Vadoze Zone Research Articles

DRASTIC Index Mapping for Identifying Areas of High Aquifer Pollution Risk in a Mechanic Village: A Case Study of Reclaimed Nekede Mechanic Village Owerri, Imo State Nigeria

The DRASTIC index mapping was used to investigate areas of high aquifer pollution risk in Reclaimed Nekede Mechanic Village Owerri, Nigeria. A total of six vertical electrical soundings were probed within the study area to obtain data on the depth to water table, net recharge, aquifer media, soil media, topography, impact of vadoze zone and hydraulic conductivity. These seven parameters are denoted by the acronym, DRASTIC, a widely used technique for assessing groundwater vulnerability to pollution based on the hydrogeological settings of the area. The deduced DRASTIC parameters were used to map the groundwater vulnerability of the study area. The mapping shows that the location Near Otamiri River is an area of low vulnerability to pollution and the locations Along Church Road and Erosion Site are areas of moderate vulnerability to pollution. The rest of the locations within the study area have high vulnerability. The study concluded that the groundwater reserve is at a high risk of contamination due to the disposition of the hydrogeological environment of the area.

Application of DRASTIC method to identify the groundwater vulnerability to pollution in the sub-district of West Limboto and Limboto, Gorontalo Regency, Indonesia

The increment in population and agricultural sectors in West Limboto and Limboto, Gorontalo, affects the increased production of pollutants. The community uses shallow groundwater as the main water source. Since shallow groundwater is vulnerable to pollution due to community activity, this study aims to identify its vulnerability in West Limboto and Limboto. It was identified using the DRASTIC Method that will be integrated with Geographic Information System (GIS) Technique. The used parameters are Depth to Water Table, Recharge, Aquifer Media, Soil Media, Topography, Impact of Vadoze Zone, and Hydraulic Conductivity of the Aquifer. Depth to Water Table data is obtained from direct field measurement. Recharge amount data is obtained from the calculation of groundwater recharge. Aquifer Media, the Impact of Vadoze Zone, and Soil Media data are obtained from surface and subsurface geological data. Topography data is obtained from Digital Elevation Model Map. Hydraulic Conductivity is obtained from Pumping Test Data. The analysis result shows that the groundwater vulnerability of the study area was classified into 2 classes, the high index was in the southern part, and the low index was in the middle to the northern part of the study area.

Importance of Infiltration Rates for Fate and Transport of Benzene in High-Tiered Risk-Based Assessment Considering Korean Site-Specific Factors at Contaminated Sites

Widely used conservative approaches for risk-based assessments of the subsurface transport processes have been calculated using simple analytical equations or general default values. Higher-tier risk assessment of contaminated sites requires the numerical models or additional site-specific values for input parameters. Previous studies have focused on the development of sophisticated models fit into risk-based frameworks. Our study mainly aims to explore the applicability of site-specific parameters and to modify the risk-based fate and transport model according to the types of the site-specific parameters. To apply the modified fate and transport equation and the site-specific default infiltration range, this study assessed the source depletion, leachate concentrations, and exposure concentration of benzene, which is a representative organic contaminant. The numerical models consist of two continuous processes, the fate and transport of contaminants from (1) the soil to the groundwater table in the vadose zone and subsequently (2) from the groundwater table to exposure wells in the saturated zone. Spatially varied Korean domestic recharge data were successfully incorporated into site-specific infiltration parameters in the models. The numerical simulation results were expressed as transient time series of concentrations over time. Results presented the narrow range of predicted concentrations at the groundwater table when site-specific infiltration was applied, and the dilution–attenuation factors for the unsaturated zone (DAFunsat) were derived based on the prediction. When a contaminant travels to the longest path length of 10 m with a source depth of 1 m in the vadoze zone, the simulated DAFunsat ranged from 3 to 4. The highest DAFunsat simulation results are close to 1 when contaminants travel to a source depth of 5 m and the shortest path length of 1 m. In the saturated aquifer below the contaminated sites, the variation in exposure concentration with time at monitoring wells is detected differently depending on the depth of the saturated zone.

