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1.2 State of the art Given the vital importance for the production of live stock and the environmental changes, it is crucial to have a thorough understanding of the mechanisms that maintain or change the ecosystem in response to the changes of land management. In order to develop sustainable management strategies, it is essential to investigate the processes emerging from pasture practices. Since many of the rangelands are located in arid or semi-arid areas, water is one of the key variables determining the fate of ecosystem situated in such regions. Therefore, the understanding of the hydrologic processes is critically important (Sugita et al., 2007). Especially, the identification and prediction of soil moisture patterns (spatio-temporal organization) at different scales are necessary to understand underlying processes controlling the hydrological response of a region or even catchment (Grayson et al., 2002; Lin et al., 2006). It has been accepted that environmental variables that are used to evaluate an ecosystem, e.g. soil properties, are spatial dependent (Goovaerts, 1998). The spatial dependency is commonly characterized and quantified by geostatistical methods such as autocorrelation and variogram analysis. Furthermore, multivariate geostatistics can deal with multivariate spatial data to classify the correlation of regionalization variables and to define scale-dependent relationships (Goovaerts, 1992). This is needed to extrapolate or interpolate variables from different spatial scales when employing either upscaling or downscaling procedures (Western et al., 1999). For instance, when matter fluxes on various scales are investigated, it could be very useful to upscale water flux with the aid of physically-based hydrological models from plot to catena and finally to a regional scale (Fig. 2). Furthermore, it is possible to select monitoring site(s) representing the true field mean conditions in terms of temporal stability concept. If this is assumed, it is suitable to turn to the detailed scenario analysis on the plot scale to evaluate effects of grazing on hydraulic process after investigating a general natural process in the regional or field scale. In addition, a hydrological model normally selected the modeled location without a prior analysis so that the modeled result 2
Chapter 1 Introduction is also uncertain. Thus, the hydraulic model, linked with representative of monitoring locations, should be more valuable to get a comparable conclusion considering spatial variability. year month day hour aggregate soil moisture regime grazing effect aggregation 1D- modeling soil moisture water flux scaling flow separation HYDRUS model 2D- modeling water budget computing hydrograph rainfall etc. plot catena catchment Fig. 1.2. Methodology to understand and quantify the hydrological processes at different spatio-temporal scales (personal communications with Prof H. Zepp, Ruhr-University Bochum, Germany; 2004). Land management is reported to influence soil hydraulic and thermal properties by altering soil and plant functions (Flerchinger et al., 2003). In pasture areas, soil mechanical disturbances due to animal trampling, interlinked with hydrological changes, often have detrimental effects on soil properties. Particularly in the topsoil, soil deformation is characterized by a decrease of pore volume and an altered pore size distribution, which both affect water and air conductivity (Willat and Pullar, 1983; Krümmelbein et al., 2006), and soil water retention characteristics (Martinez and Zinck, 2004; Kutilek et al., 2006). These disturbances of soil structure further decrease water infiltrability and increase surface runoff. This will not only cause soil erosion by water and nutrient 3
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Chapter 3 Factors controlling spati
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Chapter 4 Temporal stability of soi
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Y orientation Chapter 4 Temporal st
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MRD(%) MRD(%) 100 80 60 40 20 0 -20
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Soil water content (%) 40 30 20 10
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Chapter 5 Modeling Grazing Effects
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Chapter 6 Modeling of Coupled Water
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Chapter 7 General discussion and co
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References Chapter 7 General discus
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8. ACKNOWLEDGMENTS Firstly I would
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Curriculum Vitae M.Sc. Ying Zhao Of
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Schriftenreihe des Instituts Neuere
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