Nicholas Jarvis - Academia.edu (original) (raw)
Papers by Nicholas Jarvis
Hydrological Sciences Journal, 2003
The purpose of this study was to assess the degree of preferential flow in an unsaturated soil co... more The purpose of this study was to assess the degree of preferential flow in an unsaturated soil column using two different models: the dual-porosity model, MACRO, and the kinematic wave approach (KWA) based on boundary-layer flow theory. The soil column experiments consisted of six infiltrations with intensities varying from 15 to 101 mm h. Bromide solution was also infiltrated at
European Journal of Soil Science, 2015
ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, ... more ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near-saturated hydraulic conductivities in undisturbed soils with a global meta-database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta-databases may strongly over-estimate prediction performance unless they are validated against each individual data source separately. For such a source-wise cross-validation, we estimated the hydraulic conductivity at a tension of 10 cm (K10) and the saturated hydraulic conductivity (Ks) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K10 were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in-depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K10, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension-sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for Ks. The direction of the tension-sequence and the soil texture class were also important, with both coarse and fine-textured soils generally having larger Ks values than medium-textured soils.
The saturated and near-saturated hydraulic conductivity of soil is of key importance for modellin... more The saturated and near-saturated hydraulic conductivity of soil is of key importance for modelling water and solute fluxes in the vadose zone. Hydraulic conductivity measurements are cumbersome at the Darcy scale and practically impossible at larger scales where water and solute transport models are mostly applied. Hydraulic conductivity must therefore be estimated from proxy variables. Such pedotransfer functions are known to work decently well for e.g. water retention curves but rather poorly for near-saturated and saturated hydraulic conductivities. Recently, Weynants et al. (2009, Revisiting Vereecken pedotransfer functions: Introducing a closed-form hydraulic model. Vadose Zone Journal, 8, 86-95) reported a coefficients of determination of 0.25 (validation with an independent data set) for the saturated hydraulic conductivity from lab-measurements of Belgian soil samples. In our study, we trained boosted regression trees on a global meta-database containing tension-disk infiltr...
European Journal of Soil Science, 2015
ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, ... more ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near-saturated hydraulic conductivities in undisturbed soils with a global meta-database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta-databases may strongly over-estimate prediction performance unless they are validated against each individual data source separately. For such a source-wise cross-validation, we estimated the hydraulic conductivity at a tension of 10 cm (K10) and the saturated hydraulic conductivity (Ks) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K10 were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in-depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K10, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension-sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for Ks. The direction of the tension-sequence and the soil texture class were also important, with both coarse and fine-textured soils generally having larger Ks values than medium-textured soils.
Science of The Total Environment, 2015
Climate change is not only likely to improve conditions for crop production in Sweden, but also t... more Climate change is not only likely to improve conditions for crop production in Sweden, but also to increase weed pressure and the need for herbicides. This study aimed at assessing and contrasting the direct and indirect effects of climate change on herbicide leaching to groundwater in a major crop production region in south-west Sweden with the help of the regional pesticide fate and transport model MACRO-SE. We simulated 37 out of the 41 herbicides that are currently approved for use in Sweden on eight major crop types for the 24 most common soil types in the region. The results were aggregated accounting for the fractional coverage of the crop and the area sprayed with a particular herbicide. For simulations of the future, we used projections of five different climate models as model driving data and assessed three different future scenarios: (A) only changes in climate, (B) changes in climate and land-use (altered crop distribution), and (C) changes in climate, land-use, and an increase in herbicide use. The model successfully distinguished between leachable and non-leachable compounds (88% correctly classified) in a qualitative comparison against regional-scale monitoring data. Leaching was dominated by only a few herbicides and crops under current climate and agronomic conditions. The model simulations suggest that the direct effects of an increase in temperature, which enhances degradation, and precipitation which promotes leaching, cancel each other at a regional scale, resulting in a slight decrease in leachate concentrations in a future climate. However, the area at risk of groundwater contamination doubled when indirect effects of changes in land-use and herbicide use, were considered. We therefore concluded that it is important to consider the indirect effects of climate change alongside the direct effects and that effective mitigation strategies and strict regulation are required to secure future (drinking) water resources.
In risk assessments for contaminated soils an important part is to understand and to describe the... more In risk assessments for contaminated soils an important part is to understand and to describe the transport of metals in soils and groundwaters. This requires knowledge not only of the leaching patterns from the contamination source for the metals under consideration, but also of hydrological, geological and geochemical factors that affect the transport to nearby water systems through dilution and retardation processes. Different types of transport models can be applied, depending on the nature of the contaminant, on the nature of the medium (soil, groundwater, surface water, sediment), on hydrogeological conditions, and not least on the question to be answered. The most simplified transport models in use today for contaminated areas (used for example for calculations of guidance values) do not consider sorption of contaminants to the solid phase and hence not to any retardation during the transport through the saturated zone. Instead only dilution processes with groundwater are con...
