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Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem-van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17¿

On the Loess Plateau in China, soil erosion amounts to between 10 000 and 25 000 tons/km2/year. In 1998, the EROCHINA project was started, with the major objective of developing alternative land-use and soil and water conservation strategies for the Loess Plateau, using the LISEM soil erosion model. In order to provide the model with accurate input on soil hydraulic properties of the catchment, this study tried to quantify these properties for major land-use units and to examine the effects of the statistically identified in-field heterogeneity on model outcome. The study area (Danangou catchment) is located in the middle part of the Loess Plateau in the northern part of Shaanxi Province. The catchment is about 3.5 km2 in size. To determine the hydraulic properties of the soil, a sampling scheme was implemented to measure unsaturated conductivity and water retention characteristics. The saturated conductivity measurements were performed on land-use clusters, based on treatment and plant and soil differences. A 100×100 m sampling grid was set out on 12 fields, with 1×1 m grid squares. On each field, 10 sampling spots were randomly selected, using Simple Random Sampling. The sensitivity of the LISEM model to the measured heterogeneity of saturated conductivity was analysed by using the geometric mean and standard deviation (S.D.) of the Ks-optimized of the various land-use units to calculate discharge and soil loss during a single rain event. This proved that, using the standard deviation of the saturated conductivity, which was 30–50%, the calculated discharge and total sediment losses varied by a factor 2. Using the standard deviation had a minor effect on the calculated sediment concentration. As regards the on-site effects, the use of the geometric mean of Ks minus the S.D. resulted in an increase in the level of erosion, while the use of geometric mean of Ks plus the S.D. value resulted in a significant decrease in erosion level relative to that obtained using the geometric mean of Ks itself. Using randomly selected sampling spots and a calibration procedure as was done in the present study make detailed information on Ks available, which can be used to compare alternative land-use options for their effectiveness in reducing discharge and sediment losses.

Numerical modelling of the transient moisture fluxes helps in the development of appropriate water management practices, but requires site-specific information on soil hydraulic properties. Forward simulations with a given set of Van Genuchten (VG) model parameters indicate that different soils act differently in their temporal variable evapotranspiration (ET) response under deep-water table/free drainage conditions. Since actual ET fluxes can be recovered from remote sensing measurements, a new possibility is established to derive soil hydraulic functions under actual field conditions for a range of spatial scales. Thus, inverse modelling of ETa fluxes is a promising way to estimate the so-called effective soil hydraulic functions. We numerically explore the possibility of inverse ET modelling to derive VG model parameters for semi-arid regions. The utility of this technique is evaluated using a simulation model to create a ‘no error data set’ of ET fluxes for cotton crop. Objective functions using actual ET and actual transpiration (T) are defined. Backward simulations are carried out to re-assess selected VG model parameters for the three-soil types, i.e. sand, loamy sand and sandy clay loam. A realistic ET data set is created from the no error data set by incorporating different levels of random error. Seasonal simulated water balance components (ET, deep percolation and change in profile storage) are compared to study the hydrological performance of the inversely estimated soil hydraulic functions. Results indicate that the moisture stress period under fully developed crops is most appropriate for sampling ET fluxes to solve the proposed inverse problem. It is also observed that frequent observations of ET fluxes are desired to reduce undesirable correlation between different fitting parameters. It is observed that when ET fluxes are very accurate, the VG model parameters α, n and θs (θr, ks and λ fixed at actual values) are optimised precisely with 12 ET data points. Inverse fitting of these parameters (α, n and θs) utilising perturbed data on ET fluxes results in effective soil hydraulic functions, which reliably predict different water balance components for sand and loamy sand soils.

Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem-van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17

A small number of measuring points may inflict a bias on the characterisation of flow and transport based on field experiments in the unsaturated zone. Simulation of pure advective transport of a Gaussian plume through a setup of 30 regularly placed measuring points revealed regular temporal fluctuations about the real spatial moments. An irregular setup predicted both irregular fluctuations and larger discrepancies from the real value. From these considerations, a regular setup is recommended. Spatial moments were sensitive to the plume size relative to the distance between individual measuring points. To reduce prediction errors of the variance, the distance between the measuring points should be less than twice the standard deviation of the examined plume. The total size of the setup should cover several standard deviations of the plume to avoid mass being lost from the monitored area. Numerical simulations of a dispersing plume (comparing calculations based on 9000 nodes with 30 measuring points) revealed that vertical and horizontal centres of mass were predicted well at all degrees of heterogeneity, and the same was the case for horizontal variances. Vertical variances were more susceptible to prediction errors, but estimates were of the same order of magnitude as the real values.

The hydrological problem to correctly partition rainfall at various scales may require scale dependent models. This study introduces a new method to identify scale dependent state space models in a hydrological context. In addition it investigates relations between model structure, resolution and uncertainty for the case of overland flow from a hillslope. The main strengths of the method are the ability to evaluate a very large set of candidate models, general applicability, the possibility to interpret identified models in a physical sense, and computational simplicity. Weaknesses are the possibly complex models that result, computation time required, and the relative poor fit of models as compared to methods with more strict assumptions on errors. For these reasons the method is mainly suitable as a first stage in an identification procedure, leading to the selection of a limited number of candidate models. For the case of overland flow at the hillslope scale it was found that model structure, resolution and uncertainty are closely related. When compared to the total set of calibrated models the fittest (best) models are characterised by a small average parameter uncertainty and a constant number of parameters. However, marked structural model differences exist for equally fit models at different spatial and temporal resolutions. Considering the whole spectrum of spatial and temporal resolutions covered by calibrated models, the fittest models are found in a narrow range.

Many environmental and agricultural problems are not restricted to national boundaries and therefore require international cooperation if solutions are to be found. Often, these solutions require the ability to use soil data as input in simulation models, however, despite a number of recognised international standards, soil data are rarely compatible across national frontiers. This problem was encountered when creating the HY draulic PR operties of E uropean S oils (HYPRES) database. The data, which includes particle-size distributions, were collected from 20 institutions in 12 countries. Only a few of these institutions adhered strictly to a recognised international system. Therefore, interpolation of the cumulative particle-size distribution was required to achieve compatibility of particle-size distributions within the HYPRES database. In this study, four different interpolation procedures were evaluated. The accuracy of the different procedures was found to vary with size intervals between measured points of the particle-size distribution. The loglinear interpolation of the cumulative particle-size distribution has previously been used in various studies but was found to give the least accurate estimation of the four procedures. Fitting the Gompertz curve, which is a special asymmetric type of curve described by a closed-form equation, showed less sensitivity to size intervals between measured points. However, interpolation within some of the particle-size distributions was not sufficiently accurate and this procedure could not be applied to particle-size distributions where the number of measured size fractions was less than the number of model parameters. Fitting a nonparametric spline function to the particle-size distributions showed a considerable increase in accuracy of the interpolation with decreasing size intervals between measured points. As a novel approach, the similarity procedure was introduced which does not use any mathematical interpolation functions. It uses an external source of soil information from which soils are selected with particle-size distributions that match the distribution of the soil under investigation. This similarity procedure was capable of giving the most accurate interpolations. Once an extensive external reference data set with well-quantified particle-size distributions is available, the similarity procedure becomes a very powerful tool for interpolations. Based on the number and distribution of measured points on the particle-size distributions, a general rule was formulated to decide whether to fit a spline function or use the novel similarity procedure to estimate missing values. Results of this study were used to classify all soils in the HYPRES database into the same soil texture classes used in the 1:1.000.000 scale Soil Geographical Database of Europe.

