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• A screening tool named Colloids-Enhanced Transport (CET) model is developed. • The CET model is based on the enhanced transport of organic pollutants by soil colloids. • The CET model can predict the leaching potential of organic pollutants into groundwater. • The CET model can be used to derive soil quality standards or cleanup target levels. Modeling the fate and transport of organic pollutants at contaminated sites is critical for risk assessment and management practices, such as establishing realistic cleanup standards or remediation endpoints. Against the conventional wisdom that highly hydrophobic persistent organic pollutants (POPs) (e.g., polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons) in surface soils are essentially immobile, mounting evidence has demonstrated the potential of these contaminants leaching into the groundwater, due to enhanced transport by soil colloids. Here, we develop a Colloids-Enhanced Transport (CET) model, which can be used as a simple screening tool to predict the leaching potential of POPs into groundwater, as mediated by soil colloids. The CET model incorporates several processes, including the release of POPs-bearing colloids into the porewater, the vertical transport of colloids and associated POPs in the vadose zone, the mixing of POPs-containing soil leachate with groundwater, and the migration of POPs-bearing colloids in saturated zone. Thus, using parameters that can be easily obtained (e.g., annual rainfall, soil type, and common hydrogeological properties of the subsurface porous media), the CET model can estimate the concentrations of POPs in the saturated zone from the observed POPs concentrations in surface or shallow subsurface zones. The CET model can also be used to derive soil quality standards or cleanup endpoints by back-calculating soil concentrations based on groundwater protection limits. [Display omitted] [ABSTRACT FROM AUTHOR]

Bioretention is a water management practice that is increasingly being applied for runoff quality control. Although previous Bioretention studies have used some techniques to improve nutrient removal, some nutrients still leach out. Therefore, this study used Cascaded Bioretention (CB) by connecting three Bioretention columns in series. The planted Bioretention Column was retrofitted by adding a subsurface drainage module (SDM) below the gravel layer to create a dual saturated zone. This study aimed to investigate the effect of the number of treatments, vegetation, and modified saturated zone on enhancing nutrient removal from agricultural runoff and to understand nutrient removal mechanisms. The removal efficiencies of NH3-N, NO3-N, NO2-N, and TN improved to 89.8%, 49.7%, 49.2%, and 53.4%, respectively. The only negative removal was ON, which significantly decreased by incorporating vegetation and a modified saturated zone. Increasing the number of treatments significantly enhanced TN and ON while maintaining stable removal for other nitrogen compounds. However, phosphorus was less sensitive to increasing the number of treatments. Nitrogen removal could be enhanced by different removal processes such as nitrification, denitrification, mineralization, assimilation by plant uptake, and Anammox. However, phosphorus removal was less complicated, as adsorption and infiltration are likely to be the main removal mechanisms. [ABSTRACT FROM AUTHOR]

Understanding groundwater recharge mechanisms is essential for reliable groundwater recharge estimation for sustainable groundwater resource assessment and management, especially in arid and semiarid areas. In this study, chloride, together with stable isotopes (18O and 2H), in 1‐year rainfall, soil water from representative profiles, and groundwater samples, collected in the Ordos Plateau, northern China were analysed. Groundwater recharge was estimated using unsaturated‐ and saturated‐zone chloride mass balance (CMB). An equation that describes the relationship between chloride concentrations in saturated zone water (Csz) and soil water residence time (τ) was derived. With the help of the relationship, chloride concentrations in unsaturated zone water (Cuz) and in groundwater (Csz) can be used to uncover water flow and chloride transport in the unsaturated zone. The relationship between Csz and Cuz indicates that, the groundwater was recharged mainly by intense rainfall events. Small rainfall events did not lead to groundwater recharge but contributed to the flux of chloride to soil surface. Stable isotopic compositions of 18O and 2H provided corroborative evidence of the recharge processes. The relationship between Csz and τ indicates further that there is no source of chloride in the groundwater other than that from precipitation. Thus, Csz can give more reliable recharge estimates. Cuz was influenced by heavy rainfall‐induced runoff, run‐on and bypass flow events and cannot give reliable recharge estimates. However, if used jointly with Csz, Cuz can help to gain insights into recharge processes and yield groundwater recharge estimates with higher certainty. The outcomes of this study can assist for groundwater recharge investigation and assessment in regions where the assumptions and boundary conditions necessary for the correct application of the CMB method may not be met. [ABSTRACT FROM AUTHOR]

The presented procedure is designed to develop a system of models of the aeration zone and the saturated zone aimed to give a quantitative description of pollutant migration from a near-surface source to groundwater table and to the discharge zones of groundwater flow. The procedure is applied to an area with identified chloride pollution of groundwater. The source of pollution is a salt store, which was operated in the period 1967–2007. The concentration of chloride ion did not decrease after the liquidation of pollution source because of the formation of a secondary source (salination zone) in the aeration zone. Models of the aeration zone and the saturated zone were developed for the area under consideration. The model of the saturation zone was calibrated by monitoring data (groundwater table and chloride-ion concentration). The plume of chloride-ion in the groundwater flow was reproduced in the model in absolute concentrations. The calculations of pollutant migration in the aeration zone was calculated in relative concentrations. Simulation results were used to determine time intervals characterizing the stages of pollution plume formation over the operation time of the salt store, as well as the stages of plume degradation after the store was liquidated. The effect of model parameters for both zones on the results of transport calculations was evaluated to reveal the most significant among them. A series of model scenarios was considered (conservative and softer) to determine the variability of model forecasts. Retrospective model calculations, along with monitoring data, were used to obtain more accurate estimates of parameters, which characterize the deposits in the aeration zone. [ABSTRACT FROM AUTHOR]

The remediation of a polluted site relies, as a first stage, on the proper delineation of the contamination sources. In classical investigations, soil and water samples are collected throughout the field. These measurements allow a quantitative characterization of the gathered materials but only provide information about the medium in the vicinity of the points where they were collected. On the other hand, geophysical techniques can provide a quasi-continuous coverage of the investigated field. This paper describes a geophysical survey that was performed on an industrial site impacted by a chlorinated DNAPL. The precise location of the contamination was needed for the treatment of the saturated zone, while the unsaturated zone was remediated by general excavation of the sediments, followed by separate treatment. As this excavation allowed to get closer to the saturated zone, geophysical measurements were conducted at the bottom of the pit. Whereas Electrical Resistivity Tomography measurements only brought little information, Ground Penetrating Radar drew the remediation operations towards an area that preliminary point measurements had not identified as a possible source location.

