67 research outputs found

    Assessment of Landscape Processes, Forms and Features in the Lake Manyara Region, East African Rift Valley

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    The rift valleys of the East African Rift Systems form two branches (Eastern and Western rift). Within the Eastern rift, there is a southward propagation in the onset of volcanism, and hence rifting that has led to the formation of a narrow graben commonly referred to as the Gregory rift (in Tanzania). The endorheic basin at its southern end where the present saline Lake Manyara was formed. The lakes largest tributary is the Makuyuni River that is providing fresh water from northwest volcanic highlands. Along the Makuyuni River, where first and second tributaries cut deep into the sediments, the landscape is dominated by erosion features. These sediments reveal exposed and outcropping artefacts and fossils, which have been found starting in the 1930s in archaeological and paleontological expeditions. In the close vicinity of Makuyuni town, two hominin bearing sites were discovered in 2008. As few is known about the landscape itself, this study has set its focus on the surrounding landscapes of Makuyuni and its geomorphic implications. Key drivers of landscape development in Northern Tanzania are the tectonics and tectonically induced processes. The thus disrupt drainage networks and analyses thereof can reveal the effects on the morphology of stream longitudinal profiles. These transformations in turn, have an impact on driving river incision, in general on linear erosion phenomena. The triggered rill and gully erosion features will eventually lead to soil loss. Gully erosion is a major threat concerning landscape degradation in semiarid ecosystems, as they remove fertile topsoil and as such prevent agricultural use. The study showed, that most of the gully systems are there for decades and in stable conditions. There are, however, areas of exposed risk for erosion. A detailed examination of soil loss areas, innovative automatic surface runoff detector (SRD) devices have been installed. They measure runoff height and duration. This data contribute to a better understanding of the water cycle as well as to soil functions in semiarid environments. The specific research questions have been considered in five different publications that describe the applied methodologies and results in detail. In order to understand the different geomorphic processes, different methods and scales have been used. Field surveying was an important factor and surface runoff, soil characteristics and erosion phenomena have been sampled and measured. Specifically, this study examined rill and gully erosion features and underwent a detailed mapping around Makuyuni in order to describe and understand the occurring landscape systems. Laboratory procedures involved soil parameter analysing and digital data analysis involved digital elevation model analysis, remote sensing imagery, sophisticated statistical models and in the end a detailed geomorphic map compiling of the greater area. Many studies have focused on partial aspects of geomorphic processes. The frame-work of this doctoral thesis seeks to answer a holistic approach, in order to understand, interpret and discuss related geomorphic processes, their spatial extents and locations. This work contributes to the knowledge of present geomorphic processes and features and the landscape evolution within the Lake Manyara area in Northern Tanzania. The above mentioned methods and analyses may be applicable to similar areas in the African rift.Der große Ostafrikanische Grabenbruch teilt sich im sĂŒdlichen Äthiopien in zwei Hauptsysteme, den östlichen und den westlichen Graben. Im östlichen Graben nehmen die vulkanischen AktivitĂ€ten und daher auch die aktive Grabenbildung nach SĂŒden zu, was zu der heutigen Bildung einer engen Grabenschlucht gefĂŒhrt hat, das sogenannte Gregory Rift in Tansania. An dessen sĂŒdlichem Ende hat sich ein endorheisches Becken gebildet, wo sich heute der flache Salzsee Manyara befindet. Sein grĂ¶ĂŸter Zubringer ist der Fluss Makuyuni, welcher Frischwasser aus den vulkanischen Hochlanden nordwestlich des Beckens mit sich fĂŒhrt. Entlang diesen Flusses haben sich weitere Verzweigungen tief in die Sedimente gegraben; die Landschaft wird von Erosionsformen dominiert. In diesen Sedimenten zeigen sich nun freigelegte Artefakte und Fossilien, welche seit den 1930er Jahren bei archĂ€ologischen wie palĂ€ontologischen Expeditionen entdeckt wurden. In der NĂ€he der Siedlung Makuyuni wurden 2008 zwei Knochenreste von frĂŒhen Hominiden gefunden. Wenig Forschung gibt es ĂŒber die Landschaft selber, die vorliegende Arbeit beschĂ€ftigt sich daher mit der Umgebung Makuyunis und seinen geomorphologischen Eigenschaften. Wesentlich fĂŒr die Formung der Landschaft Nordtansanias sind die tektonischen und tektonisch-getriebenen Prozesse. Die dadurch gestörten Abflussnetzwerke und deren Analysen können die Auswirkungen auf die Morphologie der AbflusslĂ€ngsprofile aufzeigen. Diese VerĂ€nderungen wiederum wirken sich auf die Einschneidungsdynamiken der FlĂŒsse und BĂ€che aus, generell also auf lineare Abflussprozesse. Die so entstehenden Rillen- und Gullyerosionsformen fĂŒhren zu Bodenverlusten. Die Gullyerosion ist eine der grĂ¶ĂŸten Naturgefahren in semiariden Ökosystemen, da sie große Teile des Oberbodens abtragen und so die Landschaft einer agrarischen Nutzung entziehen. Die Arbeit konnte aufzeigen, dass viele der Gullysysteme seit mehreren Jahrzehnten bestehen und stabil sind. Es gibt jedoch Bereiche, die von potentiellen Abtragungsrisiken betroffen sind. Um diese Bodenabtragungen genauer zu untersuchen, wurde mit innovativen OberflĂ€chenabflussdetektoren gearbeitet. Diese messen den OberflĂ€chenabfluss in seiner Höhe und Dauer. Diese Daten tragen zu einem besseren VerstĂ€ndnis des Wasserkreislaufes sowie allgemein zu Bodenfunktionen semiarider Ökosysteme bei. Die jeweiligen Forschungsfragen wurden in fĂŒnf Artikeln abgehandelt, diese beschreiben die angewandten Methoden und Resultate im Detail. Um die verschiedenen geomorphologischen Prozesse zu untersuchen, wurde mit verschiedenen Methoden und verschiedenen Skalen gearbeitet. Die Feldarbeit nahm einen wichtigen Teil ein und es wurden u.a. OberflĂ€chenabfluss, Bodenwerte und Erosionsformen beprobt und vermessen. Im Speziellen wurden auf die Rillen- und Gullyerosion eingegangen sowie auf eine detaillierte Kartierung der Umgebung Makuyunis um die verschiedenen Landschaftssysteme zu beschreiben und zu verstehen. Im Labor wurