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Reactive transport codes for subsurface environmental simulation
Steefel, C.I. ; Appelo, C.A.J. ; Arora, B. ; Kalbacher, D. ; Kolditz, O. ; Lagneau, V. ; Lichtner, P.C. ; Mayer, K.U. ; Meeussen, J.C.L. ; Molins, S. ; Moulton, D. ; Shao, D. ; Simunek, J. ; Spycher, N. ; Yabusaki, S.B. ; Yeh, G.T. - \ 2015
Computational Geosciences 19 (2015)3. - ISSN 1420-0597 - p. 445 - 478.
variably saturated flow - dynamic leaching tests - fluid-rock interaction - porous-media - chemical-reactions - co2 sequestration - biogeochemical processes - geochemical speciation - preferential flow - heterogeneous aquifers
A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a high-level list of capabilities for each of the codes, along with a selective list of applications that highlight their capabilities and historical development.
Correction of the Vimoke–Taylor Concept Representing Drains in a Numerical Simulation Model
Heinen, M. - \ 2014
Vadose Zone Journal 13 (2014)10. - ISSN 1539-1663 - 9 p.
flood-irrigated field - hydraulic conductivity - water-flow - subsurface drains - preferential flow - soil - transport - equation - nitrate
Proper prediction of drain discharge using the single node Vimoke and Taylor approach in a numerical simulation model requires an additional correction factor. This correction factor was calibrated and dependent on node size, drain radius and the way of averaging the hydraulic conductivity. For a transient situation the additional correction factor resulted in higher groundwater levels and lower drain discharges. Drains are special internal or boundary conditions in numerical simulation models. Instead of approximating them by a hole surrounded by a very dense grid of finite elements, the single node or single element approach based on the theory of Vimoke and Taylor proposed in 1962 offers a good alternative. Several authors have suggested that the Vimoke and Taylor constant to adapt the hydraulic conductivity of the element representing the drain should be changed by a certain factor. However, different correction factors have been given. Here this correction factor is derived for a control volume finite element numerical simulation model for different ratios of the size of the control volume representing the drain and the effective drain radius. It is shown that this relationship is dependent on the way the hydraulic conductivity is averaged at the interfaces between the neighboring control volumes. The relationships were obtained by optimization against an analytical solution for a steady-state, saturated situation. By applying the additional correction to a hypothetical transient situation for four soil types it was shown that the application of the additional correction factor resulted in 3 to 13% lower drain discharges compared to uncorrected simulations. Consequently, higher groundwater levels of on average 2 to 4 cm were obtained when applying the additional correction. For situations where exact predictions of drain discharge are needed, typically when solute transport is considered, it is advised to make use of the additional correction. Model specific correction factors may be required.
Gedrag van verdroogde kades : fase B, C, D: onstaan en gevaar van krimpscheuren in klei- en veenkades
Akker, J.J.H. van den; Hendriks, R.F.A. ; Frissel, J.Y. ; Oostindie, K. ; Wesseling, J.G. - \ 2014
Wageningen : Alterra (Alterra-rapport 2473) - 87
bodemtypen - scheurvorming - dijken - bodemfysica - preferente stroming - bodemwater - stabiliteit - soil types - cracking - dykes - soil physics - preferential flow - soil water - stability
Het beschreven onderzoek in dit rapport is onderdeel van het onderzoeksproject ‘gedrag van verdroogde kades’ van het Hoogheemraadschap Delfland. Het onderzoek van Alterra is een bureau- en modelonderzoek en is gericht op scheuren door krimp, die ontstaan in lange perioden met droogte. Onderzocht zijn veenkaden en kleikaden op veen, met een accent op kleikaden omdat deze in Delfland het meeste voorkomen. Bij kleikaden lijkt het grootste risico preferente stroming via de scheuren te zijn. Bomen kunnen door hun diepe beworteling en grote verdamping een extra risico vormen. Langsscheuren in de kruin kunnen met water gevuld worden en dit kan resulteren in een bezwijkmechanisme. Dit is door Deltares nader onderzocht in een parallel rapport.
