29 research outputs found

    Impact of climate, soil properties and grassland cover on soil water repellency

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    Numerous soil water repellency (SWR) studies have investigated the possible causes of this temporal phenomenon, yet there remains a lack of knowledge on the order of importance of the main driving forces of SWR in the context of changing environmental conditions under grassland ecosystems. To study the separate and combined effects of soil texture, climate, and grassland cover type on inducing or altering SWR, four sites from different climatic and soil regions were selected: Ciavolo (CI, IT), Cs´olyosp´alos (CSP, HU), Pwllpeiran (PW, UK), Sekule (SE, SK). The investigated parameters were the extent (determined by repellency indices RI, RIc and RIm) and persistence (determined by water drop penetration time (WDPT) and water repellency cessation time, WRCT) of SWR, as well as field water (Sw) and ethanol (Se) sorptivity, water sorptivity of hydrophobic soil state (Swh) water sorptivity of nearly wettable soil state (Sww) and field hydraulic conductivity (K). Our findings showed an area of land has a greater likelihood of being water repellent if it has a sandy soil texture and/or a high frequency of prolonged drought events. Water infiltration was positively correlated with all the sorptivities (r = 0.32–0.88), but was mostly negatively correlated with RI (r = – 0.54 at CI), WDPT (r = – 0.47 at CI) and WRCT (r = – 0.58 at CI). The importance of natural and synanthropized vegetation covers with regards to SWR was not coherent; moving to regions having coarser texture or moving to drier climatic zones led to higher risk of SWR conditions. Climate change has been predicted to lead to more frequent extreme weather events and prolonged dry periods across Europe, which will most likely increase the extent of SWR-affected areas and increase the role of SWR in water management of grassland ecosystems. Therefore, there is a need to determine SWR risk zones to prevent decreases in soil moisture content, soil fertility, carbon and nitrogen sink potentials, as well as biomass production of the related agro-ecosystems

    Capturing 3D Water Flow in Rooted Soil by Ultra fast Neutron Tomography

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    Dutch Experience in Irrigation Water Management Modelling

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    Modeling the soil-water-crop atmosphere system to improve agricultural water management in arid zones (SWATRE); Groundwater approach to drainage design in irrigated agriculture (SGMP); Computer Program for flume and weir design (FLUME 3.0); A hydrodynamic model in the design of operational controllers for water systems (MODIS/MATLAB); Decision support simulation model for water management at a regional and national scale (SIWARE); Management of water delivery systems (RIBASIM/OMIS); A water allocation, scheduling, and monitoring program (WASAM); and Irrigation agencies, farmers and computational decision support tools

    Sustainability of irrigated agriculture under salinity pressure – A study in semiarid Tunisia

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    In semiarid and arid Tunisia, water quality and agricultural practices are the major contributing factors to the degradation of soil resources threatening the sustainability of irrigation systems and agricultural productivity. Nowadays, about 50% of the total irrigated areas in Tunisia are considered at high risk for salinization. The aim of this thesis was to study soil management and salinity relationships in order to assure sustainable irrigated agriculture in areas under salinity pressure. To prevent further soil degradation, farmers and rural development officers need guidance and better tools for the measurement, prediction, and monitoring of soil salinity at different observation scales, and associated agronomical strategy. Field experiments were performed in semi-arid Nabeul (sandy soil), semi-arid Kalâat Landalous (clay soil), and the desertic Fatnassa oasis (gypsiferous soil). The longest observation period represented 17 years. Besides field studies, laboratory experiments were used to develop accurate soil salinity measurements and prediction techniques. In saline gypsiferous soil, the WET sensor can give similar accuracy of soil salinity as the TDR if calibrated values of the soil parameters are used instead of standard values. At the Fatnassa oasis scale, the predicted values of ECe and depth of shallow groundwater Dgw using electromagnetic induction EM-38 were found to be in agreement with observed values with acceptable accuracy. At Kalâat Landalous (1400 ha), the applicability of artificial neural network (ANN) models for predicting the spatial soil salinity (ECe) was found to be better than multivariate linear regression (MLR) models. In semi-arid and desertic Tunisia, irrigation and drainage reduce soil salinity and dilute the shallow groundwater. However, the ECgw has a larger impact than soil salinity variation on salt balance. Based on the findings related to variation in the spatial and temporal soil and groundwater properties, soil salinization factors were identified and the level of soil “salinization risk unit” (SRU) was developed. The groundwater properties, especially the Dgw, could be considered as the main cause of soil salinization risk in arid Tunisia. However, under an efficient drainage network and water management, the soil salinization could be considered as a reversible process. The SRU mapping can be used by both land planners and farmers to make appropriate decisions related to crop production and soil and water management