Optimization-based upscaling for gravity segregation with 3D capillary heterogeneity effects

Multiphase flow driven by gravity and capillary forces occurs in various applications pertaining to aquifers, the vadoze zone and hydrocarbon reservoirs. In particular, these processes have been under investigation for modeling CO2 migration in geosequestration applications. Solving such multiscale problems can be extremely computationally demanding and therefore upscaling is often employed. However, a recent study by Rabinovich and Cheng, 2020 showed that implementation of conventional upscaling methods fails to reproduce fine-grid simulations of gravity-capilary driven flow. This work presents a new upscaling method based on an effective property formula for permeability (k), power law averaging in the capillary limit for relative permeability, and an optimization approach for capillary pressure (Pc). The new method is tested on various example cases and coarse-grid simulations are shown to match fine-grid ones with sufficient accuracy. The challenge of upscaling the flows is found to be related to entry pressure trapping and the optimization upscaled Pc is shown to have a unique structure allowing to model the trapping. The method is global, requiring a fine-grid simulation for calibration of the optimized parameters. However, we show that the method reduces computational time dramatically if calibrated parameters are used in cases in which the fine-grid solution is unknown, such as for varying k realizations.

LNAPL Migration in Vadoze Zone and Its Prevention Using Natural Fiber

ABSTRACT Light non-aqueous phase liquids (LNAPLs) spilt over an area can be a persistent and long-term source of groundwater contamination. Once the groundwater gets contaminated, it is difficult to remediate. Migration of the spilt LNAPL should be contained within the unsaturated zone of the soil such that the LNAPL does not reach the groundwater source. Although the presence of LNAPLs in the unsaturated zone is also a long-term source, the provision of proper liners can contain the LNAPL within this region. The use of natural fiber as a liner in the unsaturated zone can be a sustainable solution to this problem if it can effectively contain the LNAPL. The objective of the present study was to investigate whether the use of natural fiber (coir geotextile) has supplemented the inherent attenuation characteristics of soils in the unsaturated zone thereby controlling the LNAPL migration. The study reveals that coir geotextiles were more effective in reducing the LNAPL migration in laterite soil than in sandy soil. Coir geotextiles are effective in controlling the migration of LNAPL if these are embedded in the soil with permeability less than 2.30 × 10−05 m/s.

Modern state of irrigated soils at the south of the Volga upland

The goal is to assess the impact of 50-year irrigation by sprinkling on soil processes occurring in the light-chestnut soils (Luvic Kastanozem (Loamic, Aric, Protosodic, Bathysalic)) of the southern slopes of the Volga upland at the Volga-Don interfluve (FSUE “Oroshaemoe”, the Volgograd region) with deep ground water. Water for irrigation is supplied from the Varvarovsky reservoir of the Volga-Don Canal system. It is characterized by a total dissolved salts of about 1 g/l, a bicarbonate-chloride-sulfate compositionwith an increased sodium content. Detailed morphological description of soil profiles, granulometric composition, content of soluble salts in soils and sediments of the vadoze zone up to the depth of 3.5 m, dynamics of salts in the layer of 0-50 cm for 2011-2019 are presented. Until the autumn of 2015, the studied soils were deep saline, being no saline in the layer of 0-100 cm. In recent years, a weak salinity degree of soda-chloride sodium chemistry has been observed in the 0-50 cm layer as a result of gradual accumulation of irrigation water salts during irrigation organized according to water consumption of agricultural crops. Irrigated soils have acquired a complex of signs of secondary salinity: (1) the presence of light accumulations of sandy and silt mineral grains in the arable horizon, resulting from the destructive effect of irrigation water drops during sprinkling; (2) toxic alkalinity associated with sodium (residual sodium carbonate), according to water extraction 1 : 5 (soil : water), in the horizons from the depth of 10-20 to 60100 cm; (3) abundant humus-clay cutans on the lateral side faces of prismatic structural units in the undisturbed part of the soil profile from 30 to 100 cm.