The demand for clean and adequate water is rising rapidly with increasing population. This growing demand for water necessitates the measurement of the quantity and quality of water. Simulation modeling has become increasingly popular in the last two decades largely because of their predictive ability. This paper reviews the approaches for simulation modeling in groundwater resources management, focusing on models that have been used to simulate contaminant transport through the aquifer system. Recent research papers that have integrated the models for unsaturated and saturated zones have also been studied and described. Integrated models require assessment of the complex interactions between the groundwater zones and the movement of water and solute through them. Due to this, integrated models provide a more accurate modeling approach than models that have been independently developed for saturated and unsaturated zones. Application of such models is encouraged at the regional level to arrive at the best groundwater management decisions. Practitioner points: In the past few decades, modeling of contaminant transport in groundwater systems has seen tremendous applications.A number of models exist that independently simulate flow and solute transport in unsaturated and saturated zones.Recently, focus has been given on developing advanced coupled modeling approaches that require less inputs and run times. [ABSTRACT FROM AUTHOR]

Indigenous soil microbial communities play a pivotal role in the in situ bioremediation of contaminated sites. However, research on the distribution characteristics of microbial communities at various soil depths remains limited. In particular, there is little information on the assembly of microbial communities, especially those with degradation potential, in the vadose and saturated zones of hydrocarbon-contaminated sites. In this study, 18 soil samples were collected from the vadose zone and saturated zone at a long-term hydrocarbon-contaminated site. The diversity, composition, and driving factors of assembly of the soil bacterial community were determined by high-throughput sequencing analysis. Species richness and diversity were significantly higher in the vadose zone soils than in the saturated zone soils. Significant differences in abundance at both the phylum and genus levels were observed between the two zones. Soil bacterial community assembly was driven by the combination of pollution stress and nutrients in the vadose zone but by nutrient limitations in the saturated zone. The abundance of dechlorinating bacteria was greater in the saturated zone soils than in the vadose zone soils. Compared with contaminant concentrations, nutrient levels had a more pronounced impact on the abundance of dechlorinating bacteria. In addition, the interactions among dechlorinating bacterial populations were stronger in the saturated zone soils than in the vadose zone soils. These findings underscore the importance of comprehensively understanding indigenous microbial communities, especially those with degradation potential, across different soil layers to devise specific, effective in situ bioremediation strategies for contaminated sites. [Display omitted] • Significant differences exist in soil bacterial communities between the vadose zone and saturated zone. • Limited nutrients are key driving factors for bacterial community assembly in the saturated zone • More abundant dechlorinating bacteria exist in the saturated zone soils than the vadose zone soils • Nutrient levels have a greater impact on dechlorinating bacteria than contaminants • Interactions among dechlorinating bacteria are stronger in the saturated zone compared to the vadose zone. [ABSTRACT FROM AUTHOR]

Rainfall is one of the most significant natural factors for inducing landslides. The shallow saturated zone formed in slopes during rainfall is an important factor in inducing shallow landslides. In this paper, the characteristics and influencing factors of the saturated zone in soil slopes, and the relationship between the soil surface permeability coefficient and the rainfall intensity are analyzed. In this research, the equation that characterizes the rainfall intensity by the soil saturation is built based on the Mualem-van Genuchten model, which mathematically describes the soil water characteristics of unsaturated soils. Using this model, the target saturation of the slope surface during rainfall can be determined accurately, with an average deviation of − 0.008. Based on the equations, the innovative critical curve model of the rainfall intensity−time required to form the shallow saturated zone is established and calculated. The influence of the soil material, slope angle, rainfall intensity and antecedent rainfall on the critical curve for the shallow saturated zone is analyzed. The results indicate that for slopes of 30°~40°, it is easy for the shallow saturated zone to form, and the previous rainfall after more than 16 days has little impact on the critical curve. Furthermore, an innovative landslide prediction model, based on the critical curve for the shallow saturated zone and I-D modeling, is proposed to provide benchmarks for the prediction-specific characteristics of deep or shallow landslides, which is verified by the case of the Madiwan landslide. [ABSTRACT FROM AUTHOR]

One of the global geohazard issues discuss among scientists is soil liquefaction phenomenon. The incidents occurred at Palu in September 2018 and Aceh in December 2004, triggered soil liquefaction phenomenon which lead severe damages and lives. The common research on the geohazard issue include geotechnical methods (SPT and CPT) and geophysical methods (MASW and seismic). This study was conducted at Meuraxa district (Banda Aceh) and Baitussalam district (Aceh Besar) to introduce the capability of Electrical Resistivity Tomography (ERT) to predict the soil liquefaction phenomenon. The 2-D resistivity data were process using res2dinv inversion software to produce resistivity inversion models which then correlated with published results. The study identified that the resistivity values of 0.1 - 10 Ω m i s a soil saturated zone which affected by seawater intrusion and concludes that the study areas predicted by ERT have a high potential of soil liquefaction phenomenon to be occurred. [ABSTRACT FROM AUTHOR]

Greywater is an alternative water resource, having many favourable characteristics over stormwater or wastewater. In particular, it can be supplied consistently and generated close to desirable end-use applications. Although greywater is considered to contain a low level of contamination, treatment is still required before the end-use, and passive filtration such as biofiltration became a popular option due to its low maintenance and low energy consumption. To this end, a laboratory experiment was conducted with synthetic greywater over 12 months to test the influence of operational characteristics and design factors on pathogen removal from greywater. The role of plants types, saturated zone, and the absence/inclusion of antimicrobial material were tested in a total of 80 biofilter columns. The results showed that the biofilters obtained a median E. coli logarithmic removal of 3.0 across the tested configurations and produced quality of water that meets indoor non-potable use standard (NRMMC, 2006). Further, the infiltration rate and event size were found to significantly influence E. coli removal in greywater biofilters (ANOVA, p < 0.05). The presence of antimicrobial media also significantly improved E. coli removal (up to 1.4 log) compared to non-amended media (ANOVA, p < 0.05). Vegetation also played a significant role in removing E. coli (ANOVA < 0.05). This study successfully suggested the great potential for the application of biofilters to greywater treatment and identified key design factors for consideration prior to implementation. [ABSTRACT FROM AUTHOR]

