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http://www.magim.com) are used to parameterize the model HYDRUS-1D. Conversely, modeling results are compared with in situ soil water and temperature measurements to verify the model parameterization. The objectives of this study are: (i) to quantify the grazing effects on water and heat fluxes by a Richards’ based hydraulic model, and (ii) to identify water use mechanisms in a typical Inner Mongolia grassland ecosystem. Study Site Descriptions 88 MATERIALS AND METHODS Experimental Site and Measurements This study was performed on long-term experimental sites of the Inner Mongolia Grassland Ecosystem Research Station (IMGERS; 43 o 37′50′′N, 116 o 42′18′′E) situated in the Xilin River catchment (3650 km 2 ). The vegetation is characterized by the perennial rhizome grass Leymus chinensis and bunch grass Stipa grandis, respectively. Soils are classified as Mollisols according to USDA (1999). In the last two decades, annual mean air temperature was 0.7°C and precipitation was 343 mm, of which more than 85% fell during the growing period. Although rainfall season occurs during the vegetation period, plant water uptake is limited because of strong seasonal and inter-annual rainfall fluctuations (Chen and Wang, 2000). Four sites with different grazing intensities were investigated. Two sites were ungrazed since 1979 (UG 79, 24 ha) and 1999 (UG 99, 35 ha). The other two sites were grazed: one was grazed only during winter time with 0.5 sheep units (ewe and lamb) ha -1 yr -1 (WG, 40 ha) and the other was heavily grazed with 2 sheep units ha -1 yr -1 (HG, 100 ha) during the whole year. Before fencing, all sites were moderately grazed. Field and Laboratory Measurements Soil moisture and temperature were measured at 30-min intervals using horizontally inserted Theta-probes (Type ML2x, Delta-T Devices, Cambridge, UK) and Platinum ground temperature probes (Pt-100), respectively. Theta-probes were calibrated soil specific and installed in three depths at 5, 20, and 40 cm. Soil temperature was measured in five depths at 2, 8, 20, 40, and 100 cm. At
Chapter 5 Modeling Grazing Effects on Coupled Water and Heat Fluxes in Inner Mongolia Grassland each site three replicate profiles were installed and connected to one solar powered automatic data-logger. Moreover, an in situ micrometeorological station was installed to record precipitation and other variables necessary to estimate the reference evapotranspiration (ET) from the FAO Penman-Monteith equation (Allen et al., 1998). Some missing data, especially in 2004 when our experiments began, were filled with data from the weather station of IMGERS (3 km away) and calibrated to the local conditions. To calibrate the modeled boundary condition, weighing mini-lysimeter experiments were conducted to partition soil evaporation (E) from ET. Lysimeters were designed by inserting PVC tubes (20.0 cm long, 5.4 cm diameter) into the ground and sealing them at the bottom. At each site, three replicates were installed at selected locations for both representative grass cover and bare soil surface, respectively. Weighing was conducted bihourly by an electronic balance where the corresponding water loss is referred to as ET for grass-covered ground and as E for bare ground, respectively. The difference between ET and E is consequently calculated considering the vegetal coverage and referred to as transpiration (Tp). Crop parameters, such as vegetation coverage, leaf area index (LAI), and plant height, were taken from vegetation measurements (Gao, 2007). In addition, also the residue coverage and weight were recorded. To determine the root length density, root samples were taken with a soil root auger and soil cores were separated into five depths of 0-10, 10-20, 20-50, 50-70, and 70-100 cm. Undisturbed soil samples were taken from four layers at 4-8, 18-22, 30-34, and 40-44 cm depths (Table 1). Soil texture was determined by pipette method, and total C-content was measured coulometrically. Water retention functions were determined with a ceramic pressure plate assembly by stepwise desaturating initially saturated samples at equilibrium matric potentials of -1, -3, -6, -15, -30, and -1500 kPa. Soil bulk density was determined after oven-drying. Finally, saturated hydraulic conductivity (Ks) was determined with a falling head permeameter (Hartge and Horn, 1999). Water and heat flow equations Numerical Modeling 89
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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 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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