Assessment of the Protective Capacity of Vadoze Zone over Aquifer Systems Using Secondary Geoelectrical Parameters: A Case Study Of Kaltungo Area North East, Nigeria

An assessment of the protective capacity of the vadose zone overlying the aquifer systems in the Kaltungo area was carried out to determine its influence on groundwater quality. Applying the schlumberger array with a maximum electrode spread AB/2 = 100m through VES, thirty water well points were surveyed using Omega terrameter (PIOSO1) resistivity meter. The field data was first subjected to manual interpretation through curve marching and then digitized modeled curves using computer software. The interpreted data revealed that the area is characterized by eleven different curve types representing three to five geo electrical layers. In order to assess the protective capacity of the vadoze zone over the aquifer systems, the longitudinal conductance (S) and transverse resistance (T) (secondary geoelectric parameters) were computed from the primary data using the Dar Zarouk formula. The values of S obtained range from 0.0018 to 0.4056 ohms with a mean value of 0.0135 ohms while the values of T range from 0.55 ohms to 1195.68 ohms with a mean value of 39.84 ohms. The values of S and T obtained reveal that 90% of probed points has poor protective capacity, 10 % has moderate protective capacity and 83 % has high transmissivity, 17 % has intermediate transmissivity. The T and S values are skewed towards poorly protective capacity thus making groundwater in the area highly vulnerable to contamination from the surface. To achieve good groundwater quality in the area, proper completion of newly constructed wells should install protective casing through the entire vadose zone.

Numerical Experiments on Fate and Transport of Benzene with Biological Clogging in Vadoze Zone

A one-dimensional numerical model is developed to predict the benzene concentration in the unsaturated zone with special emphasis on the impact of biological clogging on benzene transport while the bacteria remain in mobile condition. The numerical results suggest that the water saturation during the biological clogging condition reaches its maximum value of approximately 51% after nearly 20 days, whereas the water saturation reaches the maximum value (approximately 54%) within 3 days in the absence of clogging condition while the bacteria remain mobile. A similar trend has been observed at greater depths also. Further, the results indicate that the hydraulic conductivity profile during the presence of biological clogging shows an increasing trend from its initial value, which is observed later in time when the depth increases, whereas the increase in hydraulic conductivity occurs very early for the entire depth during the absence of biological clogging. Similar observations are also experienced for the benzene concentration profile during the scenario of mobile bacteria. Conversely, immobile bacteria play a predominant role on accumulation of more bacteria in the shallow depths as compared with mobile bacteria and eventually increase the microbial saturation. Moreover, the peak value of hydraulic conductivity and benzene concentration are considerably reduced during the presence of biological clogging during the immobile bacterial condition. This situation yields the larger residence time in the shallow depths, which in turn enhances the biodegradation of benzene in the shallow depths; hence, the groundwater contamination by benzene in the deeper zone is prevented.

Sensitivity of the results of modeling of seasonal ground freezing to selection of parameterization of the snow cover thermal conductivity

The relationship between the results of calculations of the dynamics of the temperature regime of the in freezing and thawing soil profile with the heating effect of the snow cover is considered. To analyze this connection, two coupled models are used: the model of formation and degradation of snow cover in winter and the model of heat transfer and soil moisture transport in underlying vadoze zone profile. Parametrization of the influence of the snow cover, which at each calculated moment of time has the current average density and depth, on the dynamics of the temperatures of the soil profile is due to the use of its specific thermal resistance, which depends on its current depth and the thermal conductivity coefficient. The coefficient of thermal conductivity of the snow cover is related with its density using six different published empirical relationships. Modeling of heat transfer in freezing and thawing soil is carried out on the example of the field site for monitoring the thermal regime located on the territory of the Zvenigorod Biological Station of Moscow State University. It is shown that the well-known relationships give similar curves for the dynamics of the depth of seasonal freezing, including the degradation of the seasonal freezing layer in the spring period, with the same dynamics of the snow cover. However, the maximum penetration depth of the zero isotherm differs significantly for different snow conductivity-snow density relationships. The tested six relationships were divided into three groups. Minimal freezing is provided by the Sturm model and the effective medium model. The average and rather poorly differentiating freezing from each other is given by the Pavlov, Osokin et al. and Jordan relationships. The greatest value of the freezing depth is obtained with using Pavlov’s relationship with a temperature correction.