    Stochastic representation of material heterogeneity and its effects on flow: applications in soils of mixed wettabilities

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    This work presents an investigation into the modelling of the hydraulic behaviour of heterogeneous soils of mixed wettabilities. The model represents moisture transfer of a liquid phase, and can account for the highly non-uniform nature of unsaturated flow in soil due to the presence of strong heterogeneity. This is accounted for with Gaussian random fields to represent an arbitrary number of spatially varying material properties. The theoretical formulations are presented to model this complex behaviour, as well as their numerical solutions which form the foundation of the developed model. The chosen method of random field generation is also investigated in terms of reducing the error in the correlated structures near the domain boundaries, as well as removing the need to solve over an extended domain. Methods to account for water repellency in soil are also given, such that the exaggerated flow behaviour it exhibits in relation to wettable unsaturated soil can be represented. Validation of the model was conducted through representing field tracer experiments to assess the ability of the model to predict suitable vertical profiles of dye coverage. This was conducted for both wettable and water repellent soil, and quantified through confidence intervals such that a very low number of simulations was able to describe the overall model response to a high level of confidence. The following conclusions can be drawn. The inclusion of material heterogeneity is crucial in representing complex unstable flow processes in soil of any wettability. The non-linear constitutive behaviour of the material that was predicted by the model simulations would be difficult to account for without spatial variability of material parameters. Similarly, the applied field generation method is a fast way to introduce this, and the proposed method of error reduction in the correlation structure is suitable for complex domains. The proposed methods to account for hydrophobicity based on the soil water retention curve are sufficient to allow unstable flow to develop. The similarity in finger characteristics of both the wettable and water repellent cases with the experimental observations suggest the model is more than sufficient in representing the complex flow behaviour that both can exhibit

    SWAP Version 3.2. Theory description and user manual

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    SWAP 3.2 simulates transport of water, solutes and heat in the vadose zone. It describes a domain from the top of canopy into the groundwater which may be in interaction with a surface water system. The program has been developed by Alterra and Wageningen University, and is designed to simulate transport processes at field scale and during whole growing seasons. This is a new release with special emphasis on numerical stability, macro pore flow, and options for detailed meteorological input and linkage to other models. This manual describes the theoretical background, model use, input requirements and output tables

    Soil response to acid deposition at different regional scales : field and laboratory data, critical loads and model predictions

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    Enhanced soil, ground water and surface water acidification by elevated deposition of S and N compounds is one of the most important large-scale environmental problems today. This thesis deals with the quantification of:(i) natural and man-induced sources of acidification in agricultural soils and forest soils in the Netherlands;(ii) present impacts of atmospheric S and N deposition on the solution chemistry of acid sandy forest soils in the Netherlands;(iii) various buffermechanisms (i.e. mineral weathering, cation exchange and AI dissolution) in acid sandy soils in the Netherlands;(iv) average critical deposition levels (loads) for N and acidity (N and S) for forests, heathlands, ground water and surface water in the Netherlands;(v) spatial variability in critical loads for N, S and acidity and the degree by which these loads are exceeded at present on forests in the Netherlands and in Europe;(vi) long-term impacts of acidic deposition on representative non-agricultural soils;(vii) spatial variability in long-term impacts of acidic deposition on forest soils in the Netherlands and in Europe. Quantification was performed on the basis of interpretation of literature information, combined with field research (i and ii), laboratory research (iii), and model research, (iv, v, vi and vii). In order to derive critical loads, steady-state soil models were developed, i.e. a one-layer model (START) for application on a European scale and a multi-layer model (MACAL) for application on a national scale. Similarly, two dynamic soil models were developed to assess the long-term soil response to acidic deposition, i.e. a onelayer model (SMART) for application in Europe and a multi-layer model (RESAM) for application in the Netherlands.Results showed that:(i) the contribution of acid deposition to soil acidificatiom in the Netherlands is dominant in non- calcareous forest soils (≥80%), intermediate in non-calcareous agricultural soils (≤50%) and minor in calcareous soils (≤20%);(ii) S0 4 behaves conservative in Dutch forest soils, whereas N is largely retained. Despite the high N deposition, actual soil acidification, which is mainly manifested by leaching of AI associated with SO 4 and NO 3 leaching, is dominantly caused by S deposition;(iii) dissolution of AI from secondary inorganic AI compounds is the dominant buffermechanism in acid sandy (forest) soils. The dissolution rate of AI can be described well as a function of the secondary AI pool and the degree of undersaturation with respect to gibbsite;(iv) average critical N loads for forests, heathlands, ground waters and surface waters in the Netherlands generally vary between 500 mol c ha -1yr -1('sensitive' heathlands and surface waters) and 3600 mol c ha -1yr -1('insensitive' ground waters). Average critical acid loads are generally lower and range between 400 mol c ha -1yr -1('sensitive' ground- and surface waters) to 1700 mol c ha -1yr -1('insensitive' forests and ground waters);(v) critical loads are largely exceeded in Central and Western Europe both in N (up to 3500 mol c ha -1yr -1) and S (up to 12000 mol c ha -1yr -1). In the Netherlands largest exceedances occur in areas with intensive animal husbandry. There emission reductions of more than 80% are needed to meet the critical loads;(vi) long-term continuation of present atmospheric deposition causes a depletion of the pool of secondary AI compounds, both in forest soils and dune soils of the Netherlands, leading to extremely low pH values. However, reduction of atmospheric deposition levels leads to a fast improvement of the soil solution quality (decreased concentrations in SO 4 , NO 3 and AI and increased pH);(vii) deposition scenarios including current reduction plans with respect to S and N emission lead to an improvement in the soil solution quality below forests in the Netherlands, but not in Europe

