Solute transport in soil
Zee, S.E.A.T.M. van der; Leijnse, A. - \ 2013
In: Environmental sciences: soil processes and current trends in quality assessment / Hernandez Soriano, M.C., Rijeka, Croatia : InTech - ISBN 9789535110293 - p. 33 - 86.
bodemchemie - waterstroming - bodemoplossing - modellen - soil chemistry - water flow - soil solution - models
Solute transport is of importance in view of the movement of nutrient elements, e.g. towards the plant root system, and because of a broad range of pollutants. Pollution is not necessarily man induced, but may be due to geological or geohydrological causes, e.g. in the cases of pollution with arsenic, and salt. For the polluting species, a distinction can be made between dissolved and immiscible, and between conservative and reactive. Dissolved pollutants (aqueous phase pollutants) will spread with the groundwater due to groundwater flow, diffusion and dispersion.
Determination of free Zn2+ concentration in synthetic and natural samples with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Techniques)
Chito, D. ; Weng, L.P. ; Galceran, J. ; Companys, E. ; Puy, J. ; Riemsdijk, W.H. van; Leeuwen, H.P. van - \ 2012
Science of the Total Environment 421-422 (2012). - ISSN 0048-9697 - p. 238 - 244.
dissolved organic-matter - metal-ion concentrations - humic-acid - electroanalytical technique - lolium-perenne - soil solution - trace-metals - speciation - binding - waters
The determination of free Zn2+ ion concentration is a key in the study of environmental systems like river water and soils, due to its impact on bioavailability and toxicity. AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Technique) are emerging techniques suited for the determination of free heavy metal concentrations, especially in the case of Zn2+, given that there is no commercial Ion Selective Electrode. In this work, both techniques have been applied to synthetic samples (containing Zn and NTA) and natural samples (Rhine river water and soils), showing good agreement. pH fluctuations in DMT and N2/CO2 purging system used in AGNES did not affect considerably the measurements done in Rhine river water and soil samples. Results of DMT in situ of Rhine river water are comparable to those of AGNES in the lab. The comparison of this work provides a cross-validation for both techniques.
Strategies in the application of the Donnan membrane technique.
Weng, L.P. ; Vega, F.A. ; Riemsdijk, W.H. van - \ 2011
Environmental Chemistry 8 (2011)5. - ISSN 1448-2517 - p. 466 - 474.
metal-ion concentrations - soil solution - chemical speciation - organic-matter - heavy-metals - sandy soil - dynamic speciation - humic substances - model parameters - trace-metals
e Donnan membrane technique (DMT) can be applied to measure free ion concentrations both in laboratory and in situ in the field. In designing DMT experiments, different strategies can be taken, depending on whether accumulation is needed. (1) When the free ion concentration is above the detection limit of the analytical technique (e.g. ICP-MS), no accumulation is needed and no ligand is added to the acceptor. Measurement can be based on the Donnan membrane equilibrium. (2) When an accumulation of less than 500 times is needed, an appropriate amount of ligand can be added to the acceptor and measurement can be based on the Donnan membrane equilibrium. (3) When an accumulation factor of larger than 500 times is needed, a relatively large amount of ligand is added to the acceptor and measurement can be based on the transport kinetics. In this paper, several issues in designing the DMT experiments are discussed: choice of DMT cell, measurement strategies and ligands and possible implication of slow dissociation of metal complexes in the sample solution (lability issue). The objective of this paper is to give better guidance in the application of DMT for measuring free ion concentrations in both synthetic and natural samples.
