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depletion, but also decrease the water availability and further increase soil erosion by wind. Thus, it is essential to quantify and predict management effects on soil properties to assess their consequences on plant production and the environment. Many studies have focused on the effects of land management on soil properties (Green et al., 2003). However, few studies have dealt with the consequences of these practices on water and heat fluxes (Chung and Horton, 1987; Peth and Horn 2006; Ndiaye et al., 2007). Especially, considering the stress-dependent changes of the environment, an adequate account of water flow processes and its spatial variability based on hydrological models is still lacking due to the complexity of the soil system (Ndiaye et al., 2007), although there are widely applicable hydrological models like SHAW (Flerchinger and Saxton, 1989), HYDRUS (Šimůnek et al., 1998) and SWAT (Neitsch et al., 2002). Especially, considering the amount of plant available water as one of the most limiting factors for sustainable grassland development, the effects of grazing on water-related mechanisms and water budgets is urgently needed to be understood in our studied area (Chen and Wang, 2000). Some studies have shown that grazing increases evaporation but decreases transpiration because of increasing bare ground area and reducing amount of biomass. Therefore, the heavily grazed sites are more susceptible to drought, and prone to being degraded due to the reduction of available soil water (Snyman, 2005; Zhang et al., 2005). However, to which extent grazing affects evapotranspiration, and how far it is partitioned into transpiration and evaporation remains unclear (Leenhardt et al., 1995). Furthermore, although water interception by the canopy and plant residues might occupy large volumes of water in steppe ecosystems, it normally is neglected or mixed with soil evaporation. Moreover, it is widely recognized that the movement of water and heat are closely coupled and strongly affected by each other, but their mutual interactions are rarely considered in practical applications. Frozen soil normally reduces infiltration capacity dramatically due to blocking of pores by the formation of ice lenses. As a result, lateral flow and snow melt may release huge quantities of 4
Chapter 1 Introduction water in spring and early summer, and cause surface runoff (Lewkowicz and Kokelj, 2002; Bayard et al., 2005). Especially, in cold and arid regions like in our studied area, quantification of the freezing and thawing effects on the water availability, runoff generation and groundwater recharges are essential. Currently, the model of snow hydrology and soil freezing and thawing processes is comparable lacking not only for model complexity but also for lacking data to fully parameterize or validate the model. 1.3 Objectives In the light of the absence of interdisciplinary studies of rangelands in northeastern Asia, a project called MAGIM (Matter fluxes in grasslands of Inner Mongolia as influenced by stocking rate) has been funded by DFG (Deutsche Forschungsgemeinschaft) for 3 years (2004-2006; website: http://www.magim.net). The principal objective of MAGIM is to understand how grazing of steppe ecosystem feedbacks on water, nitrogen and carbon fluxes on site and regional scales. This comprehensive task requires research on various scales involving detailed laboratory and field experiments as well as concurrent model development and application. Under the framework of the project MAGIM, our objectives are to explore soil physical, hydrological and ecological processes by combining detailed field and laboratory measurements with process oriented modeling techniques to evaluate the influence of rangeland management (i.e. ungrazed since 1979=UG 79, ungrazed since 1999=UG 99, winter grazed=WG, continuously grazed=CG and heavily grazed=HG; Fig. 1) on water and heat fluxes in particular. The study presented here is focusing on following objectives: Chapter 2: “Spatial variability of soil properties affected by grazing intensity in Inner Mongolia grassland” Although many investigations have been dealt with the productivity and stability of this steppe ecosystem, conclusions aiming at the development of sustainable management strategies are hard to be derived from those studies. It is reasoned 5
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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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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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