Comparison of two methods to assess heterogeneity of water flow in soils
Lichner, L. ; Dusek, J. ; Dekker, L.W. ; Zhukova, N. ; Fasko, P. ; Holko, L. ; Sir, M. - \ 2013
Journal of Hydrology and Hydromechanics 61 (2013)4. - ISSN 0042-790X - p. 299 - 304.
preferential flow - sandy soil - hydrophysical parameters - field experiment - loam - infiltration - movement
The heterogeneity of water flow and solute transport was assessed during radioactive tracer infiltration experiment in a black clay loam soil using modified methods to estimate the effective cross section (ECS) and the degree of preferential flow (DPF). The results of field and numerical experiments showed that these parameters characterized the heterogeneity of water flow in the soils unequivocally. The ECS decreases non-linearly and the DPF increases linearly with an increase of the bypassing ratio (ratio of macropore flow rate to total flow rate). The ECS decreased and the DPF increased with depth, which suggests an increase in the heterogeneity of water flow with depth. The plot of the DPF against ECS values calculated from the tracer experiment data was consistent with the relationship obtained by the numerical simulation assuming preferential flow in the neighbourhood of three probes.
Leaching of plant protection products to field ditches in the Netherlands : development of a drainpipe scenario for arable land
Tiktak, A. ; Boesten, J.J.T.I. ; Hendriks, R.F.A. ; Linden, A.M.A. van der - \ 2012
Bilthoven : National Institute for Public Health and the Environment (RIVM report 607407003/2012) - 106
bouwland - bodemchemie - drainage - uitspoelen - pesticiden - zware kleigronden - preferente stroming - modellen - waterverontreiniging - arable land - soil chemistry - leaching - pesticides - clay soils - preferential flow - models - water pollution
In the current Dutch authorisation procedure for calculating exposure of surface water organisms to plant protection products, deposition of drift is considered to be the only source. Drainage from agriclutural fields is being ignored. Because drainage may be an important source for exposure of water organisms, RIVM, Wageningen UR and the Board for the authorisation of plant protection products and biocides derived a new procedure in which drainage is included
A spatially distributed model of pesticide movement in Dutch macroporous soils
Tiktak, A. ; Hendriks, R.F.A. ; Boesten, J.J.T.I. ; Linden, A.M.A. van der - \ 2012
Journal of Hydrology 470-471 (2012)november. - ISSN 0022-1694 - p. 316 - 327.
clay soil - preferential flow - solute transport - hydraulic conductivity - unsaturated soils - water-flow - infiltration - simulation - rainfall - bromide
In the Netherlands, a spatially distributed version of the pesticide fate model PEARL is routinely used to assess the leaching potential of pesticides to groundwater. Recently, the model was modified to simulate the movement of pesticides to surface water. The peak concentration is considered to be the most important exposure endpoint for the ecotoxicological effect assessment for aquatic organisms. Macropore flow is an important driver for the peak concentration, so the leaching model PEARL was extended with a macropore module. Macropore parameters were derived from generally available soil data such as organic matter content and clay content using newly developed pedotransfer functions. These pedotransfer functions were constructed using a wide range of Dutch clayey soils. Results indicate a good correlation between these variables and soil structural parameters, which is due to the homogeneous mineralogical composition of Dutch clayey soils. Results of the spatially distributed modelling indicate that due to rapid transport through macropores, the concentration of pesticides in drainage water is generally higher in clayey soils than in light textured soils. In clayey soils, the boundary hydraulic conductivity and organic matter content were the most important drivers for the concentration in drainage water. Results further indicate that the concentration of pesticide in drainage water increases with increasing half-life and decreases with increasing sorption coefficient. However, the effect of these parameters is much less than obtained with the convection–dispersion equation because due to preferential flow most of the reactive part of the soil profile is bypassed.
Soil as a filter for groundwater quality
Keesstra, S.D. ; Geissen, V. ; Mosse, K. ; Piiranen, S. ; Scudiero, E. ; Leistra, M. ; Schaik, L. van - \ 2012
Current Opinion in Environmental Sustainability 4 (2012)5. - ISSN 1877-3435 - p. 507 - 516.
municipal waste-water - preferential flow - solute transport - mitigation strategies - lumbricus-terrestris - earthworm burrows - structured soils - land application - site preparation - vadose zone
The filtering function of soil is an important ecosystem service for groundwater and surface water protection. The efficiency of soils as a filter depends on the behaviour of pollutants in the soil and the hydrological transport processes. This paper aims to identify knowledge gaps in processes influencing pollutant behaviour in soils and their potential transport to groundwater. Currently most soil-filter function research is approached from two disciplines, one originating from agronomical/environmental sciences; one from more fundamental hydrological process research. Combining insights and approaches from both disciplines through collaboration could lead to better understanding of this complex system and enhance assessments of management strategy changes, both over the long term as well as in different climatic settings.
