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Static chambers are commonly used to provide in situ quantification of nitrous oxide (N2O) fluxes. Despite their benefits, when left in the field, the physicochemical conditions inside the chamber's base may differ from the ambient, especially in drip-irrigated systems. This research aimed to study the effects of static chamber bases on water and N distribution and the subsequent impact on N2O fluxes. N2O emissions were measured in a drip-irrigated avocado orchard for 2 years, using bases with a dripper at their center (In) and bases installed adjacent to the dripper (adjacent). During the irrigation and fertigation season, the measured N2OIn fluxes were greater than the N2OAdjacent fluxes (0.015 ± 0.003 vs. 0.006 ± 0.001 g m−2 d−1). By contrast, during the winter, when the orchard is not irrigated or fertilized, insignificant differences were observed between the measured N2OAdjecent and N2OIn fluxes. Three-dimensional simulations of water flow, N transport, and N transformations showed two opposing phenomena: (a) increased water contents, N concentrations, and downward flushing when the dripper is placed inside the base, and (b) hampering of the lateral distribution of water and solutes into the most bio-active part of the soil inside the base when the base is placed adjacent to the dripper. It also showed that both “In” and “adjacent” practices underestimate the “true” cumulative flux from a dripper with no base by ∼ 25 % and ∼ 50 %, respectively. A nomogram in a non-dimensional form corresponding to all soil textures, emitter spacings, and discharge rates was developed to determine the optimal diameter of an equivalent cylindrical base to be used along a single dripline. Further studies under variable conditions (soil types, wetting patterns, nutrient availabilities), rather than a single study, are needed to test the constructiveness of the suggested methodologies.

Background Several observational studies have reported a decreased response to immune checkpoint inhibitors (ICI) following antibiotic use. ICI activity has been hypothesized to be impaired by antibiotic-induced gut dysbiosis. Methods Patients with advanced melanoma receiving an anti-PD-1 antibody as a first-line therapy between 2015 and 2017 in France were selected using the French Health Insurance database. We compared overall survival and time-to-treatment discontinuation according to antibiotic exposure in the 3 months prior to the initiation of anti-PD-1 antibody. To disentangle a causal effect of antibiotics from a confounding bias, we balanced characteristics of patients exposed and nonexposed to antibiotics using an overlap weighting method based on a propensity score. We also evaluated a control cohort of patients with advanced melanoma receiving first-line targeted therapy, as there is no rationale for decreased efficacy of targeted therapy following antibiotic treatment. Results The anti-PD-1 antibody cohort comprised 2605 individuals. Antibiotic exposure in the 3 months prior to anti-PD-1 antibody initiation was not associated with shorter overall survival (weighted hazard ratio = 1.01, 95% confidence interval = 0.88 to 1.17) or time-to-treatment discontinuation (weighted hazard ratio = 1.00, 95% confidence interval = 0.89 to 1.11). Consistent results were observed when the time frame of antibiotics was narrowed to 1 month prior to anti-PD-1 initiation or when exposure was restricted to antibiotics leading to more profound gut dysbiosis. Similar results were observed in the targeted therapy cohort. Conclusions In a large cohort of advanced melanoma patients, we showed that antibiotic use preceding anti-PD-1 antibody was not associated with worse outcome. Physicians should not delay immunotherapy for patients who have recently received antibiotics.

Introduction En raison de l’oncogenese induite par les rayons ultraviolets, la charge mutationnelle tumorale est classiquement elevee dans les melanomes cutanes. Elevee, elle est un biomarqueur predictif de reponse aux anti-PD-1, mais une telle richesse mutationnelle peut au contraire faciliter l’emergence precoce de clones resistants sous therapies ciblees. Nous avons emis l’hypothese que la survie post immunotherapie vs therapies ciblees en 1e intention dans le melanome avance peut varier selon du profil de photo exposition du site de survenue du melanome primitif. Materiel et methodes Dans le cadre de Melbase, biobanque multicentrique francaise dediee au suivi prospectif des melanomes non resecables de stade III/IV, tous les patients atteints d’un melanome cutane primitif connu, ayant recu un traitement systemique de 1e intention par immunotherapie ou therapie ciblee entre 2013 et 2019 ont ete inclus. Les criteres de jugement etaient la survie sans progression (SSP) et la survie globale (SG). Resultats Neuf cent soixante treize patients ont recu une monotherapie anti-PD-1 (n = 466), anti-CTLA-4 (n = 143), l’association des deux (n = 118), dabrafenib + trametinib (n = 187) ou vemurafenib + cobimetinib (n = 59). Les caracteristiques des patients au debut du traitement etaient : sexe masculin (62 %), âge median 62 ans, BRAFwt (58 %), stade AJCC IV (84 %), metastases cerebrales (18 %), ECOG 0-1 (84 %) et LDH normaux (52 %). Le suivi median etait de 15,5 mois. Le melanome primitif etait localise en peau chroniquement photo-exposee (G1 : tete cou, n = 175), en peau exposee par intermittence (G2 : tronc, bras, jambes, n = 615), ou en zone non photo-exposee (G3 : paumes, plantes, n = 65). La mediane de SSP etait significativement meilleure pour le groupe G1 sous anti-PD-1 (8,7 mois vs 3,3 et 3,4 mois pour G2 et G3, respectivement) (p = 0,011), tandis que la SSP semblait meilleure pour le groupe G3 sous therapies ciblees (19,2 mois vs 8,1 et 6 mois pour G2 et G1) (p = 0,31), non significativite possiblement liee au faible effectif G3 traite par therapie ciblee (n = 8). La SSP ne differait pas significativement entre groupes sous ipilimumab. De meme, la mediane de SG etait significativement plus elevee pour le groupe G1 post anti PD-1 en 1e ligne (45,6 mois vs 31,6 et 21,4 mois pour G2 et G3) (p = 0,04), par opposition a la mediane de SG observee post therapies ciblees (19,5 mois vs 16,3 et 21,1 mois pour G1, G2 et G3 respectivement). Discussion Notre etude suggere que les anti-PD-1 en premiere intention sont particulierement recommandes en contexte de melanome primitif survenu en zone chroniquement exposee au soleil. En revanche, les patients dont le melanome provient d’une zone non-photo-exposee pourraient beneficier davantage d’une therapie ciblee de 1e intention lorsque cela est possible (presence de mutation BRAF), mais ce resultat reste a confirmer par des recherches ulterieures.