Abstract A laboratory-scale vertical flow constructed wetland system was designed and monitored to compare nitrogen removal rates and pathways from both saturated and unsaturated zones under a hydraulic loading rate and influent total nitrogen concentration of 1.5 m3/m2.d and 508 mg/L respectively. Weekly measurements of the concentrations of nitrogen compounds, chemical oxygen demand, temperature, dissolved oxygen, oxidation-reduction potential, and hydrogen ion concentration were taken throughout the study. At the end of the experiments, PCR analysis of 16S rRNA gene sequencing was performed to identify microbial communities in the unsaturated and saturated parts of the system. The nitrogen compounds were removed from the system after 182 days, with similar total nitrogen removal efficiencies (94% and 93%) for the unsaturated and saturated zones respectively. Heterotrophic nitrification/aerobic denitrification was the major pathway responsible for the removal of nitrogen compounds. Adsorption into the gravel bed also contributed to ammonium removal. Proteobacteria were the dominant bacterial strains involved in nitrogen transformation and accounted for 80% of the total bacteria in the unsaturated zone and 60% in the saturated zone. With little difference in the concentration removal efficiencies of the unsaturated and saturated zones, a more effective design would be an entirely saturated wetland as the total mass removal of nitrogen depends on the water volume stored, which at full saturation in this design was seven times greater per unit wetland volume than the unsaturated zone. Highlights • Nitrogen decay is similar in unsaturated and saturated zones of the wetland. • Nitrate is lost by heterotrophic nitrification and aerobic denitrification. • Nitrite is also lost by heterotrophic nitrification and aerobic denitrification. • Ammonium loss occurs by heterotrophic nitrification and biofilm adsorption. • Saturated water content is seven times greater than the unsaturated water content. [ABSTRACT FROM AUTHOR]

Abstract: Rivers originating in the granitic highlands of seasonally dry central Argentina provide water to 2 million people. These highlands comprise a complex landscape where a matrix of outcropping rock hosts vegetated patches that vary in response to long‐term grazing and fire. We characterized water storage dynamics across 20 sites representing 6 vegetation‐soil conditions with similar mid‐upslope positions in the landscape. We measured temporal and spatial variability of water inputs (rain and fog) and water stored at the unsaturated and saturated zones. We found that rainfall was highly seasonal, but fog occurred year‐round, likely representing an extra water source in areas with complex vegetation structure. Moreover, fog seems to regulate evapotranspiration/topsoil water dynamics. Water was stored in the saturated zone only during the rainy season. Piezometric response to rainfall was rapid but transient (dropping an average 15 cm/day), possibly buffering peak stormflows, reducing sediment yield, and delivering subsurface water downslope for potential storing throughout the year. Spatially, a reduction in soil depth (from 100 up to 9 cm) and vegetation structure (from woodlands to stonelands), with a degradation of topsoil conditions for infiltration were accompanied by a decline in water storage at the unsaturated (from 32% up to 14%) and saturated (from 46.3 up to 0 cm) zones. Taken together, our results support the infiltration trade‐off hypothesis, which states that vegetation structure benefits fog interception, soil properties that enhance water infiltration, subsurface flow paths, and storage. Long‐term disturbances have likely triggered a degradation of the hydrological function of seasonal highlands in central Argentina. [ABSTRACT FROM AUTHOR]

The introduction of a saturated zone (SZ) has been recommended to address the issue of nitrogen removal fluctuation in the bioretention system, which is one of the most versatile low-impact development facilities for urban stormwater management. Nine experimental columns were used to characterize the nitrogen concentration variations over the outflow during wetting periods and in SZ during the antecedent drying periods (ADPs), as well as compare removal efficiencies of various nitrogen species in systems with different SZ depths under alternate drying and wetting conditions. Results indicated that NO3--N concentrations in the outflow showed quasi-logistic curve-shaped variations over time: being low (<0.5 mg/L) in the early process, sharply increasing thereafter, and finally flattening around 3.0 mg/L with NO3- leaching; NH4+-N and organic nitrogen (ON) concentrations were consistently low around 0.5 mg/L and 1.8 mg/L, respectively during the wetting periods. NH4+ removal efficiency in bioretention systems was consistently high around 80%, not varying with the increasing SZ depth; ON removal efficiency had a slight rise from 57% to 84% and NO3- removal efficiency was significantly enhanced from -23% to 62% with the SZ depth increasing from 0 to 600 mm. Deeper SZ could store more runoff and promote more denitrification of NO3- and mineralization of ON during the ADPs, providing more "old" water with low NO3- and ON concentrations for water exchange with "new" inflow of higher NO3- and ON concentrations during the wetting periods. The total nitrogen (TN) removal, a combined result of the instantaneous removal through adsorption and retention in the upper soil layer during the wetting periods and the gradual removal via denitrification and mineralization in SZ during the ADPs, was also improved by increasing the SZ depth; TN removal efficiency was elevated from 35% to 73% when the SZ depth increased from zero to 600 mm. [ABSTRACT FROM AUTHOR]

Plants play a critical role in the nutrient removal performance of stormwater biofilters. However, the influence of biofilter design on plant growth and subsequent implications for treatment performance are not well understood. A 12 month, laboratory-scale biofilter column experiment was conducted to investigate the response of Carex appressa to variations in biofilter design and implications for nutrient removal performance. Plant growth in Skye sand, a natural iron-coated sand with a strong capacity to immobilize phosphorus, was evaluated against a typical loamy sand filter media in biofilters with and without a saturated zone. Plant biomass correlated strongly with nutrient removal and was significantly greater in biofilters with a saturated zone, suggesting that inclusion of a saturated zone facilitates nutrient uptake. In the presence of a saturated zone, plants grown in Skye sand had a significantly higher specific root length, surface area and volume than plants grown in loamy sand, illustrating C. appressa ’ s ability to adapt root morphology to maintain growth under nutrient limited conditions. These root traits also correlated strongly with nutrient removal, suggesting that use of Skye sand in biofilters rather than loamy sand would be advantageous for nutrient removal. However, root adaptations, in particular increased etiolation, can make plants vulnerable to stressful environments (e.g. prolonged drying). Therefore, it is critical that a saturated zone be included in stormwater biofilters to increase growth and protect against drying. [ABSTRACT FROM AUTHOR]

Stormwater runoff greatly contributes to surface water pollution and deterioration of aquatic environment in urban areas. Biofilter, as low impact development (LID) technology, has been widely applied in controlling urban runoff pollution in recent years. A multi-layered biofilter with a saturated zone was employed in this study to test its removal efficiency of pollutants and the effect of saturation time on its performance with the real road runoff. Two groups of columns were built with different vegetations ( Zoysia matrella , ZM and a combination of Iris pseudacorus and Z. matrella , IZ). During a 2.5-month duration, five times of runoff dosing trials with collected stormwater were conducted at a load of 20–25 L day −1 . All filter systems had effective retention of particulate matters, with the turbidity removals of over 95%. The IZ group performed more efficiently than ZM systems in the removal of total phosphorus (TP), ammonia (NH 4 -N), nitrate (NO 3 -N) and turbidity. The mean removal of total nitrogen (TN) and TP was 49.8 ± 23.8% and 74.8 ± 9.9% in IZ group, and 42.6 ± 22.0% and 66.4 ± 12.2% in ZM group. Saturation time had significant effect on the removal of TN, TP and turbidity, whose concentrations declined with the saturation duration. The performances of biofilters were dynamic, as a function of media depth and retention time. The configuration of saturated zone and optimized depth of media layers (at least 0.75 m) can provide a favorable condition for nitrogen removal under random inflow condition. [ABSTRACT FROM AUTHOR]