Dry water repellent soils are known to inhibit water infiltration, ultimately forcing water to flow via preferential paths through the vadose zone. To study water flow and transport in a water repellent sandy soil, a bromide tracer experiment had been carried out, which started in the fall after winter wheat had been sown. Despite the uniform tracer application, soil core sampling indicated that bromide concentrations varied largely from place to place. Wetter sites in the experimental field received more bromide, due to lateral transport through a thin top layer. Wetting fronts infiltrated deeper here, leading to perturbed wetting fronts in the experimental field. In contrast to what was expected, the wetting front perturbations did not grow to fingers. Numerical results indicate that this was attributed to the relatively high soil water contents during the experiment, which caused the soil to be wettable instead of water repellent. The water-entry capillary pressure of the secondary wetting branch exceeds the air-entry capillary pressure of the primary drainage branch in this case. In the opposite situation, with the water-entry capillary pressure of the secondary wetting branch beneath the air-entry capillary pressure of the primary drainage branch, perturbations would have grown to fingers. Such a situation occurs during infiltration in initially dry, water repellent soil. The results presented illustrate the effect of antecedent moisture conditions on the formation of stable and unstable wetting fronts, and its relation to the moment of tracer application.

A long-term (>10 months) leaching experiment was conducted with a large clay soil column and a rain simulator to study unsaturated transport of the nematicide aldicarb and the herbicide simazine in a cracked clay soil. Water retention and soil conductivity were derived from experimental outflow data and deterministic parameter estimation techniques. Under conventional application rates and realistic rain events, aldicarb's aerobic metabolites were found in very high concentrations, and did not meet the normal EC levels for water during the entire measuring period. A mass balance for aldicarb showed that 0.35% of the initial dose was leached. However, when the two isosteric metabolites aldicarb-sulfoxide and aldicarb-sulfone were included in the mass balance, this percentage increased dramatically to 19.7%. Simazine was found in relatively low concentrations of 0.05–0.6 μ g/l, and only 0.11% of the initial dose was leached over 280 days. The absence of a `breakthrough behaviour' (peak exposure) implies long term delivery (chronic exposure) of the compound from the soil. The predictive performances of the widely used pesticide leaching models VARLEACH, LEACHP, MACRO, PESTLA and SIMULAT, which differ in their basic concepts for calculating water and solute transport and pesticide behaviour, were compared. This ring test revealed that none of the models were able to describe both water percolation and pesticide leaching to a completely satisfying degree. Moreover, there is little agreement on maximum pesticide concentrations and the time period in which these occur. This conclusion seriously limits the possibilities of model application and conducting reliable risk assessments for pesticides which are applied on the studied, or similar type of clay soils.

Evaporation from a cutover raised bog in The Netherlands was modelled using a detailed, physically based evaporation model for heterogeneous vegetation and unsaturated soil water how ''SWAPS''. The model enables a quantification of the role of heterogeneity on evaporation. Micro-meteorological measurements above a vegetation of Molinia caerulea (purple moor grass) in the cutover raised bog ''Engbertsdijksvenen'' are used for calibration and validation of the model. In the present study, it is investigated how small scale heterogeneity affects the prediction of evaporation. Therefore, two hypothetical variants, which represent two possible types of small scale heterogeneity in peatlands, are evaluated: (1) peatland in which drainage has resulted in a vegetation cover of 50% purple moor grass and 50% birch, (2) peatland in which after rewetting the vegetation consists of 50% purple moor grass and 50% Sphagnum mosses. The results show that characteristics of the evaporation from purple moor grass in the two variants are dissimilar. The evaporation from purple moor grass, forming the lower components of a vegetation stand (variant I), can be accurately predicted via radiation based models. In case purple moor grass is the exposed part of the vegetation (variant 2), such models are not likely to predict the evaporation from purple moor grass correctly. An exposed, aerodynamically rough vegetation requires a model that accounts for the vapour pressure deficit as well. (C) 1997 Elsevier Science B.V.

The variation in soil texture, surface moisture or vertical soil moisture gradient in larger scale atmospheric models may lead to significant variations in simulated surface fluxes of water and heat. The parameterization of soil moisture fluxes at spatial scales compatible with the grid size of distributed hydrological models and mesoscale atmospheric models (∼ 100 km2) faces principal problems which relate to the underlying microscopic or field scale heterogeneity in soil characteristics. The most widely used parameterization in soil hydrology, the Darcy-Richards (DR) equation, is gaining increasing importance in mesoscale and climate modelling. This is mainly due to the need to introduce plant-interactive soil water depletion and stomatal conductance parameterizations and to improve the calculation of deep percolation and runoff. Covering a grid of several hundreds of square kilometres, the DR parameterization in soil-vegetation-atmosphere-transfer schemes (SVATs) is assumed to be scale-invariant. The parameters describing the non-linear, area-average soil hydraulic functions in this scale-invariant DR-equation should be treated as calibration-parameters, which do not necessarily have a physical meaning. The saturated hydraulic conductivity is one of the soil parameters to which the models show very high sensitivity. It is shown that saturated hydraulic conductivity can be scaled in both vertical and horizontal directions for large flow domains. In this paper, a distinction is made between effective and aggregated soil parameters. Effective parameters are defined as area-average values or distributions over a domain with a single, distinct textural soil type. They can be obtained by scaling or inverse modelling. Aggregated soil parameters represent grid-domains with several textural soil types. In soil science dimensional methods have been developed to scale up soil hydraulic characteristics. With some specific assumptions, these techniques can be extrapolated from classical field-scale problems in soil heterogeneity to larger domains, compatible with the grid-size of large scale models. Particularly promising is the estimation of effective soil hydraulic parameters from area averaging measurements through inverse modelling of the unsaturated flow. Techniques to scale and aggregate the soil characteristics presented in this paper qualify for direct or indirect use in large scale meteorological models. One of the interesting results is the effective behaviour of the reference curve, which can be obtained from similar media scaling. If the conclusions of this paper survive further studies, a relatively simple method will become available to parameterize soil variability at large scales. The inverse technique is found to provide effective soil parameters which perform well in predicting both the area-average evaporation and the area-average soil moisture fluxes, such as subsurface runoff. This is not the case for aggregated soil parameters. Obtained from regression relationships between soil textural composition and hydraulic characteristics, these aggregated parameters predict evaporation fluxes well, but fail to predict water balance terms such as percolation and runoff. This is a serious drawback which could eventually hamper the improvement of the representation of the hydrological cycle in mesoscale atmospheric models and in GCMs.

