The Okavango river flows from southern Angola, through the Kavango region of Namibia and into the Okavango Delta in Botswana. The recent peace in Angola hopefully marks the end of the intense suffering that the peoples of the river basin have endured, and the beginning of sustainable decision-making in the area. Informed decision-making however requires knowledge; and there is a need for, and a lack of knowledge regarding basin-wide land cover (LC) changes, and their causes, during the Angolan civil war in the basin. Furthermore, there is a need for, and a lack of knowledge on how expanding large-scale agriculture and urban growth along the Angola-Namibia border affects the water quality of the river. The aim of this study was therefore to develop a remote sensing method applicable to the basin (with scant ground-truth data availability) to carry out a systematic historic study of LC changes during the Angolan civil war, to apply the method to the basin, to relate these changes to major societal trends in the region, and to analyse potential impacts of expanding large-scale agriculture and urban growth on the water quality of the river along the Angola-Namibia border. A range of remote sensing methods to study historic LC changes in the basin were tried and evaluated against reference data collected during a field visit in Namibia in October 2005. Eventually, two methods were selected and applied to pre-processed Landsat MSS and ETM+ satellite image mosaics of 1973 and 2001 respectively: 1. a combined unsupervised classification and pattern-recognition change detection method providing quantified and geographically distributed binary LC class change trajectory information and, 2. an NDVI (Normalised Difference Vegetation Index) change detection method providing quantified and geographically distributed continuous information on degrees of change in vegetation vigour. In addition, available documents and people initiated in the basin conditions were consulted in the pursuit of discerning major societal trends that the basin had undergone during the Angolan civil war. Finally, concentrations of nutrients (total phosphorous & total nitrogen), bacteria (faecal coliforms & faecal streptococci), conductivity, total dissolved solids, dissolved oxygen, pH, temperature and Secchi depth were sampled at 11 locations upstream and downstream of large-scale agricultural facilities and an urban area during the aforementioned field visit. The nature, extent and geographical distribution of LC changes in the study area during the Angolan civil war were determined. The study area (150 922 km2) was the Angolan and Namibian parts of the basin. The results indicate that the vegetation vigour is dynamic and has decreased overall in the area, perhaps connected with precipitation differences between the years. However while the vigour decreased in the northwest, it increased in the northeast, and on more local scales the pattern was often more complex. With respect to migration out of Angola into Namibia, the LC changes followed expectations of more intense use in Namibia close to the border (0-5 km), but not at some distance (10-20 km), particularly east of Rundu. With respect to urbanisation, expectations of increased human impact locally were observed in e.g. Rundu, Menongue and Cuito Cuanavale. Road deterioration was also observed with Angolan urbanisation but some infrastructures appeared less damaged by the war. Some villages (e.g. Savitangaiala de Môma) seem to have been abandoned during the war so that the vegetation could regenerate, which was expected. But other villages (e.g. Techipeio) have not undergone the same vegetation regeneration suggesting they were not abandoned. The areal extent of large-scale agriculture increased 59% (26 km2) during the war, perhaps as a consequence of population growth. But the expansion was not nearly at par with the population growth of the Kavango region (320%), suggesting that a smaller proportion of the population relied on the large-scale agriculture for their subsistence in 2001 compared with 1973. No significant impacts were found from the large-scale agriculture and urbanisation on the water quality during the dry season of 2005. Total phosphorous concentrations (with range: 0.067-0.095 mg l-1) did vary significantly between locations (p=0.013) but locations upstream and downstream of large-scale agricultural facilities were not significantly different (p=0.5444). Neither did faecal coliforms (range: 23-63 counts per 100ml) nor faecal streptococci (range: 8-33 counts per 100ml) vary significantly between locations (p=0.332 and p=0.354 respectively). Thus the impact of Rundu and the extensive livestock farming along the border were not significant at this time. The Cuito river on the other hand significantly decreased both the conductivity (range: 27.2-49.7 μS cm-1, p<0.0001) and the total dissolved solid concentration (range: 12.7-23.4 mg l-1, p<0.0001) of the mainstream of the Okavango during the dry season. Land cover changes during the Angolan civil war, contributing causes and effects on water quality were studied in this research effort. Many of the obtained results can be used directly or with further application as a knowledge base for sustainable decision-making and management in the basin. Wisely used by institutions charged with that objective, the information can contribute to sustainable development and the ending of suffering and poverty for the benefit of the peoples of the Okavango and beyond.

Cette étude utilise une approche multidisciplinaire à dominante géochimique, avec plusieurs objectifs : 1) mieux comprendre les processus géochimiques au cours du cycle de genèse des formations sédimentaires (érosion-transport-accumulation) pour des stages précoces de l'évolution d'un bassin de rift : 2) reconstruire les environnements caractérisant ces deux régions du Rift Est-africain au cours du Pélistocène et de l'Holocène et 3) définir des critères sédimentologiques et géochimiques permettant de discriminer l'activité tectonique et les changements climatiques au cours de l'évolution de ces deux bassins du rift. Les deux bassins considérés comme illustrant deux stages précoces successifs de l'ouverture d'un bassin de rift, sont : 1) le Bassin de Makgadikgadi-Okavango-Zambeze (MOZ), situé dans la région nord-ouest du Botswana et 2) le Bassin de Mpulungu, qui constitue l'extrémité sud-est du Bassin du Lac Tanganyika (Tanzanie et Zambie). L'étude géochimique des sédiments et des eaux du Bassin de l'Okavango a révélé la présence anormale d'arsenic dans les eaux souterraines du delta résultant de la dissolution sous conditions réductrices dans les sédiments. La présence de l'arsenic dans les sédiments est liée aux argiles riches en matière organique déposés dans les conditions lacustres résultant de périodes à pluviométrie plus importante qu'aujourd'hui et du barrage des écoulements de la rivière de l'Okavango apr la faille de Thamalakane. Les données géochimiques ont été utilisées comme marqueur deschangements du climat dans le bassin de Mpulungu. Les sédiments révèlent une excursion remarquable qui coïncide avec le Younger Dryas. Cet événement environnemental apparaît comme le plus important dans la région sud du lac Tanganyika pour la période 23-3 ka, caractérisée par un apport de matériel altéré dans le bassin, suite à une modification importante du couvert végétal.