Pesticide leaching from arable land constitutes a potential risk for contamination of ground and ... more Pesticide leaching from arable land constitutes a potential risk for contamination of ground and surface waters. Degradation and transport of pesticides in arable soils are influenced by both soil type, compound properties and application timings and are also strongly linked to weather and climate such as temperature and rainfall patterns. The assessment of pesticide leaching under climate change can give early indications of possible changes in pesticide leaching risks of importance for water pollution and serve as a basis for decision-making regarding the use of pesticides. Such an assessment requires detailed analyses of different sources of uncertainty that influence the results. The aim of this study was to assess the uncertainty related to climate scenario input data and to compare this to the parameter uncertainty of the pesticide leaching model. Furthermore, the influence of the choice of application timing on the leaching results was investigated. We used a modified version...
Hydrology and Earth System Sciences
The characteristics of the soil macropore network determine the potential for fast transport of a... more The characteristics of the soil macropore network determine the potential for fast transport of agrochemicals and contaminants through the soil. The objective of this study was to examine the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport. Experiments were carried out under near-saturated conditions on undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-D X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disc infiltrometer...
Near-saturated hydraulic conductivity exerts a critical control on water flow and solute transpor... more Near-saturated hydraulic conductivity exerts a critical control on water flow and solute transport through the vadose zone, yet very little is known concerning how it is influenced by various soil properties and site factors and attributes. Starting from the 1980's, tension infiltrometers or disc permeameters have become an increasingly popular method to measure near-saturated hydraulic conductivity in undisturbed soil. In this presentation, we describe the development and organization of a large database of tension infiltrometer measurements (n>700) collated from the published literature. The raw datasets were standardized and summarized using a modified Kozeny-Carman model of near-saturated hydraulic conductivity (Jarvis, N.J. 2008. Near-saturated hydraulic properties of macroporous soils. Vadose Zone Journal, 7, 1302-1310). This model was found to accurately describe near-saturated conductivity for this large dataset (92% of cases had R2 values larger than 0.9). We will sh...
Hydropedology, 2012
ABSTRACT Preferential flow is often thought of as a spatially and temporally highly variable and ... more ABSTRACT Preferential flow is often thought of as a spatially and temporally highly variable and random process and, as such, essentially unpredictable. This chapter discusses the experimental evidence accumulated during the last 20–30 years that suggests that such a view is too pessimistic. The chapter first presents a brief overview of methods to quantify preferential flow in soil and the characteristics of pore systems that control it. The influence of basic soil properties and site attributes on soil structure and preferential flow is then discussed. This is followed by an overview of the dominant flow and transport regimes found in the major soil types of the world, which is based on a comprehensive review and synthesis of the extensive literature. In the context of predictive applications of preferential flow models, the use of both continuous and class pedotransfer functions is then discussed. This is followed by a brief presentation of case studies dealing with the development and application of pesticide risk assessment and management tools that employ hydropedological concepts and approaches to account for macropore flow impacts at catchment and regional scales. The chapter concludes with a discussion of uncertainty and how to deal with it, and also makes some recommendations for future research directions that can help fill some of the remaining knowledge gaps.
Science of The Total Environment, 2015
Climate change is not only likely to improve conditions for crop production in Sweden, but also t... more Climate change is not only likely to improve conditions for crop production in Sweden, but also to increase weed pressure and the need for herbicides. This study aimed at assessing and contrasting the direct and indirect effects of climate change on herbicide leaching to groundwater in a major crop production region in south-west Sweden with the help of the regional pesticide fate and transport model MACRO-SE. We simulated 37 out of the 41 herbicides that are currently approved for use in Sweden on eight major crop types for the 24 most common soil types in the region. The results were aggregated accounting for the fractional coverage of the crop and the area sprayed with a particular herbicide. For simulations of the future, we used projections of five different climate models as model driving data and assessed three different future scenarios: (A) only changes in climate, (B) changes in climate and land-use (altered crop distribution), and (C) changes in climate, land-use, and an increase in herbicide use. The model successfully distinguished between leachable and non-leachable compounds (88% correctly classified) in a qualitative comparison against regional-scale monitoring data. Leaching was dominated by only a few herbicides and crops under current climate and agronomic conditions. The model simulations suggest that the direct effects of an increase in temperature, which enhances degradation, and precipitation which promotes leaching, cancel each other at a regional scale, resulting in a slight decrease in leachate concentrations in a future climate. However, the area at risk of groundwater contamination doubled when indirect effects of changes in land-use and herbicide use, were considered. We therefore concluded that it is important to consider the indirect effects of climate change alongside the direct effects and that effective mitigation strategies and strict regulation are required to secure future (drinking) water resources.