Evaluation of models for metal partitioning and speciation in soils and their use in risk assessment
Groenenberg, J.E. - \ 2011
Wageningen University. Promotor(en): Rob Comans; Wim de Vries. - [S.l. : S.n. - ISBN 9789085858485 - 218
toxicologie - metalen - bodemchemie - risicoschatting - transportprocessen - geochemie - bodemoplossing - organisch bodemmateriaal - modellen - toxicology - metals - soil chemistry - risk assessment - transport processes - geochemistry - soil solution - soil organic matter - models
In this thesis models were developed and evaluated which describe metal partitioning and speciation in soils. Both partition-relations and multisurface models were developed and evaluated on their performance for a large set of elements
Effects of Lability of Metal Complex on Free Ion Measurement Using DMT
Weng, L.P. ; Riemsdijk, W.H. van; Temminghoff, E.J.M. - \ 2010
Environmental Science and Technology 44 (2010)7. - ISSN 0013-936X - p. 2529 - 2534.
donnan membrane technique - soil solution - in-situ - dynamic speciation - trace-metals - copper - waters - dissociation - equilibrium - dialysis
Very low concentrations of free metal ion in natural samples can be measured using the Donnan membrane technique (DMT) based on ion transport kinetics. In this paper, the possible effects of slow dissociation of metal complexes on the interpretation of kinetic DMT are investigated both theoretically and experimentally. The expressions of the lability parameter, , were derived for DMT. Analysis of new experimental studies using synthetic solution containing NTA as the ligand and Cu2+ ions shows that when the ionic strength is low (=0.2 mM Ca(NO3)2) the dissociation rate of NTACu becomes the limiting step in Cu transport of the DMT measurement. In natural waters, dissolved organic matter (DOM) is the most important source of ligands that complex metals. By comparing the fraction of labile species measured using other dynamic sensors (DGT, GIME) in several freshwaters, it is concluded that in most waters ion transport in DMT is controlled by diffusion in the membrane. Only in very soft waters (
Donnan Membrane Technique (DMT) for Anion Measurement
Alonso Vega, M.F. ; Weng, L.P. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2010
Analytical Chemistry 82 (2010)7. - ISSN 0003-2700 - p. 2932 - 2939.
dissolved organic-matter - metal-ion concentrations - soil solution - chemical speciation - heavy-metals - sandy soil - colloidal particles - aqueous-solutions - water extracts - activity model
Donnan membrane technique (DMT) is developed and tested for determination of free anion concentrations. Time needed to reach the Donnan membrane equilibrium depends on type of ions and the background. The Donnan membrane equilibrium is reached in 1 day for Cl-, 1-2 days for NO3-, 1-4 days for SO42- and SeO42-, and 1-14 days for H2PO4- in a background of 2-200 mM KCl or K2SO4. The strongest effect of ionic strength on equilibrium time is found for H2PO4-, followed by SO42- and SeO42-, and then by Cl- and NO3-. The negatively charged organic particles of fulvic and humic acids do not pass the membrane. Two approaches for the measurement of different anion species of the same element, such as SeO42- and HSeO3-, using DMT are proposed and tested. These two approaches are based on transport kinetics or response to ionic strength difference. A transport model that was developed previously for cation DMT is applied in this work to analyze the rate-limiting step in the anion DMT. In the absence of mobile/labile complexes, transport tends to be controlled by diffusion in solution at a low ionic strength, whereas at a higher ionic strength, diffusion in the membrane starts to control the transport
Evaluation of approaches to calculate critical metal loads for forest soils
Vries, W. de; Groenenberg, J.E. - \ 2009
Environmental Pollution 157 (2009)12. - ISSN 0269-7491 - p. 3422 - 3432.
biotic ligand model - scots pine-seedlings - organic-matter - humic substances - soil solution - kola-peninsula - surface waters - acute toxicity - air-pollution - fresh-waters
This paper evaluates approaches to calculate acceptable loads for metal deposition to forest ecosystems, distinguishing between critical loads, stand-still loads and target loads. We also evaluated the influence of including the biochemical metal cycle on the calculated loads. Differences are illustrated by examples of Cd, Cu, Pb and Zn for a deciduous forest on five major soil types in the Netherlands. Stand-still loads are generally lower than critical loads, which in turn are lower than the target loads indicating that present levels are below critical levels. Uncertainties in the calculated critical loads are mainly determined by the uncertainty in the critical limits and the chemical speciation model. Including the metal cycle has a small effect on the calculated critical loads. Results are discussed in view of the applicability of the critical load concept for metals in future protocols on the reduction in metal emissions.