    How mucilage affects water flow in soils

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    Die Wurzelwasseraufnahme aus dem Boden wird durch die Rhizosphäre beeinflusst. Die Rhizosphäre ist eine dünne Bodenschicht, die sich um Wurzeln herum bildet. Die Rhizosphäre wird durch Mucilage beeinflusst. Mucilage ist ein polymeres Gel, was von Wurzeln abgesondert wird und vor allem die hydraulischen Eigenschaften der Rhizosphäre verändert. Wenn es im Kontakt mit Wasser ist, kann Mucilage große Mengen an Wasser aufnehmen, aber wenn es trocken ist, wird seine Oberfläche hydrophob. Hier konzentrieren wir uns auf den Effekt von Mucilage auf die hydraulischen Eigenschaften des Bodens. Zunächst präsentieren wir experimentelle und numerische Studien, die die hydraulischen Prozesse in der Rhizosphäre nach der Bewässerung von trockenem Boden beschreiben. Bei Mucilagekonzentrationen, die niedriger als ein gewisser Schwellwert waren, konnte Wasser durch die Rhizosphärenschicht fließen, über dieser Konzentration wurde die Schicht wasserundurchlässig während der ersten Minuten bis zu Stunden nach Bewässerung. Wir präsentieren eine analytische Abschätzung der Mucilagekonzentration an der Perkolationsschwelle als Funktion von mittlerer Teilchengröße und Bodenwasserpotential nach Bewässerung. Die Abschätzung wurde an Hand von Experimenten des kapillaren Aufstiegs in Bodensäulen validiert. Wir entwickelten ein effektives Model um zu beschreiben, wir Mucilage die hydraulischen Funktionen des Bodens verändert: (a) Quell- und Trocknungsprozesse von Mucilage resultieren in Nicht-Gleichgewichtsdynamiken zwischen Wassergehalt und Wasserpotential, (b) die Präsenz von Mucilage im Boden reduziert das Wasserpotential bei einem gegebenen Wassergehalt und (c) Mucilage ist viskos und reduziert dadurch die hydraulische Leitfähigkeit des Bodens bei einem gegebenen Wassergehalt. In Experimenten mit Boden-Mucilage-Mischungen testeten wir das Model und wandten es an, um Beobachtungen von früheren Experimenten mit echten Pflanzen zu simulieren, die veränderte hydraulische Dynamiken in der Rhizophäre zeigen. Im Anhang dieser Arbeit sind zwei Studien zur Wärmeausbreitung von Erdkabeln. Hier können hydraulische Dynamiken autreten, die dem radialen Wasserfluss zu einer einzelnen Wurzel ähneln

    Inpact of soil water repellency on water flow and infiltration in fire affected area