A better understanding of leaching processes in raised beds is useful in assessing management options for acid sulphate soils. Field and laboratory studies were carried out to quantify the effects of soil physical properties and bypass flow on leaching processes of new, 1-year-old and 2-year-old raised beds for yam and pineapple cultivation in a Typic Sulfaquept in Tien Giang, Vietnam. The methylene blue staining technique was used to characterize the water-conducting pores in terms of number, stained area, and total pore perimeter at 10 cm depth intervals of six 1 × 1 m subplots. Undisturbed 20 cm X 25 cm soil cores taken from the raised beds were subjected to three 30 mm h −1 rains. Volume, aluminum and sulphate concentration of the outflows were monitored. Consolidation with time decreased the area and perimeter of water-conducting pores in 2-year-old pineapple beds to about a third, and bypass flow rate to about 80% of those in newly constructed beds. Consolidation did not affect macropore network geometry in yam beds because they were subjected to annual tillage and yam tubers were uprooted regularly. A13 + and SO 4 2− concentrations in the outflows of the newly constructed and 1-year-old raised beds were higher in pineapple, while those in 2-year raised beds were higher in yam.

In veel podzolgronden komt onder de humusinspoelingshorizont (BZh) plaatselijk een ijzerbandje (BZir) voor. De vorming daarvan hangt samen met een specifiek vochtfront dat optreedt als een slecht doorlatende bodemlaag op een goed doorlatende voorkomt. Op sommige kleine, relatief lage plekken, 'mini-vennetjes: is onder invloed van accumulatie van water en van veengroei het ijzerbandje verplaatst naar de diepere zandondergrond. Daardoor zijn hierin 'ijzerkuipen' gevormd. Van een aantal grotere vennen is bekend dat ze zijn gemarkeerd door verticale ijzerwanden. In dit artikel gaan we nader in op het ontstaan en de verbreiding van deze ijzerlaagjes en hun invloed op de waterbeweging in de grond

The impact of soil heterogeneity on the spatially average water budget of the unsaturated zone is investigated using a framework of analytical solutions. This framework was previously shown to adequately represent the long-term average water budget as well as its transient evolution. Nine combinations of three climate and three soil types are considered, covering a wide range of different conditions. In highly conductive soils, where evapotranspiration is limited by percolation through the lower boundary, heterogeneity increases the spatially average evapotranspiration relative to the uniform (scaled average) soil. In contrast, for less conductive soils the decreasing infiltration rates due to soil heterogeneity cause evapotranspiration to become smaller. Formally derived “equivalent” parameters, which are intended to capture the effect of soil heterogeneity by means of one set of soil hydraulic parameters, are shown to depend not only on the spatially heterogeneous parameters, but on climate as well. Moreover, the “equivalent” parameters derived for the long-term average water budgets are not valid for transient behavior.

In northern Burkina Faso (West Africa), a study was undertaken to explore the possibilities of restoring the infiltration capacity of crusted soils through the stimulation of termite activity. Treatments consisted of the application of a mulch of a mixture of wood and straw without insecticides (resulting in “termite plots”) and the application of the same mulch and an insecticide (Dursban with chloropyrifos as the active ingredient) to prevent termite activity (resulting in “non-termite plots”). Three rainfall simulations of 60 minutes duration with an intensity of 50 mm/h at an interval of 24 hours between the first and the second and 72 hours between the second and third simulation were applied, to study the effect of consecutive showers on termite-modified soil characteristics. Cumulative infiltration amounts, final infiltration rates, soil water content and porosity were larger and bulk density was smaller on termite plots as compared to non-termite plots. This suggests that termites may be an important agent in soil-crust control and in the improvement of soil physical properties in Sahelian ecosystems.

Soil maps are used to characterize spatial patterns of soil behaviour. A first approach is to characterize each soil map unit (SMU) by the behaviour of a pedogenetically representative profile; a second is to subsample each SMU and select from the sample a characteristic profile by its behaviour. The first approach was tested against the second. Using pedogenetically representative profiles resulted in biased estimations of functional properties related to water and solute transport. Soil profiles fitting to the definition of the SMU (impurities) corresponded to extreme values for four properties, which implies that impurities must be sampled when risk assessments must be made.

Grass-covered heavy basin clay soils in the Netherlands appeared to be water repellent. Water repellency in the top layers of these soils occurred mainly as a coating on the aggregates. The variation in soil moisture content over short distances was studied by sampling the soil 10 times during the period August 31, 1993, to December 22, 1994. Each time, 35 samples (100 cm3) were taken in close order over a distance of 195 cm at depths of 0–5, 10–15, 20–25, and 30–35 cm. Differences between minimum and maximum soil moisture contents were high in all layers sampled, occasionally as much as 28 vol %. When the clay soil is dry, a major proportion of the water from precipitation or sprinkler irrigation may flow rapidly through shrinkage cracks to the subsoil, bypassing the matrix of the clay peds. However, preferential flow is not limited to macropore flow: irregular wetting patterns are also formed through the small pores of the matrix. The relationship between dry bulk density and volumetric water content was found to be positive when the clay soil was relatively dry and negative when it was relatively wet.

The role of water-repellency in forming preferred flow paths and in accelerating solute transport is explained on the basis of extensive field measurements in a grass-covered water-repellent sandy soil in the Netherlands. When the 9 cm thick humous topsoil was wetted to 20-25 vol.%, preferred flow paths, or fingers, were formed in the sandy subosil. The fingers started at the layer interface at `weak' spots with a relatively low degree of potential water-repellency, and protruded vertically into the sandy subsoil. The fingers disappeared during dry periods and recurred at the same locations during new rain events.