Measuring free metal ion concentrations in multicomponent solutions using Donnan Membrane Technique
Kalis, E.J.J. ; Temminghoff, E.J.M. ; Weng, L.P. ; Riemsdijk, W.H. van - \ 2007
Analytical Chemistry 79 (2007)4. - ISSN 0003-2700 - p. 1555 - 1563.
natural organic-matter - speciation measurements - selective electrode - soil solution - trace-metals - nica-donnan - in-situ - binding - waters - model
Among speciation techniques that are able to measure free metal ion concentrations, the Donnan membrane technique (DMT) has the advantage that it can measure many different free metal ion concentrations simultaneously in a multicomponent sample. Even though the DMT has been applied to several systems, like surface waters, soil solutions, and manure slurry, basic features and calibrations with model calculations of the laboratory and field DMT have not been done sufficiently yet. Therefore, we tested the application of the DMT on metal complexation with several synthetic and natural ligands and the applicability of the dynamic mode of the DMT. The results show that there is a high agreement between the calculated and measured free metal ion concentrations in solutions containing synthetic (nitriloacetic acid, diglycolic acid) and natural organic ligands (fulvic acid, humic acid) at various pH values. Both the laboratory DMT and the field DMT give very similar results. In a solution containing labile ligands, equilibrium time is smaller than in a donor solution containing inert ligands or no ligands. Moreover, when labile ligands are present in the donor solution, a dynamic procedure can be used to decrease equilibrium time. This procedure cannot be applied when no ligands or only inert ligands are present.
Chemical speciation and bioavailability of heavy metals in soil and surface water
Kalis, E.J.J. - \ 2006
Wageningen University. Promotor(en): Willem van Riemsdijk, co-promotor(en): Erwin Temminghoff. - [S.l.] : S.n. - ISBN 9789085045250 - 142
zware metalen - bodem - oppervlaktewater - chemische speciatie - biologische beschikbaarheid - humuszuren - technieken - lolium perenne - bodemoplossing - bodemverontreiniging - heavy metals - soil - surface water - chemical speciation - bioavailability - humic acids - techniques - lolium perenne - soil solution - soil pollution
Keywords:Metal speciation, Bioavailability, Lolium perenne , Free metal ion, Donnan Membrane Technique, Humic acid, Metal uptake, Speciation techniques, Competition, Soil (solution)
The total metal content of the soil or total metal concentration in the soil solution or surface waters is not a good indicator for metal availability to organisms. Instead, the free ion activity model (FIAM) states that the free metal ion concentration is the determining factor in heavy-metal uptake. Even though several exceptions have been found to the FIAM,the free metal ion is often responsible for binding at an organism's surface. Competition between metal ions at this biotic surface is accounted for by the Biotic Ligand Model (BLM), which is an extension of the FIAM.
One of the techniques that can be used to measure many different free metal ion concentrations simultaneously in a multicomponent sample is the Donnan Membrane Technique (DMT).With the DMT, the free metal ions equilibrate over a hydrophilic cation-exchange membrane between a sample compartment and an acceptor compartment, in which the free metal ion concentration is measured. The laboratory tests on the DMT showed that there is a high agreement between the calculated and observed free metal ion concentrations in solutions containing synthetic and natural ligands at various pH values. A new field DMT cell was developed to measure free metal ion concentrations in situ in surface waters. Because free metal ion concentrations in surface waters are commonly below the detection limit of theinductively coupled plasma - mass spectrometer(ICP-MS), the detection limit of the DMT was decreased by making use of a ligand in the DMT. The field DMT measured free metal ion concentrations in situ in the River Rhine in the Netherlands, the Furtbach Stream and Lake Greifen in Switzerland and in the River Wyre in the UK. The measured fractions of free metal ions ranged from 0.015 - 0.63 % for Cu to 4.3 - 13 % for Zn. The variability of the free metal fractions has a large influence on metal uptake and metal transport. The field DMT could detect small fluctuations in the free metal ion concentration due to changing water temperatures.