Pesticide transport pathways from a sloped litchi orchard to an adjacent tropical stream as identified by hydrograph separation
Duffner, A. ; Ingwersen, J. ; Hugenschmidt, C. ; Streck, T. - \ 2012
Journal of Environmental Quality 41 (2012)4. - ISSN 0047-2425 - p. 1315 - 1323.
climate-soil controls - open-fractured soil - hydrological processes - northern thailand - electrical-conductivity - conceptual examination - mountainous catchment - headwater catchment - preferential flow - isotopic tracers
This study was performed to identify the transport pathways of pesticides from a sloped litchi (Litchi chinensis Sonn.) orchard to a nearby stream based on a three-component hydrograph separation (baseflow, interflow, surface runoff). Dissolved silica and electrical conductivity were chosen as representative tracers. During the study period (30 d), 0.4 and 0.01% of the applied mass of atrazine and chlorpyrifos, respectively, were detected in the stream after 151 mm of rainfall. Baseflow (80–96%) was the dominant hydrological flow component, followed by interflow (3–18%) and surface runoff (1–7%). Despite its small contribution to total discharge, surface runoff was the dominant atrazine transport pathway during the first days after application because pesticide concentrations in the surface runoff flow component declined quickly within several days. Preferential transport with interflow became the dominant pathway of atrazine. Because chlorpyrifos was detected in the stream water only twice, it was not included in the hydrograph separation. A feature of the surface runoff pathway was the coincidence of pesticide and discharge peaks. In contrast, peak concentrations of pesticides transported by interflow occurred during the hydrograph recession phases. Stormflow generation and pesticide transport depended on antecedent rainfall. The combination of high-resolution pesticide concentration measurements with a three-component hydrograph separation has been shown to be a suitable method to identify pesticide transport pathways under tropical conditions.
Quantifying heterogeneous transport of a tracer and a degradable contaminant in the field, with snowmelt and irrigation
Schotanus, D. ; Ploeg, M.J. van der; Zee, S.E.A.T.M. van der - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 2871 - 2882.
well-structured soil - solute transport - water-flow - preferential flow - spatial variability - propylene-glycol - unsaturated zone - saturated soil - steady-state - nonequilibrium
To examine the persistence of preferential flow paths in a field soil, and to compare the leaching of a degradable contaminant with the leaching of a tracer, two field experiments were performed using a multi-compartment sampler (MCS). The first experiment was carried out during the snowmelt period in early spring, characterized by high infiltration fluxes from snowmelt. The second experiment was carried out in early summer with irrigation to mimic homogeneous rainfall. During the second experiment, the soil was warmer and degradation of the degradable contaminant was observed. For both experiments, the highest tracer concentrations were found in the same area of the sampler, but the leached tracer masses of the individual locations were not highly correlated. Thus, the preferential flow paths were stable between the two experiments. With a lower infiltration rate, in the second experiment, more isolated peaks in the drainage and the leached masses were found than in the first experiment. Therefore, it is concluded that the soil heterogeneity is mainly caused by local differences in the soil hydraulic properties, and not by macropores. With higher infiltration rates, the high and low leaching cells were more clustered. The leached masses of the degradable contaminant were lower than the leached masses of the tracer, but the masses were highly correlated. The first-order degradation rate and the dispersivity were fitted with CXTFIT; the first-order degradation rate was 0.02 d-1, and the dispersivity varied between 1.9 and 7.1 cm. The persistence of the flow paths during the experiments suggests soil heterogeneity as the driver for heterogeneous flow and solute transport in this soil. At the MCS scale, heterogeneous snowmelt did not seem to have much influence on the flow and solute paths
Heterogeneous water flow and pesticide transport in cultivated sandy soils : description of model concepts
Leistra, M. ; Boesten, J.J.T.I. - \ 2011
Wageningen : Alterra (Alterra-report 2182) - 64
zandgronden - pesticiden - uitspoelen - grondwater - simulatiemodellen - preferente stroming - sandy soils - pesticides - leaching - groundwater - simulation models - preferential flow
There is ample experimental evidence that complications in water flow and pesticide transport can occur in cultivated humic-sandy and loamy-sandy soils. As a result, pesticide leaching to groundwater and water courses can be higher than expected. We made an inventory of mechanistic/deterministic model concepts that may be suitable for simulating preferential water flow and pesticide transport in these soils. The convection-dispersion approach, the mobile-stagnant concept, the dual-velocity concept, the explicit description of horizontal diffusion, the soil column approach and a concept of finger flow are discussed. Only for comparatively simple concepts it is feasible to ever obtain the parameter values. Ideally, the data sets to be used for testing the models concepts should be detailed and complete. Discrimination between the validity of the model concepts requires the variation in the measuring results to be limited. Testing of the model concepts under various representative field conditions is needed, to gain confidence in their results.