Biochar has demonstrated promising performance as an amendment to biofilter soil media in removing fecal indicator bacteria (FIB) from simulated stormwater. However, there is no study that investigates its efficacy in treating natural stormwater runoff. Additional information, including the effects of antecedent dry period, microbial biofilm, and presence of a saturation zone on the performance of biochar-augmented biofilters are needed to inform their field implementation. This study uses laboratory column experiments to monitor FIB (enterococci and Escherichia coli ) and nutrient removal capacity of biochar-amended biofilters for 140 days using natural stormwater. Our study also investigates the effects of antecedent dry days (ADD) and the presence of a saturation zone (SZ) on the performance of lab-scale biochar-amended biofilters. The results suggest insignificant influence of the ADD and SZ on FIB removal performance, however biofilters with a SZ perform significantly better in removing nitrate-nitrogen compared to those without a SZ. In addition, it appears that the presence of biofilm augments nutrient removal capacity but reduces FIB removal capacity. Our observations indicate that biochar-amended biofilters are able to treat (to comply with recreational water quality standard for FIB) urban stormwater runoff for the duration of the experiment. Nitrate- and ammonium-nitrogen removal in the biologically aged biofilters is found to be 50–60% while the total dissolved phosphorus and the organic nitrogen removal is 20–30%. Our results inform full-scale design of biochar-amended biofilters in order to meet the total maximum daily load (TMDL) and municipal separate storm sewer system (MS4) permitting requirement for FIB and nutrients. [ABSTRACT FROM AUTHOR]

In the paper, we assess the mobility of copper and zinc in two sections, Granica and Kampinos, of the glacial and post-glacial sediments in the Kampinos National Park (Poland) and its buffer zone. The Granica section is practically devoid of carbonates and clay fraction, and the environment is markedly acidic. The other section, Kampinos, is characterized by a considerable content of carbonates (up to 20%) and clay fraction (up to 34%) with high sorption potential. The bonds of Zn and Cu cations with the solid phase occur mainly through adsorption and formation of salts, and through creation of chelated and complex connections. We found that, while sorption of Cu within the shallow groundwater zone under typical natural environment equilibrium conditions depends mainly on the content of the sorbing solid phase (i.e. organic matter and metal oxides and hydroxides), sorption of Zn within the shallow groundwater zone depends mainly on the fluctuating acidity and ionic strength of the groundwater, and to a lesser extent on the content and nature of the solid phase. The sorption process within the Kampinos section occurred predominantly on to three sorption media: clay fraction, organic matter and amorphous forms of Fe, Al and Mn. In the Granica section, because of the absence of clay fraction, sorption of the two metals occurred mainly with the organic matter and amorphous forms of Fe, Al and Mn. In addition, the sorption potential of the two metals in this section was low, because of the acidic pH of the environment, i.e. high availability of exchangeable hydrogen in the sorption complex. The concentrations of copper and zinc in the soil (S) were examined using both: the Lindsay and Norvell's and aqua regia methods. The methods of variable extraction capacity yielded very similar results for copper. In addition, the study found that the amounts of extracted zinc depended on the type of solution. The highest concentrations of zinc and copper were observed using the extraction with aqua regia. The results from determining zinc and copper concentrations (S) in the soil and rocks and the results of hydrochemical modelling show that the mobility of these two elements is highly limited by sorption processes; moreover, zinc is less effectively adsorbed than copper in these sections. [ABSTRACT FROM AUTHOR]

In the management of radionuclide release in the environment, the unsaturated zone could be a natural barrier to delay or to stop the radionuclide migration through the environment and to protect the groundwater from radiological risks. Thus, a suitable scientific evaluation of any radionuclide transport problems related to groundwater may to take into account the processes affecting flow through the unsaturated zone. In this work, an approach that involves the interactions between unsaturated zone and saturated zone both from hydrogeological and radionuclide transport point of view is proposed. This approach was tested developing a case study on an Italian nuclear site. The behavior of unsaturated zone as protective barrier for the groundwater was highlighted and identified as a fundamental aspect in the development of environmental analysis concerning the radionuclide transport into the environment. Promising results were found to improve the design of a radiological monitoring network. [ABSTRACT FROM AUTHOR]

Nitrate water pollution, which is mainly caused by agricultural activities, remains an international problem. It can cause serious long-term environmental and human health issues due to nitrate time-lag in the groundwater system. However, the nitrate subsurface legacy issue has rarely been considered in environmental water management. We have developed a simple catchment-scale approach to investigate the impact of historical nitrate loading from agricultural land on the nitrate-concentration trends in sandstones, which represent major aquifers in the Eden Valley, UK. The model developed considers the spatio-temporal nitrate loading, low permeability superficial deposits, dual-porosity unsaturated zones, and nitrate dilution in aquifers. Monte Carlo simulations were undertaken to analyse parameter sensitivity and calibrate the model using observed datasets. Time series of annual average nitrate concentrations from 1925 to 2150 were generated for four aquifer zones in the study area. The results show that the nitrate concentrations in ‘St Bees Sandstones’, ‘silicified Penrith Sandstones’, and ‘non-silicified Penrith Sandstones’ keep rising or stay high before declining to stable levels, whilst that in ‘interbedded Brockram Penrith Sandstones’ will level off after a slight decrease. This study can help policymakers better understand local nitrate-legacy issues. It also provides a framework for informing the long-term impact and timescale of different scenarios introduced to deliver water-quality compliance. This model requires relatively modest parameterisation and is readily transferable to other areas. [ABSTRACT FROM AUTHOR]

BIOCHLOR is a well-known simple tool for evaluating the transport of dissolved chlorinated solvents in groundwater, ideal for rapid screening and teaching. This work extends the BIOCHLOR model for the calculation of stable isotope ratios of carbon and chlorine isotopes in chloroethenes. An exact solution for the three-dimensional reactive transport of a chain of degrading compounds including sorption is provided in a spreadsheet and applied for modeling the transport of individual isotopes 12 C, 13 C, 35 Cl, 37 Cl from a constant source. The model can consider secondary isotope effects that can occur in the breaking of C Cl bonds. The model is correctly reproducing results for δ 13 C and δ 37 Cl modeled by a previously published 1-D numerical model without secondary isotope effects, and is also reproducing results from a microcosm experiment with secondary chlorine isotope effects. Two applications of the model using field data from literature are further given and discussed. The new BIOCHLOR-ISO model is distributed as a spreadsheet (MS EXCEL) along with this publication. [ABSTRACT FROM AUTHOR]