Soil and Tillage Research, 2009
Soil tillage has the potential to influence water flow and solute transport through the soil by c... more Soil tillage has the potential to influence water flow and solute transport through the soil by cutting continuous macropores which connect the soil surface to the subsoil. Tillage also affects soil organic carbon sequestration which may lead to different sorption and degradation properties depending on the long-term tillage practices. The objective of this study was to quantify the differences in
Soil Use and Management, 1986
Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large c... more Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large cores of Evesham clay soil were observed for periods up to 40 days under continuous ponding. A strong linear relationship (r 2= 0.94) found between these two variables was ...
Soil Use and Management, 2002
The dual porosity soil water and contaminant transport model MACRO was tested for its suitability... more The dual porosity soil water and contaminant transport model MACRO was tested for its suitability to represent water¯ows and leaching of phosphorus (P) through ®eld drains following spreading of slurry. These¯ows are characterized by very high loadings of P, including a high proportion in colloidally attached form, for about one week following winter spreading of slurry, followed by quite a rapid decline to the low background level. Use was made of the option in MACRO for representing colloid facilitated contaminant transport. The model simulates transport through macropores and soil matrix pores (micropores) of contaminant carrying colloids, as well as trapping of colloids by straining and ®ltration using an adaptation of standard ®ltration equations. Calibration involved selecting soil hydraulic parameters, colloid ®ltration coef®cients and P sorption characteristics for two soils from measured and literature values. Both P in solution and P attached to colloids were represented in simulated outputs. Reasonable agreement was found between simulated and measured water and leached P¯ows. Work with the model suggests that macroporē ow through the soil to ®eld drains of colloidally transported P is an important component of water pollution associated with slurry spreading
Science of The Total Environment, 2011
Degradation of pesticides in soils is both spatially variable and also one of the most sensitive ... more Degradation of pesticides in soils is both spatially variable and also one of the most sensitive factors determining losses to surface water and groundwater. To date, no general guidance is available on suitable approaches for dealing with spatial variation in pesticide degradation in catchment or regional scale modeling applications. The purpose of the study was therefore to study the influence of various soil physical, chemical and microbiological characteristics on pesticide persistence in the contrasting cultivated soils found in a small (13 km(2)) agricultural catchment in Sweden and to develop and test a simple model approach that could support catchment scale modeling. Persistence of bentazone, glyphosate and isoproturon was investigated in laboratory incubation experiments. Degradation rate constants were highly variable with coefficients of variation ranging between 42 and 64% for the three herbicides. Multiple linear regression analysis and Mallows Cp statistic were employed to select the best set of independent parameters accounting for the variation in degradation. Soil pH and the proportion of active microorganisms (r) together explained 69% of the variation in the bentazone degradation rate constant; the Freundlich sorption co-efficient (K(f)) and soil laccase activity together explained 88% of the variation in degradation rate of glyphosate, while soil pH was a significant predictor (p<0.05) for isoproturon persistence. However, correlations between many potential predictor variables made clear interpretations of the statistical analysis difficult. Multiplicative models based on two predictors chosen 'a priori', one accounting for microbial activity (e.g. microbial respiration, laccase activity or the surrogate variable soil organic carbon, SOC) and one accounting for the effects of sorption on bioavailability, showed promise to support predictions of degradation for large-scale modeling applications, explaining up to 50% of the variation in herbicide persistence.
Journal of Hydrology, 2006
Preferential flow through soil macropores in tile drained soils can significantly increase the ri... more Preferential flow through soil macropores in tile drained soils can significantly increase the risk of pollution of surface water bodies by agricultural chemicals such as pesticides. While many field studies have shown the importance of preferential flow in tile-drained fields, few have included detailed numerical modelling of the processes involved. The objective of this study was to compare four conceptually different preferential flow and/or transport approaches for their ability to simulate drainage and pesticide leaching to tile drains. The different approaches included an equilibrium approach using modified hydraulic properties near saturation, and three non-equilibrium approaches: a mobile-immobile solute transport model, a dual-porosity approach, and a dual-permeability formulation. They were implemented into the HYDRUS-2D software package. The model predictions were compared against measurements of drainage and pesticide concentrations made at an undulating, tile-drained field in southern Sweden (Näsbygård) during a period of 6 weeks following spray application of the herbicide MCPA.