Measurement and Computation of Movement of Bromide Ions and Carbofuran in Ridged HUmic-Sandy Soil
Leistra, M. ; Boesten, J.J.T.I. - \ 2010
Archives of Environmental Contamination and Toxicology 59 (2010)1. - ISSN 0090-4341 - p. 39 - 48.
preferential flow - irrigated potato - water - field - transport - aldicarb - stemflow
Water flow and pesticide transport in the soil of fields with ridges and furrows may be more complex than in the soil of more level fields. Prior to crop emergence, the tracer bromide ion and the insecticide carbofuran were sprayed on the humic-sandy soil of a potato field with ridges and furrows. Rainfall was supplemented by sprinkler irrigation. The distribution of the substances in the soil profile of the ridges and furrows was measured on three dates in the potato growing season. Separate ridge and furrow systems were simulated by using the pesticide emission assessment at regional and local scales (PEARL) model for pesticide behavior in soil–plant systems. The substances travelled deeper in the furrow soil than in the ridge soil, because of runoff from the ridges to the furrows. At 19 days after application, the peak of the bromide distribution was measured to be in the 0.1–0.2 m layer of the ridges, while it was in the 0.3–0.5 m layer of the furrows. After 65 days, the peak of the carbofuran distribution in the ridge soil was still in the 0.1 m top layer, while the pesticide was rather evenly distributed in the top 0.6 m of the furrow soil. The wide ranges in concentration measured with depth showed that preferential water flow and substance transport occurred in the sandy soil. Part of the bromide ion distribution was measured to move faster in soil than the computed wave. The runoff of water and pesticide from the ridges to the furrows, and the thinner root zone in the furrows, are expected to increase the risk of leaching to groundwater in ridged fields, in comparison with more level fields.
Parameterization of Macropore Flow Using Dye-Tracer Infiltration Patterns in the SWAP Model
Schaik, N.L.M.B. ; Hendriks, R.F.A. ; Dam, J.C. van - \ 2010
Vadose Zone Journal 9 (2010)1. - ISSN 1539-1663 - p. 95 - 106.
preferential flow - solute transport - system extremadura - scale variation - soil profiles - water - spain - methodology - hillslopes - catchment
Preferential flow is known to influence infiltration, soil moisture content distribution, groundwater response, and runoff generation. Various model concepts are used to simulate preferential flow. Preferential flow parameters are often determined by indirect optimization using outflow or discharge measurements, thereby providing limited insight into model performance concerning soil moisture distribution. In this study, we used a physically based macropore concept, embedded in the SWAP model, in combination with dye infiltration patterns to parameterize macropore infiltration for three locations in a catchment: hilltop, hillslope, and valley bottom. The model with the calibrated macropore parameters was applied and validated under natural field conditions, using detailed data on soil moisture content, rainfall, and discharge. The results show that the macropore model parameters can be optimized well to reproduce the dye-tracer infiltration patterns. The simulations of the dye patterns show much better results when macropore flow is included. Using the tracer infiltration patterns, however, the optimized maximum depth of macropores depends completely on the maximum depth of the stained area, while the macropores are known to extend deeper into the soil. Therefore, for long-term simulations, the wetting of deeper layers is too slow for the simulations both with and without macropores. Runoff production was better simulated with macropores. For the simulations without macropores, a higher lumped saturated conductivity was used; despite the resulting increased infiltration into the soil matrix, runoff generation remained far too high
Field-Scale Measurements for Separation of Catchment Discharge into Flow Route Contributions
Velde, Y. van der; Rozemeijer, J. ; Rooij, G.H. de; Geer, F.C. van; Broers, H.P. - \ 2010
Vadose Zone Journal 9 (2010)1. - ISSN 1539-1663 - p. 25 - 35.