The injection of steam is a well-established technique for the thermally enhanced remediation of both unsaturated and saturated soils. Under saturated conditions, there is a limitation related to the thermal radius of influence (TRI) which results from the balance between viscous forces due to injection and buoyant forces due to the density difference between steam and water. Targeted preheating of the soil reduces the required time for a gaseous (steam) flow to be established after the beginning of a steam injection into the soil. Compared to non-preheated zones, the region where steam exists reaches a larger lateral extent before buoyancy eventually leads to a vertical breakthrough of the steam. This study investigates the impacts of preheating on the thermal radius of influence by considering different preheating scenarios with a full-complexity, 3D, non-isothermal numerical model including phase change. The achievable benefits of preheating are discussed; the potential costs of preheating are also considered. It is shown that preheating increases the TRI by more than 10 %. This is not much, but it suggests that preheating is an interesting option in cases where the increased TRI leads to a reduced number of injection wells required. [ABSTRACT FROM AUTHOR]

A simple, inexpensive method for extracting pore water from unsaturated soils, which uses a combination of immiscible fluid displacement, suction, and mechanical compression, is described. This method uses a squeezing chamber to contain the unsaturated sediments in aluminum core tubing to prevent exposure of the sediments and pore water to atmospheric O2 and subsequent oxidation reactions. Geochemical artifacts resulting from high-compression squeezing are prevented by maintaining the pressure applied during the squeezing at a minimum. Comparison of squeezed profiles with field measured profiles of pH, Eh (oxidation-reduction potential), alkalinity, and metal speciation indicates good agreement between these parameters using this method. Depending on the water content of the sediments, a range of water volumes (several millilitres to excess of 100 mL) can be extracted from a single core section 7.6 cm in diameter by 20 cm long. Pore water was produced immediately from sediments at near-saturated conditions, whereas several hours were required to obtain pore water from sediment with low moisture contents. Pore water was extracted from unsaturated sediments with as little as 6% volumetric moisture content. The squeezing technique provided water samples from both unsaturated and saturated sediments ranging from silt- to sand-sized particles. The method was applied successfully to collect pore waters from unsaturated sediments in neutral and acidic mine tailings; processed sands from oil sand operations, septic beds, agriculturally impacted sediments; and saturated soils from peat bogs, from wetlands, and at groundwater-surface interfaces. Le present article decrit une methode simple et peu dispendieuse pour expulser l'eau interstitielle de sols satures en utilisant une combinaison de deplacement de fluides immiscibles, de succion et de compression mecanique. Cette methode utilise une chambre de compression pour contenir les sediments non satures dans un tube carottier en aluminium afin d'empecher l'exposition des sediments et de l'eau interstitielle a l'oxygene de l'atmosphere et ainsi prevenir des reactions subsequentes d'oxydation. Des artefacts geochimiques, decoulant d'une compression elevee, sont evites en gardant l'application de la pression durant la compression a un minimum. Une comparaison des profils compresses avec des mesures sur le terrain du pH, de l'Eh, de l'alcalinite et de la speciation des metaux indique une bonne correlation entre ces parametres lorsque cette methode est utilisee. Selon la teneur en eau des sediments, une grande plage de volumes d'eau (plusieurs mL a plus de 100 mL) peut etre extraite d'un segment de carotte de 7,6 sur 20 cm. L'eau interstitielle a ete retiree immediatement des sediments presque satures alors que plusieurs heures etaient requises avant d'obtenir l'eau interstitielle des sediments a faible teneur en eau. De l'eau interstitielle a ete extraite de sediments non satures contenant aussi peu que 6 % d'humidite volumique. La technique de compression a donne des echantillons d'eau a partir de sediments satures et non satures et dont la granulometrie variait de silt a sable. La methode a ete appliquee avec succes pour extraire l'eau interstitielle de sediments non satures dans des residus miniers neutres et acides, de sables traites provenant des operations de sables bitumineux, de champs d'epuration, de sediments agricoles perturbes et de sols satures provenant de tourbieres, de milieux humides et d'interfaces eau souterrainesurface. [Traduit par la Redaction], Introduction Understanding geochemical processes in the unsaturated zone (vadose zone) is a fundamental aspect of hydrogeology studies. The vadose zone is an important component of many aspects of hydrogeology, including [...]

Nitrate is necessary for agricultural productivity, but can cause considerable problems if released into aquatic systems. Agricultural land is the major source of nitrates in UK groundwater. Due to the long time-lag in the groundwater system, it could take decades for leached nitrate from the soil to discharge into freshwaters. However, this nitrate time-lag has rarely been considered in environmental water management. Against this background, this paper presents an approach to modelling groundwater nitrate at the national scale, to simulate the impacts of historical nitrate loading from agricultural land on the evolution of groundwater nitrate concentrations. An additional process-based component was constructed for the saturated zone of significant aquifers in England and Wales. This uses a simple flow model which requires modelled recharge values, together with published aquifer properties and thickness data. A spatially distributed and temporally variable nitrate input function was also introduced. The sensitivity of parameters was analysed using Monte Carlo simulations. The model was calibrated using national nitrate monitoring data. Time series of annual average nitrate concentrations along with annual spatially distributed nitrate concentration maps from 1925 to 2150 were generated for 28 selected aquifer zones. The results show that 16 aquifer zones have an increasing trend in nitrate concentration, while average nitrate concentrations in the remaining 12 are declining. The results are also indicative of the trend in the flux of groundwater nitrate entering rivers through baseflow. The model thus enables the magnitude and timescale of groundwater nitrate response to be factored into source apportionment tools and to be taken into account alongside current planning of land-management options for reducing nitrate losses. [ABSTRACT FROM AUTHOR]