Hydrology and Earth System Sciences, 2012
Estimating pesticide leaching risks at the regional scale requires the ability to completely para... more Estimating pesticide leaching risks at the regional scale requires the ability to completely parameterise a pesticide fate model using only survey data, such as soil and land-use maps. Such parameterisation usually rely on a set of lookup tables and (pedo)transfer functions, relating elementary soil and site properties to model param-5 eters. The aim of this paper is to describe and test a complete set of parameter estimation algorithms developed for the pesticide fate model MACRO, which accounts for preferential flow in soil macropores. We used tracer monitoring data from 16 lysimeter studies, carried out in three European countries, to evaluate the ability of MACRO and this "blind parameterisation" scheme to reproduce measured solute leaching at the 10 base of each lysimeter. We focused on the prediction of early tracer breakthrough due to preferential flow, because this is critical for pesticide leaching. We then calibrated a selected number of parameters in order to assess to what extent the prediction of water and solute leaching could be improved.
Hydrology and Earth System Sciences, 2012
Preferential flow is a widespread phenomenon that is known to strongly affect solute transport in... more Preferential flow is a widespread phenomenon that is known to strongly affect solute transport in soil, but our understanding and knowledge is still poor of the site factors and soil properties that promote it. To investigate these relationships, we assembled a database from the peer-reviewed literature containing information on 733 breakthrough curve experiments under steady-state flow conditions. Most of the collected experiments (585 of the 733 datasets) had been conducted on undisturbed soil columns, although some experiments on repacked soil, clean sands, and glass beads were also included. In addition to the apparent dispersivity, we focused our attention on three indicators of preferential solute transport: namely the 5 %-arrival time, the holdback factor, and the ratio of piston-flow and average transport velocities. Our results suggest that, in contrast to the 5 %-arrival time and the holdback factor, the piston-flow to transport velocity ratio is not related to preferential macropore transport but rather to the exclusion or retardation of the applied tracer. Confirming that the apparent longitudinal dispersivity is positively correlated with the travel distance of the tracer, our results also illustrate that this relationship is refined if the normalized 5 %-tracer arrival time is also taken into account. In particular, we found that the degree of preferential solute transport increases with apparent dispersivity and decreases with travel distance. A similar but weaker relationship was observed between apparent dispersivity, 5 %-tracer arrival time, and lateral observation scale, such that the degree of preferential transport increases with lateral observation scale. However, we also found that the travel distance and the lateral observation scale in the investigated dataset are correlated, which makes it difficult to distinguish their influence on these transport characteristics. We also found that the strength of preferential transport increased at larger flow rates and water saturations, which suggests that macropore flow was a more important flow mechanism than heterogeneous flow in the soil matrix. Nevertheless, our data show that heterogeneous flow in the soil matrix also occasionally leads to strong preferential transport. Furthermore, we show that preferential solute transport under steady-state flow depends on soil texture in a threshold-like manner: moderate to strong preferential transport was found to occur only for undisturbed soils that contain more than 8 % clay. Preferential flow characteristics were also absent for columns filled with glass beads, clean sands, or sieved soil. No clear effect of land use on the pattern of solute transport could be discerned, probably because the available dataset was too small and too strongly affected by cross-correlations with experimental conditions. Our results suggest that, in developing pedotransfer functions for solute transport properties of soils, it is critically important to account for travel distance, lateral observation scale, and water flow rate and saturation.
Hydrology and Earth System Sciences, 2013
Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity,... more Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity, K, in (eco)hydrological models ignore the effects of key site factors such as land use and climate and underplay the significant effects of soil structure on water flow at and near saturation. These limitations may introduce serious bias and error into predictions of terrestrial water balances and soil moisture status, and thus plant growth and rates of biogeochemical processes. To resolve these issues, we collated a new global database of hydraulic conductivity measured by tension infiltrometer under field conditions. The results of our analyses on this data set contrast markedly with those of existing algorithms used to estimate K. For example, saturated hydraulic conductivity, K s , in the topsoil (< 0.3 m depth) was found to be only weakly related to texture. Instead, the data suggests that K s depends more strongly on bulk density, organic carbon content and land use. In this respect, organic carbon was negatively correlated with K s , presumably due to water repellency, while K s at arable sites was, on average, ca. 2-3 times smaller than under natural vegetation, forests and perennial agriculture. The data also clearly demonstrates that clay soils have smaller K in the soil matrix and thus a larger contribution of soil macropores to K at and near saturation.