Meststoffen en andere chemicaliën komen vaak sneller in het grondwater terecht dan modellen voorspellen. De meeste modellen zijn namelijk gebaseerd op de veronderstelling dat de bodem homogeen is, het water in de onverzadigde zone verticaal infiltreert en het vochtfront evenwijdig is aan het bodemoppervlak. In werkelijkheid stroomt het water vaak via preferente banen door de bodem. Preferente stroming heeft diverse oorzaken en kan in nagenoeg alle gronden optreden. In dit artikel wordt naar voren gebracht dat regenwater zich in zavel-, klei- en veengronden niet alleen snel naar de ondergrond verplaatst door scheuren en gangen, maar dat tevens de bovengrond ongelijkmatig bevochtigd wordt, waardoor vochtpatronen in de matrix van deze gronden ontstaan

Many sandy soils in the Netherlands have a water-repellent surface layer covering a wettable soil with a shallow groundwater table. Fingers form in the water-repellent surface layer and rapidly transport water and solutes to the wettable soil in which the streamlines diverge. Although several field observations are available, this system has not yet been studied systematically. In this paper, we present a model with a steady-state water flow to which solutes are added as a pulse. The model predicts the flow through the distribution zone and through the finger in the water-repellent surface layer with a closed form solution and transport in the wettable subsoil numerically. Model calculations show that the travel time through the water-repellent surface layer and the thickness and hydraulic conductivity of the wettable soil have the strongest effect on the arrival time of the solute pulse at groundwater level. The calculations also show that, assuming transport in the wettable subsoil to take place in fingers, the travel time is considerably shorter than when the diverging flow in the wettable soil is included.

Wetting front instability resulting in fingered flow has been found in both wettable and nonwettable soils. Understanding how and when this phenomenon occurs under field conditions is greatly limited. Laboratory research has resulted in a number of expressions for finger diameter. In this paper we test the applicability of one of these equations for three different soils in the Netherlands where detailed soil sampling of moisture content was done earlier. In addition, information needed for finger prediction, such as the main wetting and drying loops of the soil moisture characteristic curves and the unsaturated and saturated soil conductivities, were measured in the laboratory. Results show that predicted finger diameters for the two sandy soils agreed well with the observed moisture patterns, while for the loess soil the wetting front was flat as predicted. The finger diameters in dry soil were based on the main wetting loop and in the wet soils were dependent on the main drying loop.

Simulated estimates of crop yield were made for rainfed rice in a 50 ha dryland rice area. The aim was to investigate how soil units and management units of different sizes with different yields could be used to obtain values for areas of land. Two procedures were applied. First, yields were simulated at six sites, that were representative of six soil mapping units. Second, yields were simulated using soil information from 133 auger sites, and were interpolated over management units using block kriging. Differences between the two procedures for the total area and for a test set of 22 additionally sampled locations were small. A 60% increase in precision was achieved when relatively large management units were defined. A Geographical Information System was used to identify areas with greatest yield potential for rainfed dryland rice. Statistical analysis showed that the six soil units could be grouped into three yield classes. The largest yields were obtained for a sub-area comprising 11% of the survey area which was associated with a slowly permeable Bg horizon in the soil profile. It was concluded that the best procedure for the spatial interpolation of simulated rice yield should be based on preliminary simulation of crop yields. A sensitivity analysis of the impact of weather variability and soil heterogeneity on the variation of yield was useful to detect the importance of their contributions. The procedures developed in this study are of value in obtaining a reliable estimate of average yield, and can consequently be used for associated cost-benefit calculations.

Class pedotransfer functions were used to generate average hydraulic characteristics for distinct soil texture classes. Continuous pedotransfer functions were used to generate soil hydraulic characteristics from the actually measured median of the sand particle size, bulk density and percentages clay, silt and organic matter. Both approaches were used to predict the soil physical input data to calculate five different functional aspects of soil behaviour. The functional aspects were: number of workable days, number of days with adequate soil aeration, elapsed time until 10% breakthrough of chloride, amount of cadmium leached after one year and amount of Isoproturon leached after one year. Simulations of water and solute transport were made for 88 profiles which form a statistically representative set of profiles for cover sands in the northeastern part of the Netherlands. The calculated number of workable days did not depend on the type of pedotransfer used. However, the differences between the class and continuous pedotransfer function approach were significant for the other four functional aspects of soil behaviour. For adsorbing cadmium and adsorbing and degradable Isoproturon, differences between the two approaches were statistically significant because they were systematic. However, these differences were so small that they were irrelevant in practice. When to prefer which approach was ambiguous and depended on the functional aspect under consideration. When differences were not significant or irrelevant in practice, the cheaper and easier to use class pedotransfer function approach is preferred over the continuous pedotransfer function approach.

Water and solute input rates on the soil surface may vary considerably from place to place. Distribution flow, i.e., the process of water and solute flow in a lateral direction over and through the very first millimeter or centimeter of the soil profile, is an extremely important process in distributing the rainfall toward places where vertical transport occurs. This study was carried out to quantify the process the distribution flow and its underlying process mechanism. A KBr tracer was applied on two water repellent sandy soils to follow the actual flow paths of water and solutes in the upper part of the profile. On both experimental fields, distribution flow actually displaced the applied bromide laterally through a very thin layer on the top of the soil profile, referred to as the {open_quotes}distribution layer.{close_quotes} Distribution flow was directed to locations within the 0- to 2.5- cm layer, where the soil was the least water repellent. On these relatively wet areas, the highest concentrations of bromide could be found. There was an acceleration in the vertical transport of water and bromide on these sites. Effects of distribution flow on the local concentration of water and solutes can be expected to be evenmore » more pronounced in uneven terrains, where lateral displacements may increase from the millimeter-centimeter scale to tens of meters. Implications for modeling field-scale water and solute flow are outlined. 71 refs., 9 figs., 2 tabs.« less

The transport of a bromide tracer was studied in a heavy clay soil. After applying the tracer on day 0, water and bromide content profiles in the unsaturated zone were determined on days 6, 46, 209, 335, and 572. Furthermore, water samples were taken frequently from the groundwater and drain discharge and analyzed for bromide content. In the clay soil studied, solute transport occurred in three domains: large continuous macropores, smaller more tortuous mesopores, and the pores inside the soil aggregates. Bromide transport through the first domain, i.e., preferential flow through large macropores, amounted only to a few percent. This resulted, however, in maximum bromide concentrations in groundwater and drain discharge. Quantitatively, the most important solute transport occurred through the mesopores. This transport was characterized by high spatial variability, significant lateral transport, and low mobile water volumes (6%). At the field scale this resulted in the rapid leaching of solute in comparison with earlier experiments on sand and loam soils. After only 6 days and 34 mm net precipitation, the average bromide concentration peak had reached a depth of 55 cm. In spite of the heterogeneous transport and the presence of preferential flow, field-average solute concentration profiles exhibited regular and smooth shapes. Solute transport inside the soil aggregates played only an indirect role, i.e., via solute retardation as a result of convection and diffusion into the aggregates.