Static chambers are frequently used to evaluate greenhouse gas (GHG) emissions from agro-systems. However, the effects of such chambers on water and nutrient distribution within and under the chamber’s base (i.e., anchor) in drip irrigation and its effects on GHG emissions is not well understood. This study aimed to shed some light on the topic by using field measurements and physically based, three-dimensional (3-D) simulations of flow transport and nitrogen transformations in variably saturated, spatially heterogeneous flow domain. GHG fluxes [methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)] were measured in the field for two years using a portable FTIR gas analyzer. The main findings of this study suggest that: (i) the chamber’s base modifies the water and nutrient distribution within it. Placement of the dripper inside the base leads to higher water contents, higher nitrate and ammonium concentrations, and higher N2O fluxes relative to an undisturbed area. In contrast, placement of the dripper outside the chamber base reduces all of these parameters, including the N2O fluxes, relative to an undisturbed area. (ii) The dripper’s location relative to the chamber’s base had minor to no effect on CO2 fluxes. The effect on the CH4 fluxes was not conclusive, yet suggested higher emissions when the dripper was located inside the base. (iii) A minimal disturbance is achieved when the dripper is located within a base, and the base’s radius equals the capillary length of the soil.

In 2016, the European Hematology Association (EHA) published the EHA Roadmap for European Hematology Research(1) aiming to highlight achievements in the diagnostics and treatment of blood disorders, and to better inform European policy makers and other stakeholders about the urgent clinical and scientific needs and priorities in the field of hematology. Each section was coordinated by one to two section editors who were leading international experts in the field. In the five years that have followed, advances in the field of hematology have been plentiful. As such, EHA is pleased to present an updated Research Roadmap, now including eleven sections, each of which will be published separately. The updated EHA Research Roadmap identifies the most urgent priorities in hematology research and clinical science, therefore supporting a more informed, focused, and ideally a more funded future for European hematology research. The eleven EHA Research Roadmap sections include Normal Hematopoiesis; Malignant Lymphoid Diseases; Malignant Myeloid Diseases; Anemias and Related Diseases; Platelet Disorders; Blood Coagulation and Hemostatic Disorders; Transfusion Medicine; Infections in Hematology; Hematopoietic Stem Cell Transplantation; CAR-T and Other Cell-based Immune Therapies; and Gene Therapy.

Objectives Abdominal aortic aneurysms with a wide proximal neck (>32 mm) are a contraindication for the use of conventional abdominal endovascular stent grafts because of their limited maximum proximal diameter (36 mm). In these cases, it is customary to resort to sophisticated techniques such as parallel or fenestrated grafts. In very selected cases, such as symptomatic wide neck aneurysm or patient with limited life expectancy, Funnel Technique may find an indication. Methods It consists in placing a bifurcated endograft in the abdominal aorta embricated with a thoracic endograft as a proximal cuff in an infrarenal position. Results In the literature review, we found 32 cases of this technique, whose characteristics are collected in a table. Conclusion The Funnel Technique, taking advantage of the larger diameters of the thoracic prostheses, may easily treat abdominal aortic aneurysm cases with a wide neck.