hydrological pathways - preferential flow - surface-water - land-use - nitrate - soil - groundwater - dynamics - agriculture - uncertainty
Agricultural pollutants in catchments are transported toward the discharging stream through various flow routes such as tube drain flow, groundwater flow, interflow, and overland flow. Direct measurements of flow route contributions are difficult and often impossible. We developed a field-scale setup that can measure the contribution of the tube drain flow route to the total discharge toward the surface water system. We then embedded these field-scale measurements in a nested measurement setup to asses the value of field-scale measurements for interpretation of catchment-scale discharge and nitrate concentrations using a linear flow route mixing model. In a lowland catchment, we physically separated the tube drain effluent from the discharge of all other flow routes. Upscaling the field-scale flow route discharge contributions to the subcatchment and the catchment scale with a linear flow route mixing model gave a good prediction of the catchment discharge. Catchment-scale nitrate concentrations were simulated well for a heavy rainfall event but poorly for a small rainfall event. The nested measurement setup revealed that the fluxes at a single field site cannot be representative for the entire catchment at all times. However, the distinctly different hydrograph reaction of the individual flow routes on rainfall events at the field site made it possible to interpret the catchment-scale hydrograph and nitrate concentrations. This study showed that physical separation of flow route contributions at the field scale is feasible and essential for understanding catchment-scale discharge generation and solute transport processes
Preventie van preferente stroming in de zandgrond van een golfbaan
Oostindie, K. ; Dekker, L.W. ; Moore, D. ; Wesseling, J.G. ; Ritsema, C.J. - \ 2008
Stromingen : vakblad voor hydrologen 14 (2008)1. - ISSN 1382-6069 - p. 25 - 39.
zandgronden - bodemwater - golfbanen - preferente stroming - utrechtse heuvelrug - sandy soils - soil water - golf courses - preferential flow - utrechtse heuvelrug
Veel zandbovengronden met een grasvegetatie hebben waterafstotende eigenschappen. Deze hydrofobe eigenschappen komen naar voren als het vochtgehalte van de grond beneden een kritieke grens daalt. Na het bereiken van deze grens zal de infiltratiesnelheid van neerslag en beregeningswater sterk afnemen. De indringing van het water gaat dan ongelijkmatig en er ontstaan preferente stroombanen in de grond. Op golfbaan "De Pan" in Bosch en Duin onderzochten we de effecten van het toedienen van een surfactant op de bevochtiging en de variatie van het vochtgehalte van de toplaag in een fairway
Soil water repellency in an old and young pasture in relation to N application
Sonneveld, M.P.W. - \ 2008
Soil Use and Management 24 (2008)3. - ISSN 0266-0032 - p. 310 - 317.
sandy soil - preferential flow - moisture - management - movement - portugal - patterns
Ageing of pastures is likely to affect the degree of potential water repellency in the long term, whereas seasonal variation on a shorter term affects the actual repellency of soils. A 1-year study on two pastures of different ages was conducted on a sandy soil to assess changes in the degree of potential and actual water repellency in relation to different levels of applied nitrogen (N). Sampling was carried out on four dates (April, June, August and October) to determine soil moisture content and both potential and actual water repellency at three depths (0¿25, 25¿50 and 50¿75 cm). The relative number of potentially wettable samples for the young pasture (5 years) ranged from 64% (0¿25 cm) to 96% (25¿50 cm) to 100% (50¿75 cm). For the old pasture (38 years) this ranged from 29 to 66 to 94%. The transition zone in which topsoil samples could be either wettable or water repellent ranged from 18 to 23% (v/v) for the young pasture compared with a range from 29 to 32% (v/v) for the old pasture. Thus, ageing pastures may result in both moving as well as decreasing transition zones over time. A positive relationship between increased inputs of fertilizer N, higher DM yields, lower soil water contents and higher degrees of water repellency was found for the old pasture for the August series. This suggests that seasonal variation in water repellency can be further re-enforced through nutrient management.