In soils with fingered flow, surface-applied solutes can reach the groundwater more rapidly than in the case of homogeneous wetting. This study was undertaken to demonstrate the occurrence of finger-like wetting patterns in a silt loam soil and a silty clay loam soil, and to investigate the influence of dry bulk density and water repellency on the observed soil moisture patterns. In both soils, dry bulk density was not a main factor in inducing wet finger-like patterns and high water content variability. Spatial variability of degree and persistence of potential water repellency and, accordingly, of soil water contents were high.

Many agricultural areas with humic-sandy and loamy-sandy soils are used also for the extraction of water for drinking-water supply. Model concepts have been developed for the fast preferential transport of plant protection products (pesticides) in such soils, e.g. by fingered and funneled flow. An inventory is given of experiments that may be suitable for the testing of preferential transport models for cultivated sandy soils (without macropores). The pesticide concentrations per depth in soil are highly variable, due to local differences in transport, adsorption and transformation. Measurements in both the subsoil and in the upper groundwater are scarce, also due to sampling problems. Suggestions are given to improve the characterisation of soil profiles and weather conditions. Sampling methods for soil and soil solution can easily miss the preferential transport pathways. The methods of pesticide analysis in soils samples are often not sensitive enough to measure concentrations relevant for groundwater quality. The present study serves as the starting point for selecting the most suitable data sets for model testing and for the design of more complete and detailed data sets in the future.

Many agricultural areas with humic-sandy and loamy-sandy soils are used also for the extraction of water for drinking-water supply. Model concepts have been developed for the fast preferential transport of plant protection products (pesticides) in such soils, e.g. by fingered and funneled flow. An inventory is given of experiments that may be suitable for the testing of preferential transport models for cultivated sandy soils (without macropores). The pesticide concentrations per depth in soil are highly variable, due to local differences in transport, adsorption and transformation. Measurements in both the subsoil and in the upper groundwater are scarce, also due to sampling problems. Suggestions are given to improve the characterisation of soil profiles and weather conditions. Sampling methods for soil and soil solution can easily miss the preferential transport pathways. The methods of pesticide analysis in soils samples are often not sensitive enough to measure concentrations relevant for groundwater quality. The present study serves as the starting point for selecting the most suitable data sets for model testing and for the design of more complete and detailed data sets in the future.

Unstable water flow in water-repellent unsaturated soils can significantly affect the processes of infiltration and soil water redistribution. A field experiment was carried out to study the effect of water-repellency on water and bromide movement in a coarse-textured soil in the southwestern part of The Netherlands. The field data were analyzed using a relatively simple numerical model based on the standard Richards' equation for unsaturated water flow and the Fickian-based convection-dispersion equation for solute transport. Water-repellency was accounted for by multiplying the water content and the unsaturated hydraulic conductivity of the soil with F, a factor equal to the volumetric fraction of soil occupied by preferential flow paths resulting from the unstable flow process. The good comparison of simulated and measured bromide concentrations suggests that the model provides a viable method for simulating unstable water flow in water-repellent soils.

The water status in plants is dependent on the xylem hydraulic conductance. In cut flowers, for example, the preservation of continuous hydraulic conductance is important for maintaining longer vase life, an important index for cut flower quality. Many factors, such as stomata performance, root water uptake efficiency, temperature, light quality and humidity, influence the efficiency of water transport in the soil-plant-atmosphere continuum.It has also been shown that the dimensions of the xylem conduits in the plant, such as the conduit length, diameter and density, are important for plant water transport. Therefore, the regulation of the xylem conduit size during xylogenesis is necessary for providing a particular hydraulic efficiency in a given environment. To understand the regulation of xylogenesis and the influence of the processes to produce xylem conduits of particular dimensions with specific hydraulic capacity, this thesis focuses on the Zinnia elegans tracheary element (TE) differentiation at the cellular level. It further considers the regulation of xylem conduit dimensions in whole plants by using drought stress and temperature as variable environmental factors.In Chapter 1, the mechanisms of plant water transport, as regulated by xylem conduit dimensions with consequent effect on plant quality, are reviewed. Also, the chapter provides general literature on xylem formation, Zinnia elegans as model for xylogenic research, and finally gives the outline of the thesis.In Chapter 2 , two cultivars of the Zinnia elegans cut flowers, 'Envy' and 'Purple Prince', were grown in soils with different water contents with increasing water stress levels: 70, 50 and 20 %(v/v) soil water content (SWC). Plant length increased with SWC. The hydraulic efficiency in the stems of cut flowers decreased with increasing water stress. The xylem conduit length was not different between Purple Prince cut flowers from the three different water stress levels. In the Envy cultivar, a significant difference in conduit length was found between plants from 20 and 50% (v/v) SWCs. The proportion of large-diameter conduits increased with decreasing drought stress, i.e., in cut flowers from both cultivars the proportion of large-diameter vessels was highest in the 70% (v/v) SWC and least in the 20% (v/v) SWC. This means that the decrease in hydraulic conductivity with water stress was largely due to the decrease in the diameter of the conduits making the conduit length less important. The vase life of the cut flowers correlated negatively with the diameter of the xylem conduits, confirming that small-diameter conduits are more efficient in overcoming embolism and therefore maintaining efficient water transport in the stems.In Chapter 3 , the role of average day temperature (ADT) and difference in day and night temperature (DIF) on the length of xylem elements and conduits, and fusion of the individual elements into conduits in planta were investigated. Plant length increased significantly with ADT between 17 and 25 o C. Opposite DIF treatments resulted in different plant length at 4 and 8 o C absolute DIF. The responses to temperature differences were similar in both Zinnia cultivars, although Purple Prince cultivar plants were always bigger. The maximal vessel length (L max ) and half vessel lengths (τ) both increased with increasing ADT, about 110-130% increase from 17 to 25 o C ADT. However, DIF had no effect on these conduit parameters. Measurements of average lengths of individual vessel elements from plants grown at average temperatures 17 and 25 o C showed about 10% and 20% increase in Envy and Purple Prince respectively. This change in vessel element length constitutes a small part of the overall change in whole conduit length, and therefore, it can be deduced that the amount of vessel element fusion is more important during formation of longer xylem conduits in the plant.In Chapter 4 , a method for establishing an in vitroZinnia elegans cell culture for differentiation into tracheary elements (TEs) is described. The xylogenic Zinnia system is rather unique for studying xylogenesis at the cellular level. It offers possibilities to study in detail the effects of certain factors important for regulating the xylogenesis process. The in vitro culture has been well standardized to eliminate the inconsistencies in TE differentiation that have been observed in the past. Additional methods for monitoring and measuring the important hallmarks of TE differentiation, including DNA laddering, vacuolar rupture, cellulose bands and lignin synthesis, have been treated in this section.In Chapter 5 , the effect of leaf osmolarity (LO) induced by different light intensities and electrical conductivity (EC) of soil-less plant culture, on the differentiation of TEs in cell cultures from the two cultivars, Envy and Purple Prince, was investigated. Both light intensity and EC correlated with LO with a similar response, although it was always higher in the Envy cultivar. By increasing the LO, the percentage of TEs (%TE) formed also increased, with a similar trend in cultures from both cultivars. About 60% increase in %TE was realized in the Purple Prince cultivar as compared to earlier reports by different authors. The LO of the starting material also correlated positively with the final size of the TE. This implies that the efficiency of the xylogenic Zinnia system can be improved by adaptations in the growth conditions for the starting material.In Chapter 6 , we investigated the effect of osmotic stress and timed application of NAA and BA (xylem differentiating phytohormones) on the TE differentiation in cultures from the two Zinnia cultivars. The %TE increased with increasing extracellular osmotic stress until 300 mOsm, after which any additional increase resulted in a diminishing %TE. The size of the TEs increased with decreasing extracellular osmolarity within the working range of 100 to 700 mOsm. These results were similar in the cultures from both cultivars. Application of NAA/BA induced a significant increase in the rate of cell division corresponding to a similar increase in TE differentiation. It is proposed that the increase in cell division may be beneficial in providing certain bioactive materials for the development of the TEs. Delayed application of NAA/BA reduced the %TE, but with a significant increase in TE size.In Chapter 7 , the role of programmed cell death (PCD) in determining the final size of the TEs and the %TE was investigated. Application of two protease inhibitors, a general caspase inhibitor (Zasp) and a cysteine protease inhibitor (E64), to xylogenic cultures from the two cultivars, caused a significant increase in the size of TEs but 65-300% decrease in %TE. There proved to be a significant delay or complete inhibition of the hallmarks of PCD, such as DNA laddering and vacuole collapse, in the cultures treated with the inhibitors. It was also found that the second stream of TE differentiation, common in non-inhibited xylogenic Zinnia cultures, was absent in cultures treated with 10nM or higher of each of the two inhibitors.The research experiments and their outcomes in this thesis range from fundamental xylogenesis at the cellular level to whole plant water transport performance. The overall discussion of the experimental approaches, results, and their practical implications is presented in Chapter 8 . This chapter also offers suggestions for future research.

