leaching, uptake, and accumulation of individual PFAS in andosol paddy fields in Japan.