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    Nadolazeće klimatske promjene predviđaju izrazitije i duže pojave sušnih razdoblja s povećanjem rizika od požara u Hrvatskoj i značajnom redistribucijom godišnjih oborina. Kao posljedica se očekuje povećanje repelentnosti tla za vodu (RTV). Cilj rada je utvrditi utjecaj požara na hidrauličke karakteristike tla, moguću pojavu hidrofobnosti tla i njezin utjecaj na infiltraciju i tok vode u nesaturiranoj zoni tla. Infiltracijski pokusi s vodom i etanolom na jako opožarenom (A), opožarenom (B) i kontrolnom (C) tlu korišteni su kao osnova za inverzno određivanje hidrauličkih parametara potrebnih za kalibraciju računalnog modela (HYDRUS 2D/3D). Jednogodišnji klimatski scenarij uz primjenu stvarnih meteoroloških podataka je nakon toga simuliran pomoću softverskog programa HYDRUS-1D. Rezultati velikog smanjenja hidrauličke provodljivosti tla (Ks) u područjima A i B ukazuju na RTV. Jednogodišnja simulacija nije pokazala značajan utjecaj RTV na bilancu vode. S druge strane, simulacijom razdoblja intenzivnih oborina, rezultati ukazuju da RTV nastala uslijed dužih sušnih perioda i kratkih intenzivnih oborina povećava mogućnost pojave površinskog otjecanja i smanjenje infiltracijske sposobnosti tla.Expected climate change predictions are suggesting that the occurrence of more pronounced and longer dry periods with an increased fire risk and significant redistribution of annual precipitation may be expected in Croatia. Consequently, an increase of soil water repellency (SWR) is expected. The aim of this thesis is to determine the impact of the fire on the hydraulic characteristics of the soil, the possible appearance of soil hydrophobicity and its influence on infiltration and water flow in the unsaturated soil (vadose) zone. Infiltration experiments with water and ethanol on highly affected (A), affected (B) and control (C) site (non-affected), were used as a basis for the inverse determination of hydraulic parameters required for calibration of a computer model (HYDRUS 2D/3D). The one-year climatic scenario with the application of real meteorological data is then simulated using the HYDRUS-1D software program. The results of a large reduction in soil hydraulic conductivity of the soil (Ks) in sites A and B indicate SWR. Seasonal (one year) simulation did not show a significant impact of SWR on the water balance. On the other hand, by simulating the period of intensive precipitation, the results indicated that SWR caused by longer dry periods and short intensive precipitation increases surface runoff and reduces the infiltration capacity of the soil

    Inpact of soil water repellency on water flow and infiltration in fire affected area

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    Nadolazeće klimatske promjene predviđaju izrazitije i duže pojave sušnih razdoblja s povećanjem rizika od požara u Hrvatskoj i značajnom redistribucijom godišnjih oborina. Kao posljedica se očekuje povećanje repelentnosti tla za vodu (RTV). Cilj rada je utvrditi utjecaj požara na hidrauličke karakteristike tla, moguću pojavu hidrofobnosti tla i njezin utjecaj na infiltraciju i tok vode u nesaturiranoj zoni tla. Infiltracijski pokusi s vodom i etanolom na jako opožarenom (A), opožarenom (B) i kontrolnom (C) tlu korišteni su kao osnova za inverzno određivanje hidrauličkih parametara potrebnih za kalibraciju računalnog modela (HYDRUS 2D/3D). Jednogodišnji klimatski scenarij uz primjenu stvarnih meteoroloških podataka je nakon toga simuliran pomoću softverskog programa HYDRUS-1D. Rezultati velikog smanjenja hidrauličke provodljivosti tla (Ks) u područjima A i B ukazuju na RTV. Jednogodišnja simulacija nije pokazala značajan utjecaj RTV na bilancu vode. S druge strane, simulacijom razdoblja intenzivnih oborina, rezultati ukazuju da RTV nastala uslijed dužih sušnih perioda i kratkih intenzivnih oborina povećava mogućnost pojave površinskog otjecanja i smanjenje infiltracijske sposobnosti tla.Expected climate change predictions are suggesting that the occurrence of more pronounced and longer dry periods with an increased fire risk and significant redistribution of annual precipitation may be expected in Croatia. Consequently, an increase of soil water repellency (SWR) is expected. The aim of this thesis is to determine the impact of the fire on the hydraulic characteristics of the soil, the possible appearance of soil hydrophobicity and its influence on infiltration and water flow in the unsaturated soil (vadose) zone. Infiltration experiments with water and ethanol on highly affected (A), affected (B) and control (C) site (non-affected), were used as a basis for the inverse determination of hydraulic parameters required for calibration of a computer model (HYDRUS 2D/3D). The one-year climatic scenario with the application of real meteorological data is then simulated using the HYDRUS-1D software program. The results of a large reduction in soil hydraulic conductivity of the soil (Ks) in sites A and B indicate SWR. Seasonal (one year) simulation did not show a significant impact of SWR on the water balance. On the other hand, by simulating the period of intensive precipitation, the results indicated that SWR caused by longer dry periods and short intensive precipitation increases surface runoff and reduces the infiltration capacity of the soil
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