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of grazing intensity could improve soil functions again under pasture. In order to protect and restore degraded soils from intense grazing, we suggest future land use in Inner Mongolia needs to focus on reducing trampling intensity and animal exclusion. Modeling grazing effects on coupled water and heat fluxes (Chapters 4, 5 and 6) 142 Grazing-induced changes in soil properties were parameterized by the coupled water and heat model HYDRUS-1D (Šimůnek et al., 1998). In addition, we introduced the different root densities and boundary conditions for the different grazing intensities. Especially, three improvements is needed to underline when we calibrated the model. Firstly, we worked with the root growth model to consider dynamics of plant water uptake. We considered it important because models designed to simulate agricultural managements are normally limited to simulate crop growing thus keep root constant, e.g. SWAT (Neitsch et al., 2002). Secondly, interception, which can not be calculated by HYDRUS-1D, was estimated by the model SHAW (Flerchinger and Saxton, 1989) since it might occupy a large component of the water budget in our case. Finally, we partitioned evapotranspiration (ET) based on the field measurements, which was particularly essential for the prediction of plant transpiration since it is only determined by root water extraction function related with potential transpiration in HYDRUS code. The modifications in boundary conditions resulted in a significant improvement of the simulation accuracy. We showed that HYDRUS-1D model is capable to reflect the grazing effects on water and heat budgets, and it can be used for the analysis of land management scenarios. Apart from the inverse model, the Laboratory-derived hydraulic parameter (LDP) model showed the best match between simulated and measured water contents as it accounts for soil structural changes resulted from grazing. This result is consistent with the description by Richard et al. (2001), who distinguished textural and structural fractions for the soil pore space and found that soil compaction mainly affected the structural pore space. Our
Chapter 7 General discussion and conclusions results therefore suggest that the detailed laboratory measurements of soil hydraulic properties from undisturbed soil sampling are necessary to reflect the effect of land managements on water flux. Under the prevailing semi-arid climatic conditions in Inner Mongolia, plant available water plays the most key role for the sustainable development of steppe ecosystems. At this moment, some studies have shown that grazing affects water budget (Bremer et al., 2001). However, to which extent grazing affects evapotranspiration, and how far it is partitioned into transpiration and evaporation is unclear. We proofed that the water budget in Inner Mongolia grassland is significantly influenced by grazing. Although there was no apparent difference in evapotranspiration (ET) among different grazing intensities, the components of ET, i.e. interception, transpiration and evaporation significantly varied with grazing intensity. It is obvious that, compared with the grazed sites, interception and transpiration increased and soil evaporation decreased in the ungrazed sites. In contrast to this, evaporation in the grazed sites simultaneously increased. We deem it important information for judgments of water use efficiency in this region. Currently, although snowmelt or lateral soil water movement on frozen soil layers is recognized as an important part for the seasonal water balance, simulations of snow hydrology and soil freezing and thawing are rarely done due to a lack of suitable models that describe the complex processes during phase changes and limited data availability to parameterize or validate such models (Hansson et al., 2004). Especially, the mutual interactions of water and heat flows in frozen soil are limited to laboratory observation and theoretical analysis, but rarely conducted in field applications. Based on this, an extended freezing code was incorporated into HYDRUS-1D to numerically solve coupled equations governing phase changes between water and ice and heat transport (Hansson et al., 2004). The freezing model was proofed to predict well the soil water and heat fluxes under both unfrozen and frozen conditions. This provided a basis for the studies of soil freezing and thawing behavior. It has been found that soil 143
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SCHRIFTENREIHE Institut für Pflanz
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Aus dem Institut für Pflanzenernä
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I Table of contents I Table of cont
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controlling soil moisture are of pa
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Zusammenfassung Überweidung wird a
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Die Beweidung beieinflusst besonder
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II List of figures Fig. 2.1. Locati
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measured soil moisture in time stab
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III List of tables Table 2.1. Descr
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1.1 Background Chapter 1 Introducti
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Chapter 1 Introduction is also unce
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Chapter 1 Introduction water in spr
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Chapter 1 Introduction requires the
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Chapter 1 Introduction Krümmelbein
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Chapter 2 Spatial variability of so
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Chapter 3 Spatio-temporal variabili
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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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Page 173 and 174: Curriculum Vitae M.Sc. Ying Zhao Of
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