Hydrological Observatories Featured in VZJ Special Section

Hydrological Observatories Featured in VZJ Special Section

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

Abstract. In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these processes is crucial to assess effects of changed environmental conditions on the future development of these ecosystems. We show that the Richards equation can be used to accurately describe the moisture dynamics under evaporative conditions in variably saturated peat soil, encompassing the transition from the topmost living moss layer to the decomposed peat as part of the vadose zone. Soil hydraulic properties (SHP) were identified by inverse simulation of evaporation experiments on samples from the entire acrotelm. To obtain consistent descriptions of the observations, the traditional van Genuchten–Mualem model was extended to account for non-capillary water storage and flow. We found that the SHP of the uppermost moss layer reflect a pore-size distribution (PSD) that combines three distinct pore systems of the Sphagnum moss. For deeper samples, acrotelm pedogenesis changes the shape of the SHP due to the collapse of inter-plant pores and an infill with smaller particles. This leads to gradually more homogeneous and bi-modal PSDs with increasing depth, which in turn can serve as a proxy for increasing state of pedogenesis in peatlands. From this, we derive a nomenclature and size classification for the pore spaces of Sphagnum mosses and define inter-, intra-, and inner-plant pore spaces, with effective pore diameters of > 300, 300–30, and 30–10 µm, respectively.

Hydrological Responses and Flow Pathways in an Acrisol on a Forested Hillslope with a Monsoonal Subtropical Climate

The nature of subsurface flow depends largely on hydraulic conductivity of the vadoze zone, permeability of the underlying bedrock, existence of soil layers differing in hydraulic properties and macropore content, soil depth, and slope angle. Quantification of flow pathways on forested hillslopes is essential to understand hydrological dynamics and solute transport patterns. Acrisols, with their argic Bt horizons, are challenging in this respect. To further elucidate flow pathways of water and short-term variability of soil moisture patterns in Acrisols, a field study was conducted on a forested hillslope in a sub-catchment of the Tie Shan Ping (TSP) watershed, 25 km northeast of Chongqing City, China. This catchment is covered by a mixed secondary forest dominated by Masson pine (Pinus massoniana). Soil saturated hydraulic conductivity (Ksat) was significantly reduced at the interface between the AB and Bt horizons (2.6 × 10−5 vs. 1.2 × 10−6 m s−1), which led to that the flow volume generated in the Bt horizon was of little quantitative importance compared to that in the AB horizon. There was a marked decrease in porosity between the OA and AB horizons, with a further decrease deeper in the mineral subsoil. Especially, the content of soil pores > 300 μm was higher in the AB horizon (14.3%) than in the Bt horizon (6.5%). This explained the difference in soil Ksat values. This study showed that Bt horizon had limited water transport capability, forcing part of the infiltrated rainwater as interflow through the OA and AB horizons. Thus, the topsoil responded quickly to rainfall events, causing frequent cycles of saturation and aeration of soil pores.