Uptake studies with Lolium perenne in nutrient solutions showed that the metal content in the shoots of the plants depends on the metal content in the roots and that the metal content in the roots is linearly related to the adsorption of metals on the root surface. In a multicomponent system at metal concentrations of 1 μM, humic acid decreased Cu, Pb, and Fe adsorption at the root surface, but humic acid increased Cd, Zn, and Mn adsorption at the root surface. Apparently, complexation of cations with high affinity for (dissolved) organic matter may lead to increased uptake of cations with low affinity for organic matter because of competition between cations at the root surface. These plantstudies show that a ligand is able to do both, decrease and increase the bioavailability of heavy metals.
In a pot experiment using ten different contaminated soils it was found that the metal adsorption at the root surface of Lolium perenne is pH dependently related to the free, labile or total metal concentration in CaCl 2 extractions of these soils. Free metal ion concentrations in the CaCl 2 extractions were measured by DMT, whereas Diffusive Gradients in Thin-films (DGT) and Scanning Chronopotentiometry (SCP) were used to measure the sum of free and labile metal fractions.Because of the pH dependent metal binding at the root surface, the pH of the soil has to be taken into account when CaCl 2 extractions are used as a basis for risk assessment towards plants.The rate-limiting steps in the metal transport from soil to plant, which can be controlled by metal diffusion in solution or metal uptake by the plant, can be determined by comparing the total, labile and free metal fractions.
Organic anion exudation by ectomycorrhizal fungi and Pinus sylvestris in response to nutrient deficiences
Schöll, L. van; Hoffland, E. ; Breemen, N. van - \ 2006
New Phytologist 170 (2006)1. - ISSN 0028-646X - p. 153 - 163.
in-vitro - paxillus-involutus - soil solution - forest soil - mg2+ deficiency - oxalic-acid - oxalate - roots - mycorrhizal - seedlings
Low molecular weight organic anions (LMWOA) can enhance weathering of mineral grains. We tested the hypothesis that ectomycorrhizal (EcM) fungi and tree seedlings increase their exudation of LMWOA when supply of magnesium, potassium and phosphorus is low to enhance the mobilization of Mg, K and P from mineral grains. ¿ Ectomycorrhizal fungi and Pinus sylvestris seedlings were cultured in symbiosis and in isolation on glass beads with nutrient solution or with sand as a rooting medium, with a complete nutrient supply or with Mg, K, P or N in low supply. Concentrations of all dicarboxylic LMWOA in the rooting medium were measured. ¿ Nonmycorrhizal seedlings released predominantly malonate. Colonization with Hebeloma longicaudum decreased the amount of organic anions exuded, whereas Paxillus involutus and Piloderma croceum increased the concentration of oxalate but not the total amount of LMWOA. Phosphorus deficiency increased the concentration of LMWOA by nonmycorrhizal and EcM seedlings. Magnesium deficiency increased the concentration of oxalate by nonmycorrhizal and EcM seedlings, but not the concentration of total LMWOA. Paxillus involutus grown in pure culture responded differently to low nutrient supply compared with symbiotic growth. ¿ Ectomycorrhizal fungi did not increase the total concentration of LMWOA compared with nonmycorrhizal seedlings but, depending on the fungal species, they affected the type of LMWOA found.