EnglishNon-pharmacological strategies for the treatment of carcinomas and melanomas. The most common skin cancers are basal cell and squamous cell carcinomas. They mainly affect elderly people. Consequently, their incidence is constantly growing. Melanomas are tumours presenting a high metastatic risk which concern people of all ages, but are rare in children. The non-pharmacological treatment of these cancers includes surgery, radiotherapy, as well as physical and topical treatments francaisLes cancers cutanes les plus frequents sont les carcinomes basocellulaires et epidermoides. Ils touchent essentiellement les personnes âgees. De ce fait, leur incidence est en constante augmentation. Le melanome est, quant a lui, une tumeur a haut potentiel metastatique qui concerne les personnes de tout âge, mais rare chez l’enfant. La prise en charge non medicamenteuse de ces cancers inclut la chirurgie, la radiotherapie, ainsi que les traitements physiques et topiques

The main goal of this study was to test the performance of irrigation water-based and soil-based approaches to control nitrate and chloride mass fluxes and concentrations below the root zone of agricultural fields irrigated with treated waste water (TWW). Using numerical simulations of flow and transport in relatively a fine-textured, unsaturated, spatially heterogeneous, flow domain, scenarios examined include: (i) irrigating with TWW only (REF); (ii) irrigation water is substituted between TWW and desalinized water (ADW); (iii) soil includes a capillary barrier (CB) and irrigating with TWW only (CB+TWW); and (iv) combination of (ii) and a CB (CB+ADW). Considering groundwater quality protection, plausible goals are: (i) to minimize solute discharges leaving the root zone, and, (ii) to maximize the probability that solute concentrations leaving the root zone will not exceed a prescribed, critical value. Results of the analyses suggest that in the case of a seasonal crop (a corn field) subject to irrigations only, with respect to the first goal, the CB+TWW and CB+ADW scenarios provide similar, excellent results, better than the ADW scenario; with respect to the second goal, however, the CB+ADW scenario gave substantially better results than the CB+TWW scenario. In the case a multi-year, perennial crop (a citrus orchard), subject to a sequence of irrigation and rainfall periods, for both solutes, and, particularly, nitrate, with respect to the two goals, both the ADW and CB+ADW scenarios perform better than the CB+TWW scenario. As compared with the REF and CB+TWW scenarios, the ADW and CB+ADW scenarios substantially reduce nitrogen mass fluxes to the groundwater and to the atmosphere, and, essentially, did not reduce nitrogen mass fluxes to the trees. Similar results, even better, were demonstrated for a relatively coarse-textured, spatially heterogeneous soil.

e21545 Background: The tumor mutational burden (TMB) is usually high in Cutaneous melanomas owing to ultraviolet radiation-induced oncogenesis. While a high TMB is a predictive biomarker of response to PD-1 inhibitors, it may be associated with the rise of resistant clones to targeted therapy over time. We hypothesized that the response pattern to immunotherapy and targeted therapy in advanced melanoma may vary depending on the sun-exposure profile of the site of primary melanoma. Methods: Patients were screened from MelBase, a French multicenter biobank dedicated to the prospective follow-up of unresectable stage III/IV melanoma. Within Melbase, all patients with a known cutaneous primary melanoma who received a first-line systemic treatment by immunotherapy or combined targeted therapy between January 2013 and November 2019 were included. Outcomes were progression-free survival (PFS ) and overall survival (OS). Results: 973 patients received either anti PD-1 monotherapy (n=466), anti CTLA-4 monotherapy (n=143), a combination of both (n=118), dabrafenib plus trametinib (n=187) or vemurafenib plus cobimetinib (n=59). Patients’ characteristics at treatment initiation were: male gender (62%), median age of 62 years old, BRAF WT (58%), AJCC stage IV (84%), brain metastases (18%), ECOG 0-1 (84%) and normal LDH (52%). Median follow-up was 15.5 months. The primary melanoma was located on chronically sun-exposed skin in 175 patients (G1: head neck), on intermittently sun-exposed skin in 615 patients (G2: trunk, arms, legs), and on sun-protected areas in 65 patients (G3: palms, soles, nails). Median PFS was significantly higher in G1 under anti PD-1 treatment (8,7 months vs 3,3 and 3,4 months for G2 and G3, respectively) (p=0.011), (19,2 months vs 8,1 and 6 months for G2 and G1) (p=0. although it is worthwhile to note that the number of G3 patients treated with targeted therapy was relatively low (n=8). PFS did not significantly differ between all groups under ipilimumab. Similarly, median OS was significantly higher in G1 receiving first-line anti PD-1 treatment (45,6 months vs 31,6 and 21,4 months for G2 and G3) (p=0.04), while OS was higher in G3 under targeted therapy (21,1 months vs 16,3 and 19,5 months for G2 and G1) (p=0.97). Conclusions: Our study suggests that first-line immunotherapy with anti PD-1 is particularly recommended for melanomas originating from chronically sun-exposed areas. On the other hand, melanomas originating from sun-protected areas may benefit more from first-line targeted therapy when possible (presence of BRAF mutation), but this finding needs to be confirmed by further research.