Assessment of soil and Groundwater Contamination by Heavy Metals and Metalloids in Russian and Indian Megacities

A comparative assessment of heavy metal and metalloids pollution in soils and groundwater was carried out at the key sites in two megacities, i.e., Hyderabad (India) and Moscow (Russia), as a part of Indo-Russian collaborative research project. The geological structure, hydrogeological conditions and contamination of soils and groundwater were studied at the key sites and contaminants migration in the vadoze zone and groundwater was simulated. The results of statistical analysis prove that at the key site in Hyderabad the elevated concentrations of some chemical elements leading to soil pollution with heavy metals (i.e. Cd, Cu, Pb and Zn) are related to technogenic and industrial activities. The modeling of ground- and surface water contamination showed that the area of sewage influence on groundwater is limited and that there is no hazard of river water contamination in the long-term perspective1. The fill ground and ancient alluvium at the key site in Mоscow manifest the multi-element (Pb, Cu, Zn, Ni, Cd, Mn, Cr, As, oil products) contamination of soil, which is substantially variable both by depth and area. The modeling results permitted assessing the hazard of contaminated soils as the secondary long-acting source of groundwater contamination. The geological structure and hydrogeological differences between the key sites determined the use of different models for the investigation of heavy metals migration in the vadoze zone and in the aquifers.

Examining the influence of TBM-ground interaction on electrical resistivity imaging ahead of the TBM

Tunnel excavation by means of tunnel boring machines (TBMs) is susceptible to unknown changes ahead of the tunnel face. Geophysics offers a technique called electrical resistivity that can continuously, in real-time, spatially map the formation in front of the TBM. Electrical resistivity has been successfully established for many applications including vadoze zone hydrology, oil/gas location, mineral location and failure detection in geo-structures. Yet it has not been well-established for TBM excavations. This is in part due to the complexity of the TBM tunneling environment and the uncertain influence this environment may have on the success of TBM-integrated-electrical resistivity to predict changes ahead of the tunnel face. One significant uncertainty lies in the interface region that exists around the TBM created during the modification of the virgin formation by a mechanical mixing action of the rotating cutterhead and the injection of additives used to aid in the extraction of the muck and protect the cutting tools from frictional wear. In this study, we investigate the influence of this interface region on TBM-integrated-electrical resistivity for both hard rock and soft ground tunneling conditions through finite element modeling. Regarding the performance of TBM-integrated-electrical resistivity to detect changes ahead of the cutting face, the interface region holds significant influence for both earth pressure balance (EPB) and open mode tunneling conditions. Electrical resistivity for slurry based tunneling is not influenced by the interface region. Simulations suggest that TBM-integrated-electrical resistivity can be sensitive to a formation change that is located up to five diameters in front of the TBM.

Estimating S-index, unsaturated hydraulic conductivity and diffusivity through RETC in Indian Agricultural Research Institute farm

The hydraulic properties of vadoze zone like hydraulic conductivity, diffusivity and soil water retention characteristics are required to study soil water, nutrient and pollutant dynamics and their management. Surface layer of ten master profiles of Indian Agricultural Research Institute (IARI) farm, New Delhi were studied for different physicochemical and hydraulic properties. All ten master profiles were grouped under the order Inceptisol, subgroup Typic Haplustept and hyperthermic soil temperature regime. The soil water retention data were measured for all the sample layers and fitted to van Genuchten model using RETC software. The R2 value of fitted curve varied between 0.98 to 0.99 with residual sum of squares from 0.001 to 0.003. The θr value varied between 0.0332 to 0.0760 cm3 cm−3 and the saturated water content between 0.4665 to 0.3613 cm3 cm−3. In the present study, α ranged between 0.0018 to 0.0164 cm−1. The n value varied between 1.381 to 2.437. Combined for all profiles the prediction equation developed for K(θ) is K(θ) = 1.17×106×θ11.93 and D(θ) is D(θ) = 2.07×107× θ7.71 with R2 value of 0.77 both for K(θ) and D(θ). The Sindex varied between 0.068 to 0.128. The S-index was significantly positively correlated with θr (r = 0.73*), θs (r = 0.64*), n (r = 0.97**) and significantly negatively correlated with α (r = -0.80**). The S-index value for all the 10 master profiles were more than 0.050 indicating very good physical quality for all the 10 master profiles of IARI experimental farm.