Kinetic aspects of Donnan membrane technique for measuring free trace cation concentration
Weng, L.P. ; Riemsdijk, W.H. van; Temminghoff, E.J.M. - \ 2005
Analytical Chemistry 77 (2005)9. - ISSN 0003-2700 - p. 2852 - 2861.
metal speciation - soil solution - stripping chronopotentiometry - copper - dialysis - cadmium
Addition of ion complexation ligands in the acceptor solution in the Donnan membrane technique (DMT) can lower its detection limit for free metal ion concentration in natural samples. In this paper, the influence of added ligands on the transport behavior of trace ions in DMT was studied using numerical and analytical models and experimental tests. The results show that addition of ligands in the acceptor can significantly influence the time to reach the Donnan membrane equilibrium. Depending on several factors, the flux can be controlled by the diffusion in the stagnant solution film at the solution-membrane interface, by the diffusion in the membrane, or by both. The conditions under which the diffusion in the solution film or in the membrane becomes the rate-limiting step are discussed and approximate analytical solutions for some special cases are presented. Very low concentrations of free metal ion can be measured using the ligand complexation DMT. Depending on the degree of complexation in the sample, the measurement can be based on either the Donnan membrane equilibrium (when the complexation degree is low) or the kinetic interpretation of the ion transport (when the complexation degree is high).
Calculation of critical loads for cadmium, lead and mercury; background document to a mapping manual on critical loads of cadmium, lead and mercury
Vries, W. de; Schütze, G. ; Lofts, S. ; Tipping, E. ; Meili, M. ; Römkens, P.F.A.M. ; Groenenberg, J.E. - \ 2005
Wageningen : Alterra (Alterra-report 1104) - 143
cadmium - lood - kwik - zware metalen - uitspoelen - ecosystemen - methodologie - oppervlaktewater - bodemoplossing - terrestrische ecosystemen - aquatische ecosystemen - ecotoxicologie - cadmium - lead - mercury - heavy metals - leaching - ecosystems - methodology - surface water - soil solution - terrestrial ecosystems - aquatic ecosystems - ecotoxicology
This report on heavy metals provides up-to-date methodologies to derive critical loads for the heavy metals cadmium (Cd), lead (Pb) and mercury (Hg) for both terrestrial and aquatic ecosystems. It presents background information to a Manual on Critical Loads for those metals. Focus is given to the methodologies and critical limits that have to be used to derive critical loads can be derived for Cd, Pb and Hg in view of : (i) ecotoxicological effects for either terrestrial or aquatic ecosystems.and (ii) human health effects for either terrestrial or aquatic ecosystems. For Hg, a separate approach is described to estimate critical levels in precipitation in view of human health effects due to the consumption of fish. The limitations and uncertainties of the approach are discussed including: (i) the uncertainties and particularities of the steady-state models used and (ii) the reliability of the approaches that are applied to derive critical limits for critical total dissolved metal concentrations in soil solution and surface water
Characterization, desorption, and mining of phosphorus in noncalcareous sandy soils
Koopmans, G.F. - \ 2004
Wageningen University. Promotor(en): Oene Oenema; Willem van Riemsdijk, co-promotor(en): Wim Chardon. - Wageningen : Alterra - ISBN 9789032703318 - 168
fosfor - eutrofiëring - oppervlaktewater - zandgronden - uitspoelen - bodemoplossing - biologische beschikbaarheid - phosphorus - eutrophication - surface water - sandy soils - leaching - soil solution - bioavailability
In areas with intensive livestock farming, soils have been enriched with phosphorus (P), following heavy applications of animal manure. These soils are a risk for nearby surface waters, as the leaching of P from these soils contributes to eutrophication of these surface waters. This study was set up to better understand the speciation and desorption of P in noncalcareous sandy soils, so as to contribute to the development of management guidelines for these soils.