Treated wastewater (TWW) is an important water resource, especially in semiarid and arid regions. However, there are concerns that irrigation with TWW could lead to degradation of soil physical and hydraulic properties. The objective of our study was to determine the effects of long-term (≥ 15 years) irrigation with secondary TWW on some basic and hydraulic soil properties of a clay soil. Undisturbed soil samples (cores) were taken to a depth of 4.5 m (in sections of 0.5 m) over a diagonal cross section of a five year old orchard irrigated with TWW. Samples were taken from five sites within the tree rows (i.e., representing soil directly affected by TWW; referred to as “within rows”) and four sites between the rows of trees (i.e., the control treatment representing soil that was not directly subjected to the irrigation water; referred to as “between rows”). Soil analyses included an array of basic properties, determination of a continuous particle size distribution and measurement of the saturated hydraulic conductivity (HC). The latter two were used for the computation of soil characteristic curve, Θ(ψ), and the unsaturated HC curve, K(ψ). Similar bulk density, moisture content, cation exchange capacity, pH and exchangeable sodium percentage (ESP) levels were observed for the TWW irrigated samples and the control ones. However, irrigation with TWW caused a significant reduction in the saturated HC, Ks. The computed Θ(ψ) curve at a given soil depth, averaged over the different sites, was similar for the TWW-irrigated samples and the control ones. On the contrary, the computed K(ψ) curve at a given soil depth, averaged over the different sites, for the TWW-irrigated samples were lower than those for the control samples at matric potential ≳− 100 cm (= pF ≲ 2); similar K(ψ) values were noted at pF > 2 for the two treatments. The observed differences in the hydraulic properties between the TWW-irrigated samples and the control ones in this specific matric potential range, albeit the similarity in their ESP, suggest that long term irrigation with TWW affected structural porosity via narrowing macro- and mesopores (> 70 and 30–70 μm, respectively). It is further postulated that this adverse impact of irrigation with TWW on structural porosity might be associated with previously reported effects of TWW on the composition of the dissolved organic matter in the soil solution.

Summary A citrus orchard planted on a structured, clay soil associated with a high water table, irrigated by drip irrigation system using treated waste water (TWW) and local well water (LWW) was considered here. The scope of the present study was to analyze transport of mixed-ion, interacting salts in a combined vadose zone–groundwater flow system focusing on the following issues: (i) long-term effects of irrigation with TWW on the response of the flow system, identifying the main factors ( e.g. , soil salinity, soil sodicity) that control these effects, and (ii) salinity control aiming at improving both crop productivity and groundwater quality. To pursue this two-fold goal, 3-D numerical simulations of field-scale flow and transport were performed for an extended period of time, considering realistic features of the soil, water table, crop, weather and irrigation, and the coupling between the flow and the transport through the dependence of the soil hydraulic functions, K ( ψ ) and θ ( ψ ), on soil solution concentration C, and sodium adsorption ratio, SAR. Results of the analyses suggest that in the case studied, the long-term effect of irrigation with TWW on the response of the flow system is attributed to the enhanced salinity of the TWW, and not to the increase in soil sodicity. The latter findings are attributed to: (i) the negative effect of soil salinity on water uptake, and the tradeoff between water uptake and drainage flux, and, concurrently, solute discharge below the root zone; and, (ii) the tradeoff between the effects of C and SAR on K ( ψ ) and θ ( ψ ). Furthermore, it was demonstrated that a data-driven protocol for soil salinity control, based on alternating irrigation water quality between TWW and desalinized water, guided by the soil solution salinity at the centroid of the soil volume active in water uptake, may lead to a substantial increase in crop yield, and to a substantial decrease in the salinity load in the groundwater.

Detailed numerical analyses of flow and transport were used to investigate the effect of spatially connected features on transport in three-dimensional (3-D), spatially heterogeneous, combined vadose zone-groundwater flow systems. Formations with spatially connected fine-textured and coarse-textured features (F-formation and C-formation, respectively), representing the10th and the 90th percentiles of the distributions of the formation's hydraulic parameters, respectively, were considered here. Results of the analyses suggest that in steady state flow, when the unsaturated zone of the combined flow domains is relatively wet, as compared with a Multivariate-Gaussian (MG) formation, spatially connected features may reduce the solute first arrival time, particularly in the C-formation, and may enhance the spreading of the solute breakthrough, particularly in the F-formation. The effect of the spatially connected features on the hydrological response, however, decreases as the unsaturated zone becomes drier. The latter result stems from the decrease in the fraction of the water-filled, pore-space occupied by the connected structures, with decreasing water content. The latter finding also explains the result that the response of more realistic, combined flow systems, whose unsaturated zone is associated with relatively low, intermittent water contents, is essentially independent of the spatially connected features of the formations, regardless of their soil texture.

