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Universität für Bodenkultur Wien (2016)

Assessment of land degradation processes in the northwestern Ethiopian Highlands

Addis, Hailu Kendie

Titre : Assessment of land degradation processes in the northwestern Ethiopian Highlands

Auteur : Addis, Hailu Kendie

Université de soutenance : Universität für Bodenkultur Wien

Grade : Dr. nat. techn. 2016

Résumé
Soil erosion in the northwestern Amhara region, Ethiopia has been a subject of anxiety, resulting in a major environmental threat to the sustainability and productive capacity of agricultural areas. In the present thesis, selected soil properties, hydrological and sediment dynamics were assessed for a watershed, while predicting the spatial distribution of soil properties was also done. The 53.7 km2 Gumara-Maksegnit watershed was divided into a 500 m by 500 m grid to sample bulk density ([rho]d), pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP) and texture of topsoil (roughly 10 to 25 cm depth). Such properties were investigated with respect to the two main land uses (forest and agriculture) and three different slope steepness classes, 0-10 (%), 10-30 (%), >30 (%). The result indicated higher SOC, TN, silt and sand content in forest soils compared to agricultural soils, while [rho]d is lower in the forest soil. In the second part, the performance of ordinary kriging (OK), inverse distance weighting (IDW) and radial basis functions (RBF) for predicting the spatial distribution of soil texture, pH, soil organic carbon (SOC) and available phosphorus (AP) were done. The performance of each interpolation method was assessed quantitatively in terms of Nash-Sutcliffe efficiency (E), coefficient of determination (R2) and index of agreement (d). The interpolated maps generated based on the highest value of E displayed OK was best performed for SOC and sand. RBF was most suitable for mapping of AP and clay, while IDW gave better result when applied to pH. In the third part, the Soil and Water Assessment Tool (SWAT) model was used to model hydrology and sediment dynamics of the watershed. The resulting Nash-Sutcliffe efficiency (NSE) for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period, suggesting satisfactory model performance.

Mots clés : Agricultural watershed / erosion / Ethiopian Highlands / interpolation / landuse / radial basis functions / semivariogram / slope steepness / soil and water conservation / soil properties / watershed hydrology — Landwirtschaftliches Einzugsgebiet / Äthiopisches Hochland / Interpolation / Landnutzung / Radial Bias Functions / Semivariogramm / Geländeneigung / Boden- und Wasserschutz / Bodeneigenschaften / Einzugsgebietshydrologie

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