Common occurrence of copper and zinc in groundwater and their diverse mobility in the environment make these metals sensitive indicators of industrial and municipal pollution of freshwaters. An analysis of the collected data allowed for a description of the factors and processes that induce changes in the concentration of these metals in the soil, rock and groundwater. Sorption, ion exchange and oxidation–reduction processes, dissolution and precipitation of minerals, and reactions involving organic matter significantly affected the mobility of copper and zinc. The study employed hydrogeochemical methods to obtain comprehensive interpretative data. Its results showed that the variability of the composition of exchangeable cations was due to instability of chemical composition of precipitation. Different activities of Cu and Zn in the solution introduced into the rocks led to the establishment of new quasi-equilibrium states between the adsorbent and the adsorbate. At very low copper and zinc concentrations in groundwater, zinc was more easily retained in the solid phase, and it was more difficult to extract. In contrast, a laboratory static batch experiment utilizing high concentrations of the elements in the solutions showed their different behavior. The sorption of copper occurred more easily than the sorption of zinc, as evidenced by the study results and the calculated parameters of sorption maximum, binding constant, and degree of surface coverage of the solid phase by adsorbed copper and zinc according to a single Langmuir equation. [ABSTRACT FROM AUTHOR]

Computer solutions Multiphysics 3.5a software was used for simulating the two-dimensional copper migration including sorption process through the saturated zone of the soil in the presence of permeable reactive barrier for equilibrium condition. The 1:3 mixture of waste foundry sand and Kerbala's sand was used as filling material for this barrier. The waste foundry sand was represented the reactivity material, while Kerbala's sand used to increase the permeability of reactive barrier only. However, Fourier transform infrared analysis proved that the carboxylic and alkyl halide groups are responsible for the sorption of copper onto waste foundry sand. Batch tests have been performed to characterize the equilibrium sorption properties of the waste foundry sand and Kerbala's sand mix in copper-containing aqueous solutions. Numerical and experimental results proved that the permeable reactive barrier plays a potential role in the restriction of the contaminant plume migration. Also, predicted results showed that the thicker barrier is better than the thinner ones in copper treatment, and this barrier saturates with contaminant as a function of the travel time. However, a good agreement between the predicted and experimental results was recognized with mean error not exceeded 10 %. [ABSTRACT FROM AUTHOR]

The paper presents the simulation of 226Ra radionuclides transfer through the saturated zone of the site of Baita Bihor National Radioactive Waste Repository (NRWR), through a conceptual model of double porosity media. The effect of a continuous radioactive source located in repository was simulated. The radionuclides transfer simulation was carried out using the Toth model, the piezometric head is equal with the water level from the rivers. The area of radioactive influence of the repository, at the surface and at depth, was established. [ABSTRACT FROM AUTHOR]

Summary Riparian zones are considered potential hotspots of denitrification because they allow for the confluence of necessary electron acceptors (nitrate) and donors (carbon) via hydrologic flowpaths in low oxygen (reducing) conditions. While riparian areas have received considerable research attention, other soils prone to saturation have similar physicochemical characteristics but are less frequently studied. We quantified in situ denitrification rates in the shallow saturated zone, a dynamic portion of the landscape, across a range of hydroperiodicities, i.e., frequencies and durations of saturated conditions, as characterized by a topographic index in a small mixed land-use headwater catchment in central New York State. We found a strong positive relationship between topographic index and denitrification, indicating that the highest rates of denitrification occur in the relatively small portion of the landscape prone to saturation. We used the resulting relationship to distribute denitrification rates across the catchment and estimate denitrification fluxes from the shallow saturated zone. While the highest rates of denitrification were observed in wetter portions of the landscape, including riparian zones, we found that the shallow saturated zone beneath drier upland soils contributed to a larger portion of whole-catchment denitrification due to a larger areal extent. A topographic index-denitrification model is a promising and simple tool that allows for scaling of in situ denitrification rates across the landscape and provides insight into the spatial organization of denitrification at the catchment scale. [ABSTRACT FROM AUTHOR]

Biofilters have been shown to effectively treat stormwater and achieve nutrient load reduction targets. However, effluent concentrations of nitrogen and phosphorus typically exceed environmental targets for receiving water protection. This study investigates the role of filter media, vegetation and a saturated zone (SZ) in achieving co-optimised nitrogen and phosphorus removal in biofilters. Twenty biofilter columns were monitored over a 12-month period of dosing with semisynthetic stormwater. The frequency of dosing was altered seasonally to examine the impact of hydrologic variability. Very good nutrient removal (90% total phosphorus, 89% total nitrogen) could be achieved by incorporating vegetation, an SZ and Skye sand, a naturally occurring iron-rich filter medium. This design maintained nutrient removal at or below water quality guideline concentrations throughout the experiment, demonstrating resilience to wetting-drying fluctuations. The results also highlighted the benefit of including an SZ to maintain treatment performance over extended dry periods. These findings represent progress towards designing biofilters which co-optimise nitrogen and phosphorus removal and comply with water quality guidelines. [ABSTRACT FROM AUTHOR]

Highlights: [•] Denitrification rates were highly correlated to soil saturation frequency as described by the soil topographic index. [•] Denitrification from seasonally saturated soils accounted for about half of the total nitrogen imbalance in this headwater catchment. [•] Denitrification rates from riparian areas were high but only accounted for about 10% of the total nitrogen imbalance. [ABSTRACT FROM AUTHOR]

The quantification of the natural oxidant demand (NOD) of aquifer materials is required to estimate the fate of reagents injected into contaminated aquifers during in situ chemical oxidation applications. Three push-pull tests were conducted at a horizontal spacing of 12-20 m within an uncontaminated region of the saturated zone in the Canadian Forces Base Borden aquifer located near Alliston, Ont., Canada to estimate the NOD for permanganate. Each test contacted a minimum of 270 kg of aquifer material. Upper estimates of NOD values from the three tests were 0.51-0,75 g/kg based on the initial mass of aquifer material contacted, and lower estimates were 0.29-0.42 g/kg based on additional aquifer material mass contacted during the drift or reaction phase. These results compared favorably to NOD values determined from bench-scale tests with high solids mass to solution volume ratios. If design and operational concerns can be overcome, the push-pull test offers significant advantages over the variety of bench-scale testing methods currently used to determine the NOD of aquifer materials. CE Database subject headings: Ground water; Oxidation; Soil treatment; Water reclamation; Wells; Canada.

