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University of Basel (2014)

SOC stock assessment in drylands based on a combined ecohydrology and aerial imagery approach : a case study in the Negev desert, Israel

Hikel, Harald

Titre : SOC stock assessment in drylands based on a combined ecohydrology and aerial imagery approach : a case study in the Negev desert, Israel

Auteur : Hikel, Harald

Université de soutenance : University of Basel

Grade : Doctor of Philosophy (PhD) 2014

Résumé
The global soil system forms the largest pool of terrestrial organic carbon. The inventory of soil organic carbon (SOC) is required for greenhouse gas inventories and carbon mitigation projects. Especially in (semi-) arid ecosystems the size and the dynamics of the SOC pool still lack sufficient investigation. Based on the increasing interest in reliable estimates of SOC stocks in drylands, this thesis aims for the quantification of SOC stocks and patterns in the Northern Highlands of the Negev Desert (Israel) on a regional scale considering SOC spatial heterogeneity at a local scale. The Negev Highlands were chosen as an ideal study site because they represent a characteristic arid environment and several studies regarding lithology, hydrology and vegetation have been carried out there. Because of the high spatial heterogeneity of environmental conditions at local scale in this area, slope sections with different ecohydrologic characteristics (e.g. soil, vegetation) were sampled and SOC stocks were calculated. To identify controlling factors of SOC stocks on rocky desert slopes, soil properties, vegetation coverage, SOC concentrations and stocks were compared between distinctive ecohydrological environments (EHEs). The EHEs are characterized by similar surface conditions (such as geology, rock/soil ratio and soil distribution), water supply and vegetation density. Rock-soil interaction and the relevance of soil volume for storing plant available water and hence the water supply for vegetation coverage determining SOC concentrations and stocks were further examined. Rainfall simulation experiments were therefore conducted to determine the amount of rainfall required to fill the available soil water storage capacity. The design and the selection of the plots aimed specifically at observing infiltration into small soil patches on a micro-scale relevant for prevalent vegetation coverage. Based on this experimental procedure the relationship between environmental properties and SOC concentrations and stocks regarding the distinctive EHEs could be identified at local scale. For the determination of local scale SOC spatial heterogeneity at regional scale an approach towards automated mapping of EHEs was developed. Therefore spatial vegetation pattern indices were calculated based on the analysis of hyperspectral and orthoimage datasets. The indices were then used as variables in a decision tree model for automated mapping of EHEs. For the quantification of SOC stocks at regional scale considering local scale spatial heterogeneity of SOC concentrations and driving processes, a GIS-based image analysis approach was developed using vegetation coverage and EHEs as proxy indicators for SOC concentrations and patterns. The calculated SOC stocks indicate that rocky desert slopes contain a significant amount of SOC of soil-covered areas of 1.54 kg C m-2 , with an average SOC stock over the entire study site of 0.58 kg C m-2 . The calculated SOC-stock for the total area (1km2 ) is 1.19t C ha-1 . Based on the results of this thesis, the understanding of ecohydrological conditions and processes and remote sensing techniques were combined in one methodological approach. This implemented procedure provides the precise estimation of SOC-stocks in arid environments by combining field data and digital image processing approaches.

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Page publiée le 30 décembre 2014, mise à jour le 27 septembre 2017