Hydrological Sciences Journal, 2003
The purpose of this study was to assess the degree of preferential flow in an unsaturated soil co... more The purpose of this study was to assess the degree of preferential flow in an unsaturated soil column using two different models: the dual-porosity model, MACRO, and the kinematic wave approach (KWA) based on boundary-layer flow theory. The soil column experiments consisted of six infiltrations with intensities varying from 15 to 101 mm h. Bromide solution was also infiltrated at
European Journal of Soil Science, 2015
ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, ... more ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near-saturated hydraulic conductivities in undisturbed soils with a global meta-database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta-databases may strongly over-estimate prediction performance unless they are validated against each individual data source separately. For such a source-wise cross-validation, we estimated the hydraulic conductivity at a tension of 10 cm (K10) and the saturated hydraulic conductivity (Ks) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K10 were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in-depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K10, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension-sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for Ks. The direction of the tension-sequence and the soil texture class were also important, with both coarse and fine-textured soils generally having larger Ks values than medium-textured soils.
The saturated and near-saturated hydraulic conductivity of soil is of key importance for modellin... more The saturated and near-saturated hydraulic conductivity of soil is of key importance for modelling water and solute fluxes in the vadose zone. Hydraulic conductivity measurements are cumbersome at the Darcy scale and practically impossible at larger scales where water and solute transport models are mostly applied. Hydraulic conductivity must therefore be estimated from proxy variables. Such pedotransfer functions are known to work decently well for e.g. water retention curves but rather poorly for near-saturated and saturated hydraulic conductivities. Recently, Weynants et al. (2009, Revisiting Vereecken pedotransfer functions: Introducing a closed-form hydraulic model. Vadose Zone Journal, 8, 86-95) reported a coefficients of determination of 0.25 (validation with an independent data set) for the saturated hydraulic conductivity from lab-measurements of Belgian soil samples. In our study, we trained boosted regression trees on a global meta-database containing tension-disk infiltr...
European Journal of Soil Science, 2015
ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, ... more ABSTRACT Hydraulic conductivity at and near saturation is difficult to predict. We investigated, for the first time, the potential of boosted regression trees to identify the key factors that determine saturated and near-saturated hydraulic conductivities in undisturbed soils with a global meta-database of tension infiltrometer measurements. Our results demonstrate that pedotransfer functions developed from meta-databases may strongly over-estimate prediction performance unless they are validated against each individual data source separately. For such a source-wise cross-validation, we estimated the hydraulic conductivity at a tension of 10 cm (K10) and the saturated hydraulic conductivity (Ks) with coefficients of determination of 0.36 and 0.15, respectively. The most important predictors for K10 were the average annual precipitation and temperature at the measurement location, which are key variables for pedogenesis and constrain soil management. More research is required for the in-depth interpretation of their influence on hydraulic conductivity. The soil clay and organic carbon contents were also important predictors of K10, with hydraulic conductivity decreasing as organic carbon contents increased up to 1.5% and as clay contents increased between about 10 and 40%. The direction of the tension-sequence with which the infiltrometer data were collected was also a significant predictor. Land use and bulk density were the most important predictors for Ks. The direction of the tension-sequence and the soil texture class were also important, with both coarse and fine-textured soils generally having larger Ks values than medium-textured soils.
Science of The Total Environment, 2015
Climate change is not only likely to improve conditions for crop production in Sweden, but also t... more Climate change is not only likely to improve conditions for crop production in Sweden, but also to increase weed pressure and the need for herbicides. This study aimed at assessing and contrasting the direct and indirect effects of climate change on herbicide leaching to groundwater in a major crop production region in south-west Sweden with the help of the regional pesticide fate and transport model MACRO-SE. We simulated 37 out of the 41 herbicides that are currently approved for use in Sweden on eight major crop types for the 24 most common soil types in the region. The results were aggregated accounting for the fractional coverage of the crop and the area sprayed with a particular herbicide. For simulations of the future, we used projections of five different climate models as model driving data and assessed three different future scenarios: (A) only changes in climate, (B) changes in climate and land-use (altered crop distribution), and (C) changes in climate, land-use, and an increase in herbicide use. The model successfully distinguished between leachable and non-leachable compounds (88% correctly classified) in a qualitative comparison against regional-scale monitoring data. Leaching was dominated by only a few herbicides and crops under current climate and agronomic conditions. The model simulations suggest that the direct effects of an increase in temperature, which enhances degradation, and precipitation which promotes leaching, cancel each other at a regional scale, resulting in a slight decrease in leachate concentrations in a future climate. However, the area at risk of groundwater contamination doubled when indirect effects of changes in land-use and herbicide use, were considered. We therefore concluded that it is important to consider the indirect effects of climate change alongside the direct effects and that effective mitigation strategies and strict regulation are required to secure future (drinking) water resources.