Hydropedology: Synergistic integration of pedology and hydrology
Lin, H. ; Bouma, J. ; Pachepsky, Y. ; Western, A. ; Thompson, J. ; Genuchten, R. van; Vogel, H.J. ; Lilly, A. - \ 2006
Water Resources Research 42 (2006)5. - ISSN 0043-1397 - 13 p.
soil spatial variability - land-use history - environmental correlation - temporal stability - moisture patterns - preferential flow - organic-matter - water - scale - science
This paper presents a vision that advocates hydropedology as an advantageous integration of pedology and hydrology for studying the intimate relationships between soil, landscape, and hydrology. Landscape water flux is suggested as a unifying precept for hydropedology, through which pedologic and hydrologic expertise can be better integrated. Landscape water flux here encompasses the source, storage, flux, pathway, residence time, availability, and spatiotemporal distribution of water in the root and deep vadose zones within the landscape. After illustrating multiple knowledge gaps that can be addressed by the synergistic integration of pedology and hydrology, we suggest five scientific hypotheses that are critical to advancing hydropedology and enhancing the prediction of landscape water flux. We then present interlinked strategies for achieving the stated vision. It is our hope that by working together, hydrologists and pedologists, along with scientists in related disciplines, can better guide data acquisition, knowledge integration, and model-based prediction so as to advance the hydrologic sciences in the next decade and beyond.
Near-surface distributions of soil water and water repellency under three effluent irrigation scemes in a blue gum (Eucalyptus globulus) plantation
Thwaites, L.A. ; Rooij, G.H. de; Salzman, S. ; Allinson, G. ; Stagnitti, F. ; Carr, R. ; Versace, V. ; Struck, S. ; March, T. - \ 2006
Agricultural Water Management 86 (2006)1-2. - ISSN 0378-3774 - p. 212 - 219.
spatial variability - preferential flow - wetting patterns - pinus-radiata - sandy soils - portugal - hydrophobicity - management - australia - moisture
Water repellent soils are difficult to irrigate and susceptible to preferential flow, which enhances the potential for accelerated leaching to groundwater of hazardous substances. Over 5 Mha of Australian soil is water repellent, while treated municipal sewage is increasingly used for irrigation. Only if a critical water content is exceeded will repellent soils become wettable. To avoid excessive loss of water from the root zone via preferential flow paths, irrigation schemes should therefore aim to keep the soil wet enough to maintain soil wettability. Our objective was to monitor the near-surface water content and water repellency in a blue gum (Eucalyptus globulus) plantation irrigated with treated sewage. The plantation's sandy soil surface was strongly water repellent when dry. For 4 months, three rows of 15 blue gum trees each received no irrigation, three other rows received 50% of the estimated potential water use minus rainfall, and three more rows received 100%. During this period, 162 soil samples were obtained in three sampling rounds, and their water content (% dry mass) and degree of water repellency determined. Both high and low irrigation effectively wetted up the soil and eliminated water repellency after 2 (high) or 4 (low) months. A single-peaked distribution of water contents was observed in the soil samples, but the water repellency distribution was dichotomous, with 44% extremely water-repellent and 36% wettable. This is consistent with a threshold water content at which a soil sample changes from water repellent to wettable, with spatial variability of this threshold creating a much wider transition zone at the field scale. We characterized this transition zone by expressing the fraction of wettable samples as a function of water content, and demonstrated a way to estimate from this the wettable portion of a field from a number of water content measurements. To keep the plantation soil wettable, the water content must be maintained at a level at which a significant downward flux is likely, with the associated enhanced leaching. At water contents with negligible downward flux, the field is water repellent, and leaching through preferential flow paths is likely. Careful management is needed to resolve these conflicting requirements.