The challenge of meeting the projected doubling of global demand for food by 2050 is monumental. It is further exacerbated by the limited prospects for land expansion and rapidly dwindling water resources. A promising strategy for increasing crop yields per unit land requires the expansion of irrigated agriculture and the harnessing of water sources previously considered “marginal” (saline, treated effluent, and desalinated water). Such an expansion, however, must carefully consider potential long-term risks on soil hydroecological functioning. The study provides critical analyses of use of marginal water and management approaches to map out potential risks. Long-term application of treated effluent (TE) for irrigation has shown adverse impacts on soil transport properties, and introduces certain health risks due to the persistent exposure of soil biota to anthropogenic compounds (e.g., promoting antibiotic resistance). The availability of desalinated water (DS) for irrigation expands management options and improves yields while reducing irrigation amounts and salt loading into the soil. Quantitative models are used to delineate trends associated with long-term use of TE and DS considering agricultural, hydrological, and environmental aspects. The primary challenges to the sustainability of agroecosystems lies with the hazards of saline and sodic conditions, and the unintended consequences on soil hydroecological functioning. Multidisciplinary approaches that combine new scientific knowhow with legislative, economic, and societal tools are required to ensure safe and sustainable use of water resources of different qualities. The new scientific knowhow should provide quantitative models for integrating key biophysical processes with ecological interactions at appropriate spatial and temporal scales.

We study the standard deviation of water saturation SDS as function of the mean saturation (Formula presented.) by a stochastic model of unsaturated flow, which is based on the first-order solution of the three-dimensional Richards equation. The model assumes spatially variable soil properties, following a given geostatistical description, and it explicitly accounts for the different scales involved in the determination of the spatial properties of saturation: the extent L, i.e., the domain size, the spacing Δ among measurements, and the dimension (Formula presented.) associated to the sampling measurement. It is found that the interplay between those scales and the correlation scale I of the hydraulic properties rules the spatial variability of saturation. A “scale effect” manifests for small to intermediate L/I, for which SDS increase with the extent L. This nonergodic effect depends on the structural and hydraulic parameters as well as the scales of the problem, and it is consistent with a similar effect found in field experiments. In turn, the influence of the scale (Formula presented.) is to decrease the saturation variability and increase its spatial correlation. Although the solution focuses on the medium heterogeneity as the main driver for the spatial variability of saturation, neglecting other important components, it explicitly links the spatial variation of saturation to the hydraulic properties of the soil, their spatial variability, and the sampling schemes; it can provide a useful tool to assess the impact of scales on the saturation variability, also in view of the several applications that involve the saturation variability.

We examined the impact of two different approaches to managing irrigation water salinity: salt leaching from the field (“conventional” management) and water desalination before field application (“alternative” management). Freshwater commonly used for irrigation (FW) and desalinated water (DS) were applied to the high-water-demanding crop banana at four different rates. Both irrigation rate and water salinity significantly affected yield. DS application consistently produced higher yields than FW, independently of irrigation rate. The highest yield for FW-irrigation was achieved with the highest irrigation rate, whereas the same yield was obtained in the case of DS-irrigation with practically half the amount of water. Yield decreased with FW-irrigation, even when the water salinity, ECi, was lower than the limit considered safe for soil and crops. Irrigating with FW provided a massive amount of salt which accumulated in the rhizosphere, inducing increased osmotic potential of the soil solution and impairing plant water uptake. Furthermore, applying the “conventional” management, a significant amount of salt is leached from the rhizosphere, accumulating in deeper soil layers, and eventually reaching groundwater reservoirs, thus contributing to the deterioration of both soil and water quality. Removal of salt excess from the water before it reaches the field by means of DS-irrigation may save significant amounts of irrigation water by reducing the salt leaching requirements while increasing yield and improving fruit quality, and decreasing salt load in the groundwater.

The yield of avocado trees planted on clayey soils decreases due to irrigation with treated-waste water (TWW). We hypothesized that the main cause for this yield reduction is the reduction in water uptake by the trees roots. The aim of this numerical study was to identify the main soil factors that control the reduction in water uptake by the trees roots, and to test various soil substrate-based and water-based management schemes design to counterweigh the water uptake reduction. The study relies on physically based, three-dimensional (3-D) simulations of flow and transport in variably saturated, spatially heterogeneous, flow domain, conducted for three successive years. The main findings of this study suggest that: (i) the long-term effect of irrigation with TWW on the response of the flow system is attribute to the salinity of the TWW, and not to its sodium adsorption ratio, SAR; (ii) with respect to improving water uptake by the trees' roots, the water-based scheme that alternates irrigation water quality between TWW and desalinized water, DSW, (ADW) performed better than the water-based scheme that uses fresh water only (FW). The soil substrate-based schemes, TUFp, that used trenches with highly coarse-textured soil material and pulse irrigations, and, particularly, SAop, that used trenches with finer soil texture, performed substantially better than the soil substrate-based scheme that used trenches with highly coarse-textured soil material only (TUF); (iii) with respect to minimizing solute leaching below the root zone, the water-based schemes, FW, and, particularly, ADW, performed substantially better than the soil substrate-based schemes.