In risk assessments for contaminated soils an important part is to understand and to describe the... more In risk assessments for contaminated soils an important part is to understand and to describe the transport of metals in soils and groundwaters. This requires knowledge not only of the leaching patterns from the contamination source for the metals under consideration, but also of hydrological, geological and geochemical factors that affect the transport to nearby water systems through dilution and retardation processes. Different types of transport models can be applied, depending on the nature of the contaminant, on the nature of the medium (soil, groundwater, surface water, sediment), on hydrogeological conditions, and not least on the question to be answered. The most simplified transport models in use today for contaminated areas (used for example for calculations of guidance values) do not consider sorption of contaminants to the solid phase and hence not to any retardation during the transport through the saturated zone. Instead only dilution processes with groundwater are con...
Pesticide leaching from arable land constitutes a potential risk for contamination of ground and ... more Pesticide leaching from arable land constitutes a potential risk for contamination of ground and surface waters. Degradation and transport of pesticides in arable soils are influenced by both soil type, compound properties and application timings and are also strongly linked to weather and climate such as temperature and rainfall patterns. The assessment of pesticide leaching under climate change can give early indications of possible changes in pesticide leaching risks of importance for water pollution and serve as a basis for decision-making regarding the use of pesticides. Such an assessment requires detailed analyses of different sources of uncertainty that influence the results. The aim of this study was to assess the uncertainty related to climate scenario input data and to compare this to the parameter uncertainty of the pesticide leaching model. Furthermore, the influence of the choice of application timing on the leaching results was investigated. We used a modified version...
Hydrology and Earth System Sciences
The characteristics of the soil macropore network determine the potential for fast transport of a... more The characteristics of the soil macropore network determine the potential for fast transport of agrochemicals and contaminants through the soil. The objective of this study was to examine the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport. Experiments were carried out under near-saturated conditions on undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-D X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disc infiltrometer...
Near-saturated hydraulic conductivity exerts a critical control on water flow and solute transpor... more Near-saturated hydraulic conductivity exerts a critical control on water flow and solute transport through the vadose zone, yet very little is known concerning how it is influenced by various soil properties and site factors and attributes. Starting from the 1980's, tension infiltrometers or disc permeameters have become an increasingly popular method to measure near-saturated hydraulic conductivity in undisturbed soil. In this presentation, we describe the development and organization of a large database of tension infiltrometer measurements (n>700) collated from the published literature. The raw datasets were standardized and summarized using a modified Kozeny-Carman model of near-saturated hydraulic conductivity (Jarvis, N.J. 2008. Near-saturated hydraulic properties of macroporous soils. Vadose Zone Journal, 7, 1302-1310). This model was found to accurately describe near-saturated conductivity for this large dataset (92% of cases had R2 values larger than 0.9). We will sh...
Hydropedology, 2012
ABSTRACT Preferential flow is often thought of as a spatially and temporally highly variable and ... more ABSTRACT Preferential flow is often thought of as a spatially and temporally highly variable and random process and, as such, essentially unpredictable. This chapter discusses the experimental evidence accumulated during the last 20–30 years that suggests that such a view is too pessimistic. The chapter first presents a brief overview of methods to quantify preferential flow in soil and the characteristics of pore systems that control it. The influence of basic soil properties and site attributes on soil structure and preferential flow is then discussed. This is followed by an overview of the dominant flow and transport regimes found in the major soil types of the world, which is based on a comprehensive review and synthesis of the extensive literature. In the context of predictive applications of preferential flow models, the use of both continuous and class pedotransfer functions is then discussed. This is followed by a brief presentation of case studies dealing with the development and application of pesticide risk assessment and management tools that employ hydropedological concepts and approaches to account for macropore flow impacts at catchment and regional scales. The chapter concludes with a discussion of uncertainty and how to deal with it, and also makes some recommendations for future research directions that can help fill some of the remaining knowledge gaps.
Science of The Total Environment, 2015
Climate change is not only likely to improve conditions for crop production in Sweden, but also t... more Climate change is not only likely to improve conditions for crop production in Sweden, but also to increase weed pressure and the need for herbicides. This study aimed at assessing and contrasting the direct and indirect effects of climate change on herbicide leaching to groundwater in a major crop production region in south-west Sweden with the help of the regional pesticide fate and transport model MACRO-SE. We simulated 37 out of the 41 herbicides that are currently approved for use in Sweden on eight major crop types for the 24 most common soil types in the region. The results were aggregated accounting for the fractional coverage of the crop and the area sprayed with a particular herbicide. For simulations of the future, we used projections of five different climate models as model driving data and assessed three different future scenarios: (A) only changes in climate, (B) changes in climate and land-use (altered crop distribution), and (C) changes in climate, land-use, and an increase in herbicide use. The model successfully distinguished between leachable and non-leachable compounds (88% correctly classified) in a qualitative comparison against regional-scale monitoring data. Leaching was dominated by only a few herbicides and crops under current climate and agronomic conditions. The model simulations suggest that the direct effects of an increase in temperature, which enhances degradation, and precipitation which promotes leaching, cancel each other at a regional scale, resulting in a slight decrease in leachate concentrations in a future climate. However, the area at risk of groundwater contamination doubled when indirect effects of changes in land-use and herbicide use, were considered. We therefore concluded that it is important to consider the indirect effects of climate change alongside the direct effects and that effective mitigation strategies and strict regulation are required to secure future (drinking) water resources.