This manuscript addresses the topic of transverse dispersion and its impact on the behavior of the saturated zone below Yucca Mountain, a site that had been proposed for a US nuclear waste repository. Guided by a review of relevant observations of dispersion in similar formations, this study evaluates the importance of uncertainty in dispersion, particularly dispersion transverse to the mean transport direction, on metrics of interest to the Yucca Mountain risk assessment. Although as expected, larger values of transverse dispersivity lead to greater spreading of the plume in directions orthogonal to the mean flow direction, a corresponding sensitivity is not observed to the travel time statistics of the breakthrough curve at the compliance boundary. Thus, when a risk assessment is based on contaminant mass flux at compliance well or 'fence line' downstream from the source, as in the Yucca Mountain case, transverse dispersion may be of secondary importance to other parameters that more directly impact travel times. This result is in contrast to systems in which reactive transport processes are important to the attenuation of the plume, in which case transverse dispersion and mixing may be expected to play a dominant role in controlling the reaction rates and contaminant concentrations in the plume. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rainfall-runoff experiments and simulations were conducted on a hillslope system. [•] A saturated area formed at the slope toe, rose to the surface and expanded upslope. [•] Rainfall intensity affected surface runoff but not the maximum subsurface discharge. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional finite volume model to predict multi-species reactive transport processes in the saturated zone of a simulated semi-confined aquifer. A multipurpose commercial software called PHOENICS was used to solve model equations numerically. Capability of the present model was first confirmed using experimental data and the results obtained by a published one-dimensional finite element reactive transport model by other researchers taking different scenarios into consideration. The model was then expanded to a two-dimensional case to simulate reactive transport of BTX compounds with discontinuous source in the saturated zone of the groundwater flow system. In addition to the physical transport processes, the two-dimensional model also incorporates linear and nonlinear adsorption isotherms, first order and Monod kinetics. The two-dimensional model considers both static and dynamics modes into account. The results show that considering chemical reactions during reactive transport of contaminants could successfully predict the contaminated zone. The results of such studies can be used for monitoring of contaminated areas, designing methods to control pollution transport, and minimize its harmful effects on aquifer systems. [ABSTRACT FROM AUTHOR]

The aquifer Westliches Leibnitzer Feld, Austria, is a significant resource for regional and supraregional drinking water supply for more than 100,000 inhabitants, but the region also provides excellent agricultural conditions. This dual use implicates conflicts (e.g., non-point source groundwater pollution by nitrogen leaching), which have to be harmonized for a sustainable coexistence. At the aquifer scale, numerical models are state-of-the-art tools to simulate the behavior of groundwater quantity and quality and serve as decision support system for implementing groundwater protecting measures. While fully and iteratively coupled simulation models consider feedback between the saturated and unsaturated zone, sandy soil conditions and groundwater depths beneath the root zone allow the use of a unidirectional sequential coupling of the unsaturated water flow and nitrate transport model SIMWASER/STOTRASIM with FEFLOW for the investigation area. Considering separated inputs of water and nitrogen into groundwater out of surface water bodies, agricultural, residential and forested areas, first simulation results match observed groundwater tables, but underestimate nitrate concentrations in general. Thus, multiple scenarios assuming higher nitrogen inputs at the surface are simulated to converge with measured nitrate concentrations. Preliminary results indicate that N-input into the groundwater is strongly dominated by contributions of agricultural land. [ABSTRACT FROM AUTHOR]

The article presents research on the determination of organic carbon content feasibility derived from vermicompost and empty bed contact time (EBCT) on total nitrogen (TN) removal in saturated zone. The study demonstrates the significance of the organic carbon source amount and EBCT as design criteria for the removal of optimum nitrogen. It notes that more labile carbon sources help support better rates for NT removal.

Abstract: Nitrogen excess is a key trigger for eutrophication of water bodies. Stormwater can be an important N source in urban environments and thus requires effective treatment. Stormwater biofilters can remove a wide range of pollutants. However, removal of N is often insufficient due to a lack of denitrification in freely drained biofilters. We tested whether existing stormwater biofilters with poor N removal could be enhanced if a saturated zone is retrofitted to create anaerobic conditions for effective denitrification. We evaluated this by measuring removal of nitrogen, phosphorus and metals in retrofitted biofilters using laboratory mesocosms. For over 18 months five replicates of typical biofiltration configurations, that include freely draining 690mm deep loamy sand media above a 140mm deep transition layer and a 70mm gravel layer planted with popular plant species (Dianella revoluta, Microlaena stipoides and Carex appressa), were tested for typical operational conditions. The biofilter columns planted with D. revoluta and M. stipoides showed poor N removal, while biofilters planted with C. appressa were performing well. All columns were then retrofitted with a 450mm deep saturated zone, and testing continued using the same operational conditions. After retrofitting the saturated zone, NO x removal was significantly increased (mean increase: 370% for Dianella and 180% for Microlaena) which enhanced overall N removal. TP removal was less efficient after retrofitting the saturated zone due to presence of organic matter in the filter media within the saturated zone. The removal of metals was not affected in practical terms, despite some statistically significant effects. The results of this study suggest that retrofitting a saturated zone in existing standard biofilters should be recommended if the existing filter has inadequate N removal and if N discharges pose a potential threat to the receiving environment. [Copyright &y& Elsevier]

Abstract: Biofiltration is a technology applied to treat urban stormwater runoff that transports various pollutants, including pathogens. However, the pathogen removal performance of biofiltration systems remains unknown. A laboratory study was conducted to investigate the removal of three indicator organisms (Clostridium perfringens, Escherichia coli, and F-RNA coliphages) by biofilters. The influence of a range of factors was investigated: presence of vegetation, depth and types of filter media, presence of a saturated zone at the base of the biofilter, and intermittent wetting and drying conditions. The mean removal of C. perfringens and F-RNA coliphages by all biofilter designs exceeded 3log. E. coli removal during wet periods, however, was much lower (mean 2log). Furthermore, antecedent drying decreased the E. coli removal efficiency significantly (p <0.05). Drying might induce fine fissures or macropore formation in filter media thus reduced retention of microbes. This effect may be more obvious in vegetated designs due to evapotranspiration induced moisture loss. Introducing a saturated zone and carbon source at the base of the filter eliminated such negative effects of drying on E. coli removal. The effluent from biofilters with a saturated zone and carbon source met the recommended water quality for secondary contact recreational water use in relation to E. coli. [Copyright &y& Elsevier]

Archaeological, biological, and geochemical investigations of soil sample series from a section and five boreholes have been studied to evaluate the state of preservation at the time of investigation and the preservation conditions of urban archaeological deposits from medieval Oslo, Norway. Focus has been put on the most fragile deposits in the unsaturated and fluctuation zones. Even with limited investigations, it is possible to assess the archaeological conservation state and the preservation conditions. Further work should focus on interpreting measured results and on mitigation strategies. [ABSTRACT FROM AUTHOR]