Field-scale transport of conservative and reactive solutes through a deep vadose zone was analyzed by means of two different model processes for the local description of the transport. The first is the advection-dispersion equation (ADE) model, and the second is the mobile-immobile (MIM) model. The analyses were performed by means of three-dimensional (3-D), numerical simulations of flow and transport considering realistic features of the flow system, pertinent to a turf field irrigated with treated sewage effluents (TSE). Simulated water content and concentration profiles were compared with available measurements of their counterparts. Results of the analyses suggest that the behavior of both solutes in the deep vadose zone of the Glil Yam site is better quantified by the MIM model than by the ADE model. Reconstruction of the shape of the measured solute concentration profiles using the MIM model required relatively small mass transfer coefficient, γ, and relatively large volume fraction of the immobile water θim. This implies that for an initially nonzero solute concentration profile, as compared with the MIM model, the ADE model may significantly overestimate the rate at which solutes are loaded in the groundwater. On the contrary, for an initially zero solute concentration profile, as compared with the MIM model, the ADE model may significantly underestimate solute velocities and early arrival times to the water table. These findings stem from the combination of relatively small γ and relatively large θim taken into account in the MIM model. In the first case, this combination forces a considerable portion of the solute mass to reside in the immobile region of the water-filled pore space, while the opposite is true in the second case.

Pollution of groundwater by nitrate originating from irrigated fields was considered for this study. We hypothesized that under cropped conditions, low-salinity irrigation water (e.g., desalinated water) could reduce nitrate leaching below the root zone, due to two possible mechanisms: (i) decreased vertical water fluxes and (ii) increased nitrogen uptake by plant roots due to chloride&ndash, nitrate competition. The main goal of this study was to investigate this hypothesis. Considering a citrus grove, the investigation relied on three-dimensional (3-D) simulations of flow and transport in a variably saturated and spatially heterogeneous flow domain performed for three successive years. Results of the analyses suggest that the main mechanism responsible for the reduction in the nitrate leached below the root zone under irrigation with low-salinity water is the effect of the latter on the spatial distribution of the rate of water uptake by the roots. The latter, in turn, significantly reduces water content, hydraulic conductivity, and vertical velocity, and, consequently, solute mass fluxes along the soil profile. On the other hand, chloride&ndash, nitrate interaction has only a relatively small effect on the nitrate mass fluxes at relatively deep soil depths, far below the root zone, particularly when the irrigation water salinity decreases.

Nitrate contamination of groundwater under land used for intensive-agriculture is probably the most worrisome agro-hydrological sustainability problem worldwide. Vadose-zone samples from 0 to 9 m depth under citrus orchards overlying an unconfined aquifer were analyzed for variables controlling water flow and the fate and transport of nitrogen fertilizers. Steady-state estimates of water and NO3-N fluxes to groundwater were found to vary spatially in the ranges of 90-330 mm yr(-1) and 50-220 kg ha(-1) yr(-1), respectively. Calibration of transient models to two selected vadose-zone profiles required limiting the concentration of NO3-N in the solution that is taken up by the roots to 30 mg L(-1). Results of an independent lysimeter experiment showed a similar nitrogen-uptake regime. Simulations of past conditions revealed a significant correlation between NO3-N flux to groundwater and the previous year's precipitation. Simulations of different nitrogen-application rates showed that using half of the nitrogen fertilizer added to the irrigation water by farmers would reduce average NO3-N flux to groundwater by 70%, decrease root nitrogen uptake by 20% and reduce the average pore water NO3-N concentration in the deep vadose zone to below the Israeli drinking water standard; hence this rate of nitrogen application was found to be agro-hydrologically sustainable. Beyond the investigation of nitrate fluxes to groundwater under citrus orchards and the interesting case-study aspects, this work demonstrates a methodology that enables skillful decisions concerning joint sustainability of both the water resource and agricultural production in a common environmental setting.

[1] Detailed numerical simulations were used to analyze water flow and transport of nitrate, chloride, and a tracer solute in a 3-D, spatially heterogeneous, variably saturated soil, originating from a citrus orchard irrigated with treated sewage water (TSW) considering realistic features of the soil-water-plant-atmosphere system. Results of this study suggest that under long-term irrigation with TSW, because of nitrate uptake by the tree roots and nitrogen transformations, the vadose zone may provide more capacity for the attenuation of the nitrate load in the groundwater than for the chloride load in the groundwater. Results of the 3-D simulations were used to assess their counterparts based on a simplified, deterministic, 1-D vertical simulation and on limited soil monitoring. Results of the analyses suggest that the information that may be gained from a single sampling point (located close to the area active in water uptake by the tree roots) or from the results of the 1-D simulation is insufficient for a quantitative description of the response of the complicated, 3-D flow system. Both might considerably underestimate the movement and spreading of a pulse of a tracer solute and also the groundwater contamination hazard posed by nitrate and particularly by chloride moving through the vadose zone. This stems mainly from the rain that drove water through the flow system away from the rooted area and could not be represented by the 1-D model or by the single sampling point. It was shown, however, that an additional sampling point, located outside the area active in water uptake, may substantially improve the quantitative description of the response of the complicated, 3-D flow system.