PH-dependent reactive transport of uranium(VI) in unsaturated sand

Uranium contamination of subsurface environments was once thought to be an isolated occurrence, mostly at production sites. But recent evidence has shown that the presence of uranium in phosphate fertilizers has caused massive amounts of this element to be released worldwide. Concerns are related to uranium movement to groundwater supplies and its significant toxicological risks to human populations. Information is direly needed on how geochemical processes control uranium transport in the vadose zone. Laboratory experiments were performed to investigate the effects of the pH of the soil solution on the reactive transport of uranium(VI) in the vadose zone. The uranium solution was prepared by dilution of a 10−3 M stock solution of uranium perchlorate, (UO2(ClO4)2), with DI water. Two U(VI) solutions were prepared at concentrations of 2 × 10−6 M at pH 6 and 11 and were percolated under steady-state conditions through columns filled with sand. The convective-dispersion equation (CDE) was used to analyze the tracer and uranium breakthrough curves resulting from the column experiments. The program CXTFIT was used to estimate the transport parameters of equilibrium and nonequilibrium (i.e., two-site and mobile-immobile) models applied to the experimental data. Comparison of U(VI) breakthrough behavior at pH 6 with that of a nonreactive tracer indicated that U(VI) transport was significantly retarded, and about 52 % of the added U(VI) adsorbed to the quartz sand, likely in the cationic forms UO2OH+ and UO 2 2 + . The adsorption was reversible upon the addition of deionized water. At pH 11, the U(VI) breakthrough curve increased gradually and reached a plateau value C/C 0 oscillating between 72 and 82 %. Upon reaction, Si was released from the dissolution of quartz sand, which allowed the possible transport of U(VI) following precipitation of a U(VI) containing solid, such as uranyl-silicate minerals, or sorption of U(VI) onto silica colloids. Two-site and mobile-immobile (MIM) models suggested an influence of either rate-limited mass transfer processes or immobile/mobile water partitioning in U(VI) reactive transport. The reactive transport of U(VI) governed by adsorption-desorption processes, precipitation, and complexation reactions in which kinetic behaviors are controlled by pH, solution chemistry, and heterogeneous flow regime impacts the mobility of U(VI). The column transport experiments indicated that under geochemical conditions and vadoze zone processes (preferential flow) that favor the mobility of U(VI), dissolved- and colloidal-phase associations of U(VI) may be transported rapidly and in high concentrations from the soil surface to the groundwater.

Application of digital techniques to identify aquifer artificial recharge sites in GIS environment

Because the groundwater is considered as the major source of 99% of all retrievable fresh water, optimization of its usage would be very crucial. Groundwater artificial recharge (GAR) using surface water is the recommended solution because that increases the aquifer storage. Detection of aquifer storage site is the first step in designing GAR projects. The main objective of this research is the identification of suitable GAR sites scattered in the Shahrekord plain, Chaharmahal-va-Bakhtiari province of Iran, using Boolean and Fuzzy logic. Data affecting GAR including ground surface slope, soil infiltration rate, vadoze zone thickness, electrical conductivity of the surface water, land-use, and stream network were collected. After provision of digital maps, they were classified, weighted, and integrated through Boolean and Fuzzy operators. The result revealed almost 4.25% of the whole plain area is appropriate for GAR based on Boolean. Also, 4.79 and 17.94% of the plain area are suitable and rather favorable, respectively, based on Fuzzy. Finally, 34 locations were introduced with priorities A, B, and AB as being potentially suitable for GAR. The relationship between geomorphology and suitable areas for GAR based on Boolean and Fuzzy method indicated that the majority of these areas were located on colluvial fans units.