The water status in plants is dependent on the xylem hydraulic conductance. In cut flowers, for example, the preservation of continuous hydraulic conductance is important for maintaining longer vase life, an important index for cut flower quality. Many factors, such as stomata performance, root water uptake efficiency, temperature, light quality and humidity, influence the efficiency of water transport in the soil-plant-atmosphere continuum.It has also been shown that the dimensions of the xylem conduits in the plant, such as the conduit length, diameter and density, are important for plant water transport. Therefore, the regulation of the xylem conduit size during xylogenesis is necessary for providing a particular hydraulic efficiency in a given environment. To understand the regulation of xylogenesis and the influence of the processes to produce xylem conduits of particular dimensions with specific hydraulic capacity, this thesis focuses on the Zinnia elegans tracheary element (TE) differentiation at the cellular level. It further considers the regulation of xylem conduit dimensions in whole plants by using drought stress and temperature as variable environmental factors.In Chapter 1, the mechanisms of plant water transport, as regulated by xylem conduit dimensions with consequent effect on plant quality, are reviewed. Also, the chapter provides general literature on xylem formation, Zinnia elegans as model for xylogenic research, and finally gives the outline of the thesis.In Chapter 2 , two cultivars of the Zinnia elegans cut flowers, 'Envy' and 'Purple Prince', were grown in soils with different water contents with increasing water stress levels: 70, 50 and 20 %(v/v) soil water content (SWC). Plant length increased with SWC. The hydraulic efficiency in the stems of cut flowers decreased with increasing water stress. The xylem conduit length was not different between Purple Prince cut flowers from the three different water stress levels. In the Envy cultivar, a significant difference in conduit length was found between plants from 20 and 50% (v/v) SWCs. The proportion of large-diameter conduits increased with decreasing drought stress, i.e., in cut flowers from both cultivars the proportion of large-diameter vessels was highest in the 70% (v/v) SWC and least in the 20% (v/v) SWC. This means that the decrease in hydraulic conductivity with water stress was largely due to the decrease in the diameter of the conduits making the conduit length less important. The vase life of the cut flowers correlated negatively with the diameter of the xylem conduits, confirming that small-diameter conduits are more efficient in overcoming embolism and therefore maintaining efficient water transport in the stems.In Chapter 3 , the role of average day temperature (ADT) and difference in day and night temperature (DIF) on the length of xylem elements and conduits, and fusion of the individual elements into conduits in planta were investigated. Plant length increased significantly with ADT between 17 and 25 o C. Opposite DIF treatments resulted in different plant length at 4 and 8 o C absolute DIF. The responses to temperature differences were similar in both Zinnia cultivars, although Purple Prince cultivar plants were always bigger. The maximal vessel length (L max ) and half vessel lengths (τ) both increased with increasing ADT, about 110-130% increase from 17 to 25 o C ADT. However, DIF had no effect on these conduit parameters. Measurements of average lengths of individual vessel elements from plants grown at average temperatures 17 and 25 o C showed about 10% and 20% increase in Envy and Purple Prince respectively. This change in vessel element length constitutes a small part of the overall change in whole conduit length, and therefore, it can be deduced that the amount of vessel element fusion is more important during formation of longer xylem conduits in the plant.In Chapter 4 , a method for establishing an in vitroZinnia elegans cell culture for differentiation into tracheary elements (TEs) is described. The xylogenic Zinnia system is rather unique for studying xylogenesis at the cellular level. It offers possibilities to study in detail the effects of certain factors important for regulating the xylogenesis process. The in vitro culture has been well standardized to eliminate the inconsistencies in TE differentiation that have been observed in the past. Additional methods for monitoring and measuring the important hallmarks of TE differentiation, including DNA laddering, vacuolar rupture, cellulose bands and lignin synthesis, have been treated in this section.In Chapter 5 , the effect of leaf osmolarity (LO) induced by different light intensities and electrical conductivity (EC) of soil-less plant culture, on the differentiation of TEs in cell cultures from the two cultivars, Envy and Purple Prince, was investigated. Both light intensity and EC correlated with LO with a similar response, although it was always higher in the Envy cultivar. By increasing the LO, the percentage of TEs (%TE) formed also increased, with a similar trend in cultures from both cultivars. About 60% increase in %TE was realized in the Purple Prince cultivar as compared to earlier reports by different authors. The LO of the starting material also correlated positively with the final size of the TE. This implies that the efficiency of the xylogenic Zinnia system can be improved by adaptations in the growth conditions for the starting material.In Chapter 6 , we investigated the effect of osmotic stress and timed application of NAA and BA (xylem differentiating phytohormones) on the TE differentiation in cultures from the two Zinnia cultivars. The %TE increased with increasing extracellular osmotic stress until 300 mOsm, after which any additional increase resulted in a diminishing %TE. The size of the TEs increased with decreasing extracellular osmolarity within the working range of 100 to 700 mOsm. These results were similar in the cultures from both cultivars. Application of NAA/BA induced a significant increase in the rate of cell division corresponding to a similar increase in TE differentiation. It is proposed that the increase in cell division may be beneficial in providing certain bioactive materials for the development of the TEs. Delayed application of NAA/BA reduced the %TE, but with a significant increase in TE size.In Chapter 7 , the role of programmed cell death (PCD) in determining the final size of the TEs and the %TE was investigated. Application of two protease inhibitors, a general caspase inhibitor (Zasp) and a cysteine protease inhibitor (E64), to xylogenic cultures from the two cultivars, caused a significant increase in the size of TEs but 65-300% decrease in %TE. There proved to be a significant delay or complete inhibition of the hallmarks of PCD, such as DNA laddering and vacuole collapse, in the cultures treated with the inhibitors. It was also found that the second stream of TE differentiation, common in non-inhibited xylogenic Zinnia cultures, was absent in cultures treated with 10nM or higher of each of the two inhibitors.The research experiments and their outcomes in this thesis range from fundamental xylogenesis at the cellular level to whole plant water transport performance. The overall discussion of the experimental approaches, results, and their practical implications is presented in Chapter 8 . This chapter also offers suggestions for future research.