Quantifying minimum monolith size and solute dilution from multi-compartment percolation sampler data
Rooij, G.H. de; Cirpka, O.A. ; Stagnitti, F. ; Vuurens, S.H. ; Boll, J. - \ 2006
Vadose Zone Journal 5 (2006)5. - ISSN 1539-1663 - p. 1086 - 1092.
sandy vadose zone - spatial variability - heterogeneous soil - preferential flow - transport - dispersion - water - media
Preferential flow affects solute transport in natural soils, leading to high spatiotemporal variation of concentration. A multicompartment solute sampler (MCS), yielding multiple breakthrough curves at a given depth, can monitor tracer movement in a heterogeneous soil. We present a technique to estimate from MCS data whether a soil monolith is sufficiently large to capture preferential flow, which is a necessity for tracer breakthrough curves to be representative. For several soils, we estimate that an MCS should be larger than 0.1 to 0.2 m2. We also expand dilution theory to analyze the concentration variations of a tracer passing the control plane monitored by the MCS, in addition to the conventional plume spreading analysis. We characterize the set of locally observed breakthrough curves by the entropy-based dilution index. For given first and second-central moment, the spatially uniform log-normal breakthrough curve maximizes the dilution index. The ratio between observed and maximum dilution index is denoted reactor ratio. For a 300-compartment solute sampler, covering an area of 0.75 m2, we compute a reactor ratio of 0.665, compared with 0.04 for stochastic-convective and 1 for convective-dispersive transport. With a single, large collector the reactor ratio would be 0.958, severely underestimating concentration variations. Large collector areas are clearly inadequate to estimate dilution. Values of the dilution index and the reactor ratio for individual sampling compartments indicate efficient longitudinal mixing in most but not all cases, and considerable spatial variation of the leaching process.
Quantifying effects of soil heteogeneity on groundwater pollution at four sites in USA
Vuurens, S.H. ; Stagnitti, F. ; Rooij, G.H. de; Boll, J. ; Ling, Li ; LeBlanc, M. ; Ierodiaconou, D. ; Versace, V. ; Salzman, S. - \ 2005
Science in China Series C-Life Sciences 48 (2005)I. - ISSN 1006-9305 - p. 118 - 127.
sandy vadose zone - solute transport - preferential flow - metal contamination - water - variability - mechanism - behavior - model
Four sites located in the north-eastern region of the United States of America have been chosen to investigate the impacts of soil heterogeneity in the transport of solutes (bromide and chloride) through the vadose zone (the zone in the soil that lies below the root zone and above the permanent saturated groundwater). A recently proposed mathematical model based on the cumulative beta distribution has been deployed to compare and contrast the regions’ heterogeneity from multiple sample percolation experiments. Significant differences in patterns of solute leaching were observed even over a small spatial scale, indicating that traditional sampling methods for solute transport, for example the gravity pan or suction lysimeters, or more recent inventions such as the multiple sample percolation systems may not be effective in estimating solute fluxes in soils when a significant degree of soil heterogeneity is present. Consequently, ignoring soil heterogeneity in solute transport studies will likely result in under- or overprediction of leached fluxes and potentially lead to serious pollution of soils and/or groundwater. The cumulative beta distribution technique is found to be a versatile and simple technique of gaining valuable information regarding soil heterogeneity effects on solute transport. It is also an excellent tool for guiding future decisions of experimental designs particularly in regard to the number of samples within one site and the number of sampling locations between sites required to obtain a representative estimate of field solute or drainage flux
Effects of surfactant treatments on the wettability of a water repellent grass-covered dune sand
Dekker, L.W. ; Oostindie, K. ; Kostka, S.J. ; Ritsema, C.J. - \ 2005
Australian Journal of Soil Research 43 (2005)3. - ISSN 0004-9573 - p. 383 - 395.
preferential flow - wetting patterns - soil - severity
Copper is an important micronutrient and trace amounts are essential for crop growth. However, high concentrations of copper will produce toxic effects. Australia is increasingly developing production of crops in water repellent soils. Clay amendment, a common amelioration techniques used in Australia, has demonstrated agronomic benefits in increased crop or pasture production. The sorption and desorption of copper and the effect of clay treatment on copper behaviour in a water repellent soil collected from an experimental farm in South Australia is studied. We found that the water repellent soils amended with clay have an increased adsorption capacity of copper. Also the clay-amended soils had an increased ratio of specific sorption to total sorption of copper. The implications of this study to the sustainable agro-environmental management of water repellent soils is discussed