Solute transport in hillslope is often ruled by the water dynamics at the vadose zone and the groundwater. Solute is mobilized by rainfall, which feds the subsurface components of flow leading to water discharge and pollutograph at the outlet. It is often convenient to analyze solute transport through the travel time analysis. The latter is deeply influenced by the partitioning of the water ages. That is, rainfall typically mobilized pre-event (or “old”) water in the catchment, and the discharged water (and solute) is characterized by an age much larger than the one pertaining to the event water. We analyze solute transport in hillslope through a series of detailed numerical experiments. These are carried out through a three-dimensional saturated/unsaturated model, with realistic assumptions regarding the time- dependent rainfall and evapotranspiration forcing the flow system and the spatial distribution of the hydraulic properties. The scope is to analyze the travel time of rainfall in hillslopes as function of some selected characteristics and the seasonality of rainfall. We show that most of the river discharge is due to old water, i.e. rainfall coming from previous periods, sometimes very distant from the event. Also, each season displays a different travel time distribution for rainfall, as function of a few significant characteristics, like e.g. transpiration and the pre-event groundwater storage. The Equivalent Steady State approximation (ESS) for the analysis of solute transport is also tested.

Considering flow and transport in three-dimensional, variably saturated, composite bimodal heterogeneous formations, the main purpose of this study was to extend the previous analyses [37] , restricted to the one-region case in which the entire water-filled pore space is mobile, to the two-region case in which part of the water-filled pore space of each of the sub-soils of the composite formation is stagnant, and to investigate the effect of the interaction between the mobile and the immobile regions on solute transport in these formations. Following Russo [37] , formations with fine- and coarse-textured embedded soils (FTES- and CTES-formations, respectively), were considered in the analyses. Main results of the present study suggest that mass exchange between the two regions masks features of the transport that exist in bimodal, one-region flow domains, related to characteristics of the unsaturated hydraulic conductivity in variably saturated bimodal, heterogeneous formations. In particular, the crossover behavior (i.e., that under relatively wet conditions, solute spread is larger in the FTES-formations than in the CTES-formations, while the opposite occurs under relatively dry conditions) characterizing one-region, bimodal flow domains disappears in two-region, bimodal flow domains. The latter attributes to the transfer of mass from the mobile region to the immobile region and the extension of the capture zone for the solute particles associated with the fine-textured embedded soil to lower water saturations. Consequently, for both steady state- and transient-flows, as water saturation decreases, the response of the composite formations is essentially independent of the texture of the embedded soil.

First-order analysis was used to analyze the probability density function (PDF) of the logarithm of conductivity, log K , in variably saturated, bimodal, heterogeneous formations, and to investigate the implications of the results with respect to solute transport. The bimodal formations were viewed as mixtures of two populations (background soil and embedded soil) of differing spatial structures. Two distinct cases were considered: in the first case, the texture of the embedded soil is finer than that of the background soil, while the second case is the reverse situation. Results of this study suggest that, because for a given volume fraction of the embedded soil, both the mean and the variance of log K depend on the mean pressure head, H , in a manner that depends on the texture of the embedded soil relative to that of the background soil, so does the log K PDF. Furthermore, because of the inherent concave behavior of the log K variance–pressure head relationships in these formations, the shape of the bimodal log K PDF may change with increasing H , such that at a certain critical mean pressure head it may degenerate into an “equivalent,” unimodal PDF. One of the main findings of this study suggests that even when the two subdomains of the formation are characterized by mild heterogeneity, a relatively small volume fraction of coarse-textured embedded soil may lead to a highly skewed log K PDF, which, in turn, may exhibit an exceedingly large tail associated with the small K values, particularly when the contrast between mean conductivities of the two subdomains of the formation at saturation is relatively large and when the formation is relatively dry.

One of the alternative solutions to the problems associated with the agricultural use of stony desert soils is to apply imported soil material into trenches that are aligned along the crop rows. The purpose of the present study was twofold: first, to analyze the effect of two imported soil materials available in the Arava Valley of Israel on the movement and spread of water and solute originating from multiple trickle line laterals, taking into account the trench geometry, the discharge of the trickle line laterals, the pattern of the plant root distribution, and the spatial heterogeneity of the hydraulic properties of the local soil; and, second, to extend the analyses to hypothetical imported soil materials characterized by different sets of hydraulic parameters (saturated conductivity, K s , and the van Genuchten soil parameters α and n , related to the soil9s pore size distribution). Results of the present study suggest that in the case of relatively low-conductive imported soil materials, a wide and shallow trench may leach the solute below a horizontal control plane more efficiently than a narrow and deep trench, while the opposite is true for high-conductive imported soil materials. Combinations of the threshold values of K s and α above which a narrow and deep trench is more efficient in solute leaching than a wide and shallow trench calculated here suggest that, for a given n , a relatively large threshold value of K s may compensate for a relatively small threshold value of α, particularly when n is relatively large.