Door ingrepen in de waterhuishouding is in een groot deel van Nederland de grondwaterstand gedaald, wat mede heeft geleid tot verdroging. Om effecten van ingrepen te kunnen kwantificeren is in drie gebieden met het model SIMGRO de verandering in grondwateraanvulling en grondwaterstanden berekend. Hiervoor zijn scenario's gedefinieerd en doorgerekend die betrekking hebben op ingrepen over de laatste veertig jaar. Het blijkt dat de invloed van de meteorologische omstandigheden op de grondwateraanvulling groter is dan welke ingreep in de waterhuishouding ook. Van de ingrepen heeft de veranderde ontwatering en afwatering verreweg het meeste effect op de grondwaterstanden.

In opdracht van waterschap Peel en Maasvallei is een onderzoek uitgevoerd naar de geohydrologische eigenschappen van het topsysteem. Het waterschap gebruikt deze informatie bij de beoordeling en advisering ten behoeve van infiltratievoorzieningen. Voor de beoordeling van deze voorziening zijn de doorlatendheid en de dikte van de deklaag van belang alsook het doorlaatvermogen van het onderliggende watervoerende pakket. Voor het gebiedsdekkend vaststellen van de eigenschappen is het gebied geschematiseerd in 60 eenheden op basis van bodemeigenschappen en opbouw diepere ondergrond. Aan deze eenheden is een k-waardetabel gekoppeld. Deze tabel is gebaseerd op beschikbare metingen en schattingen en aangevuld met metingen die in het kader van dit onderzoek zijn uitgevoerd. Naast k-waarden is een diktekaart van de deklaag vervaardigd op basis van bruikbare boringen. Het doorlaatvermogen van het eerste watervoerend pakket is afgeleid uit verschillende bronnen, waaronder pompproeven. Een belangrijk punt bij gebruik van de geïnventariseerde gegevens is de anisotropie van de deklaag als gevolg van het voorkomen van klei, leem of veenlagen

In opdracht van waterschap Peel en Maasvallei is een onderzoek uitgevoerd naar de geohydrologische eigenschappen van het topsysteem. Het waterschap gebruikt deze informatie bij de beoordeling en advisering ten behoeve van infiltratievoorzieningen. Voor de beoordeling van deze voorziening zijn de doorlatendheid en de dikte van de deklaag van belang alsook het doorlaatvermogen van het onderliggende watervoerende pakket. Voor het gebiedsdekkend vaststellen van de eigenschappen is het gebied geschematiseerd in 60 eenheden op basis van bodemeigenschappen en opbouw diepere ondergrond. Aan deze eenheden is een k-waardetabel gekoppeld. Deze tabel is gebaseerd op beschikbare metingen en schattingen en aangevuld met metingen die in het kader van dit onderzoek zijn uitgevoerd. Naast k-waarden is een diktekaart van de deklaag vervaardigd op basis van bruikbare boringen. Het doorlaatvermogen van het eerste watervoerend pakket is afgeleid uit verschillende bronnen, waaronder pompproeven. Een belangrijk punt bij gebruik van de geïnventariseerde gegevens is de anisotropie van de deklaag als gevolg van het voorkomen van klei, leem of veenlagen

Het doel van dit project is te onderzoeken hoe de relatie tussen grond- en oppervlaktewaterstand gebiedsdekkend kan worden beschreven in klei gebieden en hoe deze relatie gebruikt kan worden in een Gd-kartering. Een belangrijk aspect daarbij is de keuze van een meetnetopzet waarmee de relatie tussen grondwaterstand en oppervlaktewaterstand met een minimale meetinspanning zo goed mogelijk kan worden vastgesteld. In drie percelen in het komgebied van het land van Maas en Waal zijn de grond- en oppervlakte¬waterstand automatisch geregistreerd in raaien. De opbollings¬profielen in de drie raaien verschillen behoorlijk, ondanks hun korte onderlinge afstand in een vergelijkbaar landschap. De drainageweerstand, berekend uit het gemiddeld opbollings¬profiel over een stationaire periode, sluit het best aan bij de hydrologische definitie. De aldus berekende drainageweerstanden variëren met een factor twee, afhankelijk van de periode waarover berekening plaatsvindt. Ook de drainageweerstand, geschat uit gekalibreerde tijdreeksparameters, blijkt te variëren, afhankelijk van het kalibratiealgoritme en de tijdstap van het model en is daarom minder geschikt voor toepassing in een grootschalige Gd-kartering. Drainageweerstanden, geschat uit opbollingen over een veertiendaagse periode waarvan niet zeker is of stationariteit kan worden verondersteld, zijn vergelijkbaar met schattingen uit opbollingen over een stationaire periode. Hieruit blijkt dat de drainageweerstand ook op basis van slechts twee meettijdstippen mogelijk is. Dit is aantrekkelijk voor toepassing in een grootschalige Gd-kartering.