Disturbed soil columns, 5.8 cm in diameter and 25 cm in length, were used as a basic model to simulate the movement of carbofuran in rice field soil under saturated conditions. Bioaugmentation using a specific carbofuran degrader, Burkholderia sp. PCL3, in free and immobilized cell forms and biostimulation using rice straw as organic amendment were applied with the aim of enhancing the degradation of carbofuran in soil and to prevent the movement of carbofuran along with the flow through. In the abiotic control and the treatment with only indigenous microorganisms, the mass recovery percentage of carbofuran in the effluent was 52.1 and 22.5%, respectively. The application of bioaugmentation or biostimulation significantly enhanced carbofuran degradation in soil and reduced the movement of carbofuran as indicated by a low mass recovery percentage of carbofuran in the effluent of 14.6-15.5%. A low efficiency of carbofuran removal was obtained from the soil column with bioaugmentation together with biostimulation treatments in which the mass recovery percentage of carbofuran in the effluent was in the range of 22.1-22.6%. Sorption of carbofuran to soil, rice straw and corncob, formation of carbofuran metabolite and colony forming unit (CFU) and pH variation with the time were also investigated during column operation. [ABSTRACT FROM AUTHOR]

The hydrochemical response at springs in the drainage area of the Sierra del Rey-Los Tajos carbonate aquifer (province of Málaga, southern Spain) was monitored in order to determine the hydrogeological functioning of this aquifer. Analysis of the most important chemical parameters, using methodologies such as the temporal evolution of chemical components, principal component analysis and discriminant factorial analysis revealed that the high level of hydrochemical heterogeneity to be found in this discharge zone, in addition to particular spatial and temporal factors, is responsible for the mineralisation of the spring water. Sampling in karst systems where discharge occurs by several springs should take into account the hydrochemical variability of them; otherwise conclusions about the hydrological functioning of aquifers deduced from mixture of spring waters can be inaccurate. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional models of hydraulic conductivity and porosity are essential to understand and simulate groundwater flow in heterogeneous geological environments. However, considering the inherent limitations of traditional hydrogeological field methods in terms of resolution, alternative field approaches are needed to establish such 3-D models with sufficient accuracy. In this study, we developed a workflow combining 3-D structural information extracted from ground penetrating radar (GPR) images with 1-D in situ physical-property estimates from direct-push (DP) logging to construct a 3-D hydrostratigraphic model. To illustrate this workflow, we collected an ∼70m×90m 100MHz 3-D GPR data set over a shallow sedimentary aquifer system resolving six different GPR facies down to ∼15m depth. DP logs of the relative dielectric permittivity, the relative hydraulic conductivity, the cone resistance, the sleeve friction and the pore pressure provided crucial data (1) to establish a GPR velocity model for 3-D depth migration and to check the time-to-depth conversion of the GPR data, and (2) to construct a 3-D hydrostratigraphic model. This model was built by assigning porosity values, which were computed from the DP relative dielectric permittivity logs, and DP relative hydraulic conductivity estimates to the identified GPR facies. We conclude that the integration of 3-D GPR structural images and 1-D DP logs of target physical parameters provides an efficient way for detailed 3-D subsurface characterization as needed, for example, for groundwater flow simulations. [Copyright &y& Elsevier]

Summary: From analysis of the hydrodynamic and hydrochemical responses of karst springs, it is possible to know the behaviour of the aquifers they drain. This manuscript aims to contribute to the characterization of infiltration process, and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers, using natural hydrochemical tracers. Thus, chemical components together with temperature and electrical conductivity (both punctual and continuous records) have been monitored in three springs which drain Alta Cadena carbonate aquifer, Southern Spain. An evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal. One of these springs responds rapidly to precipitation (conduit flow system), due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone, both of which play a similar role in the functioning of the spring. Another spring responds to precipitation with small increases in water flow, somewhat lagged, because the aquifer has a low degree of karstification, even in the unsaturated zone, which seems to influence its functioning more strongly than does the saturated zone. The third spring drains a sector of the aquifer with a moderately developed degree of karstification, one that is intermediate between the other two, in which both the unsaturated zone and the saturated zone participate in the functioning of the spring, but with the latter zone having a stronger influence. These three springs show different hydrogeological functioning although they are in similar geological and climatic contexts, which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas. [ABSTRACT FROM AUTHOR]

A tree can partition rainfall into throughfall and stemflow (SF), causing water to be funneled around the tree base, and can preferentially divert rainwater in soil layers, causing water to be funneled around tree roots. To determine the effects of each on soil water dynamics, we compared soil water dynamics around a tree on a hillslope on the basis of 2 years of field observations before (SF period) and after (non-SF period) intercepting the stemflow of the tree. Additionally, two sprinkling experiments were conducted using different dye tracers to separately indentify infiltration pathways derived from throughfall and stemflow. The observation results in the SF period showed irregular variations in soil water content, high soil water storage, and significant saturated zone development in the downslope region from the tree, which were attributed to stemflow concentrated on the downslope side of the tree. Although dramatic variations in soil water dynamics disappeared in the non-SF period, asymmetrical soil water response patterns were also observed, which were mainly attributed to root-induced bypass flow. Focusing on the downslope region in the SF and non-SF periods, the frequency of saturated zone generation at the soil-bedrock interface decreased from 58% to 16%, but the frequency of bypass flow occurrence varied little. Saturated zone generation at the soil-bedrock interface underneath the tree in both the SF and non-SF periods suggests that trees are key locations for rainfall infiltration and that tree-induced saturated zone generation should be considered carefully, even in conditions without stemflow supply. [ABSTRACT FROM AUTHOR]

3H-3He measurements constitute a well-established method for the determination of the residence time of young groundwater. However, this method has rarely been applied to karstified aquifers and in particular to drip water in caves, despite the importance of the information which may be obtained. Besides the determination of transfer times of climate signals from the atmosphere through the epikarst to speleothems as climate archives, 3H-3He together with Ne, Ar, Kr, Xe data may also help to give new insights into the local hydrogeology, e.g. the possible existence of a perched aquifer above a cave. In order to check the applicability of 3H-3He dating to cave drips, we collected drip water samples from three adjacent caves in northwestern Germany during several campaigns. The noble gas data were evaluated by inverse modelling to obtain recharge temperature and excess air, supporting the calculation of the tritiogenic 3He and hence the 3H-3He age. Although atmospheric noble gases were often found to be close to equilibrium with the cave atmosphere, several drip water samples yielded an elevated 3He/4He ratio, providing evidence for the accumulation of 3He from the decay of 3H. No significant contribution of radiogenic 4He was found, corresponding to the low residence times mostly in the range of one to three years. Despite complications during sampling, conditions of a perched aquifer could be confirmed by replicate samples at one drip site. Here, the excess air indicator ΔNe was about 10 %, comparable to typical values found in aquifers in mid-latitudes. The mean 3H-3He age of 2.1 years at this site presumably refers to the residence time in the perched aquifer and is lower than the entire transit time of 3.4 years estimated from the tritium data. [ABSTRACT FROM AUTHOR]