Soil and Tillage Research, 2009
Soil tillage has the potential to influence water flow and solute transport through the soil by c... more Soil tillage has the potential to influence water flow and solute transport through the soil by cutting continuous macropores which connect the soil surface to the subsoil. Tillage also affects soil organic carbon sequestration which may lead to different sorption and degradation properties depending on the long-term tillage practices. The objective of this study was to quantify the differences in
Soil Use and Management, 1986
Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large c... more Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large cores of Evesham clay soil were observed for periods up to 40 days under continuous ponding. A strong linear relationship (r 2= 0.94) found between these two variables was ...
Soil Use and Management, 2002
The dual porosity soil water and contaminant transport model MACRO was tested for its suitability... more The dual porosity soil water and contaminant transport model MACRO was tested for its suitability to represent water¯ows and leaching of phosphorus (P) through ®eld drains following spreading of slurry. These¯ows are characterized by very high loadings of P, including a high proportion in colloidally attached form, for about one week following winter spreading of slurry, followed by quite a rapid decline to the low background level. Use was made of the option in MACRO for representing colloid facilitated contaminant transport. The model simulates transport through macropores and soil matrix pores (micropores) of contaminant carrying colloids, as well as trapping of colloids by straining and ®ltration using an adaptation of standard ®ltration equations. Calibration involved selecting soil hydraulic parameters, colloid ®ltration coef®cients and P sorption characteristics for two soils from measured and literature values. Both P in solution and P attached to colloids were represented in simulated outputs. Reasonable agreement was found between simulated and measured water and leached P¯ows. Work with the model suggests that macroporē ow through the soil to ®eld drains of colloidally transported P is an important component of water pollution associated with slurry spreading
Science of The Total Environment, 2011
Degradation of pesticides in soils is both spatially variable and also one of the most sensitive ... more Degradation of pesticides in soils is both spatially variable and also one of the most sensitive factors determining losses to surface water and groundwater. To date, no general guidance is available on suitable approaches for dealing with spatial variation in pesticide degradation in catchment or regional scale modeling applications. The purpose of the study was therefore to study the influence of various soil physical, chemical and microbiological characteristics on pesticide persistence in the contrasting cultivated soils found in a small (13 km(2)) agricultural catchment in Sweden and to develop and test a simple model approach that could support catchment scale modeling. Persistence of bentazone, glyphosate and isoproturon was investigated in laboratory incubation experiments. Degradation rate constants were highly variable with coefficients of variation ranging between 42 and 64% for the three herbicides. Multiple linear regression analysis and Mallows Cp statistic were employed to select the best set of independent parameters accounting for the variation in degradation. Soil pH and the proportion of active microorganisms (r) together explained 69% of the variation in the bentazone degradation rate constant; the Freundlich sorption co-efficient (K(f)) and soil laccase activity together explained 88% of the variation in degradation rate of glyphosate, while soil pH was a significant predictor (p<0.05) for isoproturon persistence. However, correlations between many potential predictor variables made clear interpretations of the statistical analysis difficult. Multiplicative models based on two predictors chosen 'a priori', one accounting for microbial activity (e.g. microbial respiration, laccase activity or the surrogate variable soil organic carbon, SOC) and one accounting for the effects of sorption on bioavailability, showed promise to support predictions of degradation for large-scale modeling applications, explaining up to 50% of the variation in herbicide persistence.
Journal of Hydrology, 2006
Preferential flow through soil macropores in tile drained soils can significantly increase the ri... more Preferential flow through soil macropores in tile drained soils can significantly increase the risk of pollution of surface water bodies by agricultural chemicals such as pesticides. While many field studies have shown the importance of preferential flow in tile-drained fields, few have included detailed numerical modelling of the processes involved. The objective of this study was to compare four conceptually different preferential flow and/or transport approaches for their ability to simulate drainage and pesticide leaching to tile drains. The different approaches included an equilibrium approach using modified hydraulic properties near saturation, and three non-equilibrium approaches: a mobile-immobile solute transport model, a dual-porosity approach, and a dual-permeability formulation. They were implemented into the HYDRUS-2D software package. The model predictions were compared against measurements of drainage and pesticide concentrations made at an undulating, tile-drained field in southern Sweden (Näsbygård) during a period of 6 weeks following spray application of the herbicide MCPA.