Aluminium speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan
Weng, L.P. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2002
Water Research 36 (2002)17. - ISSN 0043-1354 - p. 4215 - 4226.
metaalionen - aluminium - modellen - bodemoplossing - membranen - chemische speciatie - adsorptie - grondanalyse - bodemwater - metal ions - aluminium - models - soil solution - membranes - chemical speciation - adsorption - soil analysis - soil water - dissolved organic-matter - contaminated sandy soil - metal-ion binding - humic substances - ph - complexation - copper - solubility - protons - field
The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10¿9 M and the equilibration takes 3¿4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3¿7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods
Interactions between metal ions and biogeo-surfaces in soil and water : basis for quantitative risk assessment
Weng, L.P. - \ 2002
Wageningen University. Promotor(en): W.H. van Riemsdijk; E.J.M. Temminghoff. - S.l. : S.n. - ISBN 9789058086075 - 193
metaalionen - zware metalen - risicoschatting - oppervlakten - bodem - bodemoplossing - water - chemische speciatie - adsorptie - bodemwater - milieu - metal ions - heavy metals - risk assessment - surfaces - soil - soil solution - water - chemical speciation - adsorption - soil water - environment
To provide the basis for an improved quantitative risk assessment of heavy metals in the environment, the interactions between the metal ions and the biogeo-surfaces in soil and water were studied using both experimental and modelling approaches.
The Donnan membrane technique was developed and optimised for the measurement of metal speciation in soil solutions, in which a soil column was linked to the Donnan cell to provide buffering capacities. In acid natural waters and soils, aluminium is potentially a relatively strong competitor for the heavy metals to the binding on colloidal particles such as organic matter. Using the Donnan membrane technique, aluminium binding to purified humic acid and to the dissolved organic matter in soil solutions was measured. The ability of the NICA-Donnan model for the prediction of Al binding to humic substances was tested.
A multi-surface model was developed for the prediction of metal speciation in soil and water. This model can also be used to estimate the relative contribution of the individual sorbents to the control of metal distribution. This multi-surface model considers soil as a set of independent sorption surfaces. Metal binding to soil organic matter (solid and dissolved), to clay mineral and to iron hydroxides was modelled using the NICA-Donnan, Donnan, DDL and CD-MUSIC models. This model approach was validated against the concentrations of total dissolved metal concentration and the activities of free metals in sandy soil samples measured using the Donnan membrane technique.
The interactions between the metal ions and the natural organic matter are not only important for the metal distribution, but also for the solubility and mobility of organic matters. Using the NICA-Donnan model, the effects of the binding of protons and metal ions on the physico-chemical behaviour of humic acid was studied. It was found that the coagulation of humic acid started when the calculated electrostatic potential was less negative. The electrostatic potential of the dissolved organic matter in the soil solution of six forest soil profiles was calculated using the same model. The measured concentration of the dissolved organic matter also decreased in a soil profile, as the calculated potential became less negative. Humic and fulvic acids are the major components in the dissolved organic matter. The mobility and transport of humic and fulvic acids were studied in a column experiment. By comparing the breakthrough curves and the modelled physico-chemical behaviour, it was found that coagulation might be important in the control of the solubility and mobility of humic acid, while adsorption was more likely the mechanism that could explain the immobilisation of fulvic acid in this soil.
The experimental and the modelling approaches developed are helpful in improving the quantitative risk assessment of the heavy metals. Pot experiments using three different soils and a solution culture experiment have been conducted to study the effects of pH and soil characteristics on the phytotoxicity of nickel. Using the model predictions the differences in the bioavailability of Ni in the three different soils could be explained. By comparing the toxicity of the free Ni 2+ion in the nutrient solution and in the soil solution, the toxicity of Ni in the soils could be predicted reasonably using the quantitative approach.
The developedDonnan membrane technique is proved to be a useful analytical technique for the determination of metal speciation in soil and water samples. Further research is needed to improve the method to make it capable to measure lower concentrations. The multi-surface model approach proposed in this research is validated against the measurements of the samples from several different soils. Further validation and improvement of this model approach can be achieved after comparing the prediction with the measurement for more different soils, and by better understanding of the interactions between metal ions and the biogeo-surfaces.