Het doel van dit project is te onderzoeken hoe de relatie tussen grond- en oppervlaktewaterstand gebiedsdekkend kan worden beschreven in klei gebieden en hoe deze relatie gebruikt kan worden in een Gd-kartering. Een belangrijk aspect daarbij is de keuze van een meetnetopzet waarmee de relatie tussen grondwaterstand en oppervlaktewaterstand met een minimale meetinspanning zo goed mogelijk kan worden vastgesteld. In drie percelen in het komgebied van het land van Maas en Waal zijn de grond- en oppervlakte¬waterstand automatisch geregistreerd in raaien. De opbollings¬profielen in de drie raaien verschillen behoorlijk, ondanks hun korte onderlinge afstand in een vergelijkbaar landschap. De drainageweerstand, berekend uit het gemiddeld opbollings¬profiel over een stationaire periode, sluit het best aan bij de hydrologische definitie. De aldus berekende drainageweerstanden variëren met een factor twee, afhankelijk van de periode waarover berekening plaatsvindt. Ook de drainageweerstand, geschat uit gekalibreerde tijdreeksparameters, blijkt te variëren, afhankelijk van het kalibratiealgoritme en de tijdstap van het model en is daarom minder geschikt voor toepassing in een grootschalige Gd-kartering. Drainageweerstanden, geschat uit opbollingen over een veertiendaagse periode waarvan niet zeker is of stationariteit kan worden verondersteld, zijn vergelijkbaar met schattingen uit opbollingen over een stationaire periode. Hieruit blijkt dat de drainageweerstand ook op basis van slechts twee meettijdstippen mogelijk is. Dit is aantrekkelijk voor toepassing in een grootschalige Gd-kartering.

The objective of this paper is to contribute to the ongoing discussion on strengths, weaknesses, opportunities and trends of existing modeling approaches in soil hydrology. We present a comprehensive case study of using integrated data to build a model of groundwater pollution for a watershed, and use this case study to illustrate current opportunities and problems related to quantifying soil variability with remote sensing, geophysical methods and topographic information

The importance of the unsaturated zone as an inextricable part of the hydrologic cycle has long been recognized. The root zone and the unsaturated sub-surface domain are chemically and biologically the most active zones. The interrelationships between soil, subsoil and surface waters make it unrealistic to treat the saturated and unsaturated zones and the discharge to surface waters separately. Point models describe vertical water flow in the saturated zone and possibly lateral flow by defining a sink term. To account for the influence of two- and three-dimensional water flow on the travel-time distribution a conceptualization of the flow field is required. A formulation for upscaling the groundwater flow field is presented which yields the average vertical flux as a key factor for describing the travel time implicitly. Analytical solutions are given for the upscaled description for the transport; they are applied to a simple model consisting of a cascade of reservoirs. The analytical approach given, which includes the main properties of the soil system as well as the drainage system, proves to be useful for the prediction of solute concentrations in exfiltrating groundwater. The use and significance of conceptual models is discussed as well as the opportunities of detailed mechanistic integrated models that treat the unsaturated/saturated zone, overland flow and surface water flow comprehensively. Some results of experimental field work on the assessment of drainage water quality impacts of agricultural land management are summarized. Strengths, weaknesses, opportunities and threats of different modeling approaches are discussed. The unsaturated zone is an essential link in the chain between land management practices and the ecological status of freshwaters.

The objective of this paper is to contribute to the ongoing discussion on strengths, weaknesses, opportunities and trends of existing modeling approaches in soil hydrology. We present a comprehensive case study of using integrated data to build a model of groundwater pollution for a watershed, and use this case study to illustrate current opportunities and problems related to quantifying soil variability with remote sensing, geophysical methods and topographic information

Voor de bodemfysische karakterisering van gronden in het waterschap Rijn & IJssel is gebruikt gemaakt van De Bodemkaart van Nederland, schaal 1 : 50 000 en verschillende detailbodem¬kaarten, schaal 1 : 10 000. Eenheden van bodemkaarten met bodemfysisch verwante eigenschappen zijn gegeneraliseerd tot bodemfysische eenheden. Van deze eenheden zijn gestan¬daardiseerde profielbeschrijvingen gemaakt, waarin de opeenvolging van de verschillende bodemhorizonten staan beschreven. De onderscheiden horizonten zijn vertaald naar bodem¬fysische bouwstenen uit de Staringreeks. Door deze link is het mogelijk de bodemfysische karakteristieken ruimtelijk weer te geven, en op die manier gebiedsdekkend toepasbaar te maken voor simulatiemodellen. Het resultaat bestaat uit 2 bodemfysische-eenhedenkaarten; één op basis van de Bodemkaart van Nederland, schaal 1 : 50 000, en één bodemfysische-eenhedenkaart op basis van de beschikbare detailbodemkaarten, schaal 1 : 10 00. Door het globale karakter van de gestandaardiseerde profielbeschrijvingen en de Staringreeks, is de informatie alleen geschikt voor toepassingen op regionaal niveau. Voor lokale toepassingen zijn meer gedetailleerde en gebiedspecifieke gegevens nodig.

Voor de bodemfysische karakterisering van gronden in het waterschap Rijn & IJssel is gebruikt gemaakt van De Bodemkaart van Nederland, schaal 1 : 50 000 en verschillende detailbodem¬kaarten, schaal 1 : 10 000. Eenheden van bodemkaarten met bodemfysisch verwante eigenschappen zijn gegeneraliseerd tot bodemfysische eenheden. Van deze eenheden zijn gestan¬daardiseerde profielbeschrijvingen gemaakt, waarin de opeenvolging van de verschillende bodemhorizonten staan beschreven. De onderscheiden horizonten zijn vertaald naar bodem¬fysische bouwstenen uit de Staringreeks. Door deze link is het mogelijk de bodemfysische karakteristieken ruimtelijk weer te geven, en op die manier gebiedsdekkend toepasbaar te maken voor simulatiemodellen. Het resultaat bestaat uit 2 bodemfysische-eenhedenkaarten; één op basis van de Bodemkaart van Nederland, schaal 1 : 50 000, en één bodemfysische-eenhedenkaart op basis van de beschikbare detailbodemkaarten, schaal 1 : 10 00. Door het globale karakter van de gestandaardiseerde profielbeschrijvingen en de Staringreeks, is de informatie alleen geschikt voor toepassingen op regionaal niveau. Voor lokale toepassingen zijn meer gedetailleerde en gebiedspecifieke gegevens nodig.