Hydrology and Earth System Sciences, 2012
Estimating pesticide leaching risks at the regional scale requires the ability to completely para... more Estimating pesticide leaching risks at the regional scale requires the ability to completely parameterise a pesticide fate model using only survey data, such as soil and land-use maps. Such parameterisation usually rely on a set of lookup tables and (pedo)transfer functions, relating elementary soil and site properties to model param-5 eters. The aim of this paper is to describe and test a complete set of parameter estimation algorithms developed for the pesticide fate model MACRO, which accounts for preferential flow in soil macropores. We used tracer monitoring data from 16 lysimeter studies, carried out in three European countries, to evaluate the ability of MACRO and this "blind parameterisation" scheme to reproduce measured solute leaching at the 10 base of each lysimeter. We focused on the prediction of early tracer breakthrough due to preferential flow, because this is critical for pesticide leaching. We then calibrated a selected number of parameters in order to assess to what extent the prediction of water and solute leaching could be improved.
Hydrology and Earth System Sciences, 2012
Preferential flow is a widespread phenomenon that is known to strongly affect solute transport in... more Preferential flow is a widespread phenomenon that is known to strongly affect solute transport in soil, but our understanding and knowledge is still poor of the site factors and soil properties that promote it. To investigate these relationships, we assembled a database from the peer-reviewed literature containing information on 733 breakthrough curve experiments under steady-state flow conditions. Most of the collected experiments (585 of the 733 datasets) had been conducted on undisturbed soil columns, although some experiments on repacked soil, clean sands, and glass beads were also included. In addition to the apparent dispersivity, we focused our attention on three indicators of preferential solute transport: namely the 5 %-arrival time, the holdback factor, and the ratio of piston-flow and average transport velocities. Our results suggest that, in contrast to the 5 %-arrival time and the holdback factor, the piston-flow to transport velocity ratio is not related to preferential macropore transport but rather to the exclusion or retardation of the applied tracer. Confirming that the apparent longitudinal dispersivity is positively correlated with the travel distance of the tracer, our results also illustrate that this relationship is refined if the normalized 5 %-tracer arrival time is also taken into account. In particular, we found that the degree of preferential solute transport increases with apparent dispersivity and decreases with travel distance. A similar but weaker relationship was observed between apparent dispersivity, 5 %-tracer arrival time, and lateral observation scale, such that the degree of preferential transport increases with lateral observation scale. However, we also found that the travel distance and the lateral observation scale in the investigated dataset are correlated, which makes it difficult to distinguish their influence on these transport characteristics. We also found that the strength of preferential transport increased at larger flow rates and water saturations, which suggests that macropore flow was a more important flow mechanism than heterogeneous flow in the soil matrix. Nevertheless, our data show that heterogeneous flow in the soil matrix also occasionally leads to strong preferential transport. Furthermore, we show that preferential solute transport under steady-state flow depends on soil texture in a threshold-like manner: moderate to strong preferential transport was found to occur only for undisturbed soils that contain more than 8 % clay. Preferential flow characteristics were also absent for columns filled with glass beads, clean sands, or sieved soil. No clear effect of land use on the pattern of solute transport could be discerned, probably because the available dataset was too small and too strongly affected by cross-correlations with experimental conditions. Our results suggest that, in developing pedotransfer functions for solute transport properties of soils, it is critically important to account for travel distance, lateral observation scale, and water flow rate and saturation.
Hydrology and Earth System Sciences, 2013
Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity,... more Due to inadequate data support, existing algorithms used to estimate soil hydraulic conductivity, K, in (eco)hydrological models ignore the effects of key site factors such as land use and climate and underplay the significant effects of soil structure on water flow at and near saturation. These limitations may introduce serious bias and error into predictions of terrestrial water balances and soil moisture status, and thus plant growth and rates of biogeochemical processes. To resolve these issues, we collated a new global database of hydraulic conductivity measured by tension infiltrometer under field conditions. The results of our analyses on this data set contrast markedly with those of existing algorithms used to estimate K. For example, saturated hydraulic conductivity, K s , in the topsoil (< 0.3 m depth) was found to be only weakly related to texture. Instead, the data suggests that K s depends more strongly on bulk density, organic carbon content and land use. In this respect, organic carbon was negatively correlated with K s , presumably due to water repellency, while K s at arable sites was, on average, ca. 2-3 times smaller than under natural vegetation, forests and perennial agriculture. The data also clearly demonstrates that clay soils have smaller K in the soil matrix and thus a larger contribution of soil macropores to K at and near saturation.