Modelling Water Flow and Solute Transport for Horticultural and Environmental Management
Feddes, R.A. ; Dam, J.C. van - \ 2002
Acta Horticulturae 573 (2002). - ISSN 0567-7572 - p. 107 - 117.
grondwaterstroming - bodemwaterbeweging - simulatiemodellen - voedingsoplossingen - tuinbouw - agrarische bedrijfsvoering - milieubeheer - bodemoplossing - groei - bodemmorfologie - groundwater flow - soil water movement - simulation models - nutrient solutions - horticulture - farm management - environmental management - soil solution - growth - soil morphology
During the past 10 years, the simulation model SWAP (Soil, Water, Atmosphere, Plant) was developed by the Sub-Department Water Resources of Wageningen University jointly with the Department Water and Environment of Alterra Green World Research. SWAP simulates vertical transport of water, solutes and heat in variably saturated, cultivated soils at field scale level and during whole growing seasons. Different versions of the model have been applied worldwide in research, education and as a decision support tool in the management of agricultural, horticultural and natural systems water flow in homogeneous and heterogeneous soils with or without the influence of groundwater. The main features of and theoretical concepts behind SWAP are described, in particular soil water flow, solute transport and crop growth.
The influence of water percolation on flow of light non aqueous phase liquids in soil
Marsman, A. - \ 2002
Wageningen University. Promotor(en): S.E.A.T.M. van der Zee. - S.l. : S.n. - ISBN 9789058087348 - 141
waterstroming - horizontale stroming - modellen - percolatie - bodemoplossing - permeabiliteit - bodemwater - technieken - water flow - horizontal flow - models - percolation - soil solution - permeability - soil water - techniques
Keywords,: multi-phase flow, entrapment, numerical modeling, similarity solution, horizontal migration, percolation theory, relative permeability.
In this thesis the physical behavior of Light Non-Aqueous Phase Liquids (LNAPL) at the capillary fringe, is studied with multiphase flow models. Phenomena like a fluctuating water table or percolation of (infiltration) water have a large impact on this behavior. Both the geometry and the mobility of the LNAPL lens are affected. These two physical phenomena mentioned imply downwards and upwards water flow through the LNAPL lens. Different techniques were used in this investigation. Numerical calculations show that fluctuations of the phreatic groundwater level result in retardation of the horizontal migration of the LNAPL lens over the groundwater level. An expression is derived which quantifies the part of the simulated time during which the LNAPL can actually flow. This expression is implemented in an existing analytical solution that describes horizontal LNAPL migration, to enable that the effect of a fluctuating water level can be calculated analytically. Laboratory experiments are performed which verify these results. The effect of water flow through an LNAPL lens also affects the mobility of LNAPL. Numerical results show that both for upwards and for downwards water invasion of a lens, the mobility of the LNAPL has increased significantly. To obtain more qualitative insight on the pore scale, percolation theory is used. Percolation theory is applied to this problem and the appropriate series of drainage and imbibition processes are calculated to simulate the water percolation. The accompanying relative permeabilities show that the mobility increases after water percolation. Qualitative insight on the pore scale shows that the LNAPL is displaced to a larger amount of pore radii which advances the mobility of the LNAPL. This observation is in agreement with the numerical results.
Chemical composition of the humus layer, mineral soil and soil solution of 150 forest stands in the Netherlands in 1990
Vries, W. de; Leeters, E.E.J.M. - \ 2001
Wageningen : Alterra (Alterra-rapport 424.1) - 113
bosgronden - humus - bodemoplossing - bodemchemie - bossen - eutrofiëring - zure depositie - zware metalen - verzuring - nederland - bodemverzuring - bosvitaliteit - milieu - forest soils - humus - soil solution - soil chemistry - forests - eutrophication - acid deposition - heavy metals - acidification - netherlands - monitoring
A nationwide assessment of the chemical composition of the humus layer, mineral topsoil (0-30 cm) and soil solution in both topsoil and subsoil (60-100 cm) was made for 150 forest stands in the year 1990. The stands, which were part of the national forest inventory on vitality, included seven tree species and were all located on non-calcareous sandy soils. Results show increased levels of nitrogen, aluminium, lead and cadmium in at least one of the various soil compartments, indicating the occurrenceof eutrophication, acidification and heavy-metal pollution. Tree species and stand characteristics, such as tree height and canopy coverage, appear to have the largest effect on the concentration level of the various chemical parameters by influencing the input by atmospheric deposition. The various assessments allowed the calculation of various parameters related to aluminium dissolution, cation exchange and phosphate adsorption, to be used in simulation models.