Summary The role played by subsurface flow in the rainfall–runoff transformation is still poorly understood. In particular, two aspects are highly debated. The first one is the relatively fast response of the catchments to rainfall input which is often observed. The rapid response contradicts the general notion of slow movement of water in the subsurface. Another important issue is the control of pre-event water to streamflow. In the present work, we perform a series of 2D numerical simulations in order to gain understanding on the above problems. The platform is the experimental site described in Montgomery and Dietrich [Montgomery, D.R., Dietrich, W.E., 2002. Runoff generation in a steep, soil-mantled landscape. Water Resour. Res. 38(9), 1168, doi:10.1029/2001WR000822]. The aim is not to replicate exactly the experimental conditions but rather to use the model as a numerical laboratory for investigating streamflow generation processes. The simulations show that a Darcian formulation of subsurface flow in a combined soil–bedrock system can generally reproduce fast catchment streamflow responses comparable to observations. The principal mechanisms for the streamflow generation are subsurface flow along the soil–bedrock interface combined with groundwater ridging in the vicinity of the hillslope base. Numerical analysis of solute transport indicates high proportions of pre-event water in the resulting hydrograph.

First-order analysis, based on a stochastic continuum presentation of flow and a general Lagrangian description of transport, was used to investigate the effects of several characteristics of a bimodal, spatially heterogeneous, variably saturated formation, on solute breakthrough curves, under steady-state, gravity-dominated unsaturated flow conditions. The bimodal formation was viewed as a mixture of two populations (background soil and embedded soil) of differing hydraulic properties and differing spatial structures. Results of the present analysis, restricted to relatively small inclusions' volume fraction, suggest that as in saturated flow, for a formation of given statistics and mean water saturation, both the spreading of the mean solute breakthrough curve and the uncertainty in its prediction may be appreciable, especially in bimodal formations in which: (i) the contrast between the mean properties of the two subdomains is relatively large, (ii) the inclusions' volume fraction is relatively large, and (iii) the characteristic length scales of the inclusions are relatively large as compared with those of the heterogeneity of the background soil. Results of this study, unique to unsaturated flow conditions, stem from the inherent concave nature of the log-conductivity varianceimean pressure head relationships in bimodal, variably saturated formations. Consequently, under unsaturated flow conditions, both the spreading of the mean solute discharge and the uncertainty in its prediction are concave functions of mean saturation. Starting with saturated formation, they initially decrease with decreasing mean saturation, reach their minima, and then increase as mean saturation further decreases, exceeding their counterparts in saturated flow conditions. Implications of the results with respect to the problem of groundwater contamination where risk assessment is required, are briefly discussed.

The purpose of the present study was to analyze movement and spreading of water and a passive solute (chloride) on a hillslope under surface drip irrigation, taking into account the texture of the soil, the slope of the terrain, the spatial heterogeneity of the soil hydraulic properties, and water extraction by plant roots. Results of the present investigation suggest that under surface drip irrigation, the movement and spread of water and solutes are affected mostly by the soil texture and less by the terrain slope. Increasing terrain slope is shown to increase the deflection of the trajectories of the centroid of the solute mass from the vertical axis, particularly in fine-textured soils associated with low saturated conductivity and considerable capillary forces, in which the interaction between adjacent drip line laterals may be appreciable. Transient flows originating from periodic water application and water uptake by plant roots are shown to enhance the effect of the terrain slope on water flow and solute movement, particularly in fine-textured soils. Implications regarding the problem of sensor placement with respect to drip irrigation management are briefly discussed.

The present study focuses on field-scale flow and transport in three-dimensional, heterogeneous, variably saturated formations, for the case in which the flow is coupled to the transport through the dependence of the hydraulic conductivity and water retentivity on solute concentrations. Numerical simulations of flow and transport of both tracer and mixed Na-Ca solutes were employed to analyze long-term effects of the interactions between the soil solution and the soil matrix on water and solute movement, under transient, nonmonotonic flows. The simulated flows were derived from actual irrigation and weather records, along with water uptake by plant roots. Results of this study suggest that enhanced soil solution-soil matrix interactions, induced by soil alkalinity and dilution of the soil solution, may reduce both the mean and the spatial variability of the hydraulic conductivity, and, concurrently, of the velocity. Consequently, enhanced soil solution-soil matrix interactions may slow down the tracer solute movement, decrease the spreading of the tracer solute about its center of mass (particularly in the vertical direction), diminish the skewing of the tracer solute breakthrough, and decrease both the magnitude of the effective retardation factor and the rate at which it approaches its asymptotic value. In addition, our results suggest that under realistic conditions, the three-dimensionality of the flow domain, the periodicity of the rain or irrigation events, along with the substantial redistribution periods between successive events, and the spatial heterogeneity of the hydraulic properties of the variably saturated formation may compensate in part for the adverse effects of soil alkalinity on flow and transport on the field scale. This last finding has practical implications regarding the use of sewage water for irrigation.