<p>This thesis presents models applicable for aquatic ecosystems. Geographical Information Systems (GIS) form an important part of the thesis. The dynamic mass balance models focus on nutrient fluxes, biotic/abiotic interactions and operate on different temporal and spatial scales (site, local, regional and international). The relevance and role of scale in mass balance modelling is a focal point of the thesis.</p><p>A mesocosm experiment was used to construct a model to estimate the nutrient load of phosphorus and nitrogen from net cage fish farming (i.e., the site scale). The model was used to estimate what feeding conditions that are required for a sustainable aquaculture scenario, i.e., a zero nutrient load situation (a linkage between the site scale and the regional scale). </p><p>A dynamic model was constructed for suspended particulate matter (SPM) and sedimentation in coastal areas (i.e., the local scale) with different morphometric characteristics and distances to the Sea. The results demonstrate that the conditions in the Sea (the regional and international scale) are of fundamental importance, also for the most enclosed coastal areas.</p><p>A foodweb model for lakes was transformed and recalibrated for Baltic Sea conditions (i.e., the international scale). The model also includes a mass balance model for phosphorus and accounts for key environmental factors that regulate the presuppositions for production and biomasses of key functional groups of organisms. The potential use of the new model for setting fish quotas of cod was examined.</p><p>For the intermittent (i.e., regional) scale, topographically complex areas can be difficult to define and model. Therefore, an attempt was made to construct a waterscape subbasin identification program (WASUBI). The method was tested for the Finnish Archipelago Sea and the Okavango Delta in Botswana. A comparison to results from a semi-random delineation method showed that more enclosed basins was created with the WASUBI method.</p>

This thesis presents models applicable for aquatic ecosystems. Geographical Information Systems (GIS) form an important part of the thesis. The dynamic mass balance models focus on nutrient fluxes, biotic/abiotic interactions and operate on different temporal and spatial scales (site, local, regional and international). The relevance and role of scale in mass balance modelling is a focal point of the thesis. A mesocosm experiment was used to construct a model to estimate the nutrient load of phosphorus and nitrogen from net cage fish farming (i.e., the site scale). The model was used to estimate what feeding conditions that are required for a sustainable aquaculture scenario, i.e., a zero nutrient load situation (a linkage between the site scale and the regional scale). A dynamic model was constructed for suspended particulate matter (SPM) and sedimentation in coastal areas (i.e., the local scale) with different morphometric characteristics and distances to the Sea. The results demonstrate that the conditions in the Sea (the regional and international scale) are of fundamental importance, also for the most enclosed coastal areas. A foodweb model for lakes was transformed and recalibrated for Baltic Sea conditions (i.e., the international scale). The model also includes a mass balance model for phosphorus and accounts for key environmental factors that regulate the presuppositions for production and biomasses of key functional groups of organisms. The potential use of the new model for setting fish quotas of cod was examined. For the intermittent (i.e., regional) scale, topographically complex areas can be difficult to define and model. Therefore, an attempt was made to construct a waterscape subbasin identification program (WASUBI). The method was tested for the Finnish Archipelago Sea and the Okavango Delta in Botswana. A comparison to results from a semi-random delineation method showed that more enclosed basins was created with the WASUBI method.

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Intraguild competition and predation have been recognised as important ecological factors influencing the population dynamics of carnivores. The effects of these interactions are often asymmetrical due to a size-related dominancy hierarchy. However, it has been suggested that competitively subordinate carnivores can minimise the costs of predation and competition through spatial and temporal avoidance. Here I investigate the ecological and behavioural mechanisms by which cheetahs (Acinonyx jubatus) coexist with competitively stronger lions (Panthera leo) and spotted hyaenas (Crocuta crocuta). Fieldwork was carried out in the Okavango Delta, northern Botswana, between October 2008 and August 2011. A total of 20 Global Positioning System (GPS) radio-collars were fitted on all known cheetahs (n=6), lion prides (n=5) and spotted hyaena clans (n=6) in the study area (approx. 3 000 km²). Pre-programmed radio-collars recorded locations and activity continuously for each individual and these data were complemented with direct behavioural observations. Cheetah data were analysed with respect to the temporal and spatial likelihood of encountering lions and spotted hyaenas. Results suggest that the response to the risks posed by other predators is species-specific, habitat-specific and dependent on the immediacy of the risk. Resource partitioning was not the main mechanism for coexistence as cheetahs overlapped extensively with lions and spotted hyaenas in time, space and habitat use. Instead, cheetahs adjusted their spatial distribution in response to immediate risks or adapted their habitat use depending on their vulnerability (e.g. behaviours such as feeding or with differing levels of moonlight at night). In general, cheetah temporal and spatial distribution is a hierarchal process, firstly driven by resource acquisition and thereafter fine-tuned by predator avoidance. In addition, habitat heterogeneity seemed to be key in facilitating coexistence. Understanding the behavioural mechanisms that interacting apex predators adopt to regulate these negative interactions could be crucial to carnivore conservation, especially as human-related habitat loss is forcing species into ever smaller areas.