Chemical composition of the humus layer, mineral soil and soil solution of 200 forest stands in the Netherlands in 1995
Leeters, E.E.J.M. ; Vries, W. de - \ 2001
Wageningen : Alterra (Alterra-rapport 424.2) - 108
bosgronden - humus - bodemoplossing - bodemchemie - bossen - eutrofiëring - zure depositie - zware metalen - verzuring - nederland - bodemverzuring - bosvitaliteit - milieu - forest soils - humus - soil solution - soil chemistry - forests - eutrophication - acid deposition - heavy metals - acidification - netherlands - monitoring
A nationwide assessment of the chemical composition of the soil solid phase and the soil solution in the humus layer and two mineral layers (0-10 cm and 10-30 cm) was made for 200 forest stands in the year 1995. The stands were part of the national forest inventory on vitality, included seven tree species and were all located on non-calcareous sandy soils. The soils are nearly all characterized by high nitrogen and metal contents in the humus layer ans low pH and base saturation values in the minerallayer, indicating the occurrence of eutrophication, acidification and heavy metal pollution. Of those stands, 124 were also sampled and analysed in 1990. Compared with 1990, results for the humus layer show a decrease (release) in nitrogen and metal contents and pools, and a decrease in total and exchangeable pools of base cations, combined with increase in hydrogen saturation. This indicates a decrease in eutrophication but an ongoing acidification. The soil solution, however, shows a decrease in Al/Caand NH4/K ratios, implying a slight recovery from acidification. For the mineral soil, the changes in element pools are too unreliable to draw any distinct conclusion.
Release rates of Al from inorganic and organic compounds in a sandy podzol, during laboratory experiments
Salm, C. van der; Westerveld, J.W. ; Verstraten, J.M. - \ 2000
Geoderma 96 (2000)3. - ISSN 0016-7061 - p. 173 - 198.
bodemoplossing - bodem - aluminium - zure gronden - adsorptie - soil solution - soil - aluminium - acid soils - adsorption
Research with respect to release rates of Al and Al concentrations in the soil solution has led to two contrasting hypotheses, stressing either the importance of kinetically constrained dissolution reactions or the role of complexation of Al to soil organic matter. The existence of two contrasting hypotheses is partly due to the fact that the interpretation of existing results is hampered by the lack of specificity of the extractants used to quantify the organic and inorganic pools of Al and by the fact that simultaneous measurements on the release of Al and the change in Al pools are missing. This study was conducted to obtain more information on the release rates of Al from various amorphous pools and to evaluate the validity of the above hypotheses. To overcome the above-mentioned shortcomings both release rates of Al and changes in the various,Al pools were measured during the experiment. Experiments were conducted for Ap, Bs and C horizons from a sandy podzol. Results indicated that Al was released from both the inorganic Al pool (oxalate minus pyrophosphate extractable Al) and the strongly bound organic Al pool (pyrophosphate minus CuCl2 extractable Al) according to a first-order reaction. The decline in the weakly bound organic Al pool (CuCl2 extractable minus adsorbed Al) could be described by a rapid dissolution of part of the pool, combined with an equilibrium reaction describing the complexation of Al to organic sites. Rate constants were highest for the non-complexed part of the weakly bound organic Al pool, intermediate for the inorganic Al pool and lowest for the strongly bound organic Al pool. Large differences exist in rate constants of the organic pools between the three horizons. Differences between the rate constants of the inorganic Al pool for the three horizons were not significant.