Identifying the water source for subsurface flow with deuterium and oxygen-18 isotopes of soil water collected from tension lysimeters and cores

• Soil water showed different residence time along the profiles. • Piston flow and preferential flow coexisted in the study Entisol. • The mobile soil water was the pre-event water who participated subsurface flow generation. • Rainwater only well mix with mobile soil water in the vadoze zone. • Bulk and lysimeter water showed significant differences in isotopic composition. The conventional identification of soil water with pre-event water limits deep insights into the involvement of stationary and mobile soil water in subsurface hydrological processes. In three tilled sloping field plots at a hilly area of southwestern China dominated by Entisols, soil water collected with a suction lysimeter was distinguished from the total soil water through an analysis of the stable isotopes deuterium and oxygen-18. Differences in the depth profile of soil water before and after storm events were observed and used to examine how rainwater mixes with soil water and to identify the source contribution of different fractions of soil water in subsurface flow generation. Only water in the 0–10 cm soil layer was significantly affected by evaporation and infiltration. Water in the top 5 cm layer of the soil exhibited the lowest residence time because a storm can replace a substantial proportion of the pre-event water. Soil water at the 10–20 cm depth showed the longest residence time, as indicated by its high proportion of pre-event water. The isotopic signatures demonstrated that piston flow and preferential flow coexisted in this soil. High antecedent soil water content and high rain intensity favor the formation of piston flow. The water collected with the suction lysimeter represented the mobile fraction of the pre-event water in the soil, which effectively participates in the generation of subsurface flow. Newly infiltrated rainwater did not well mix with stationary pre-event water in the soil. The use of recent rainfall to represent mobile soil water may provide a practical solution for overcoming the negative effect of the spatial heterogeneity of the isotopic composition of soil water on hydrograph separation results. Bulk soil water and lysimeter water showed significant differences in isotopic composition under low soil water content or in the top soil layer. Stable isotopes in bulk and lysimeter soil water should be monitored synchronously to reveal the sources and pathways of soil water and their contributions to the generation of subsurface flow in the vadose zone.

Leaching of Br−, metolachlor, alachlor, atrazine, deethylatrazine and deisopropylatrazine in clayey vadoze zone: A field scale experiment in north-east Greece

An extensive four-year research program has been carried out to explore and acquire knowledge about the fundamental agricultural practices and processes affecting the mobility and bioavailability of pesticides in soils under semi-arid Mediterranean conditions. Pesticide leaching was studied under field conditions at five different depths using suction cups. Monitoring of metolachlor, alachlor, atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), and bromide ions in soil water, as well as dye patterns made apparent the significant role of preferential flow to the mobility of the studied compounds. Irrespective to their adsorption capacities and degradation rates, atrazine, metolachlor and bromide ions were simultaneously detected to 160 cm depth. Following 40 mm irrigation, just after their application, both alachlor and atrazine were leached to 160 cm depth within 18 h, giving maximum concentrations of 211 and 199 μg L−1, respectively. Metolachlor was also detected in all depth when its application was followed by a rainfall event (50 mm) two weeks after its application. The greatest concentrations of atrazine, alachlor and metolachlor in soil water were 1795, 1166 and 845 μg L−1, respectively. The greatest concentrations of atrazine’s degradation products (both DEA and DIA) appeared later in the season compared to the parent compound. Metolachlor exhibited the greatest persistence with concentrations up to 10 μg L−1 appearing in soil water 18 months after its application. Brilliant blue application followed by 40 mm irrigation clearly depict multi-branching network of preferential flow paths allowing the fast flow of the dye down to 150 cm within 24 h. This network was created by soil cracks caused by shrinking of dry soils, earthworms and plant roots. Chromatographic flow of the stained soil solution was evident only in the upper 10–15 cm of soil.

Critical Review on the Parameters Influencing Soil-Water Characteristic Curve

The knowledge of unsaturated soil is indispensable for several hydrological and geoenvironmental problems such as permeation of water through vadoze zone, ground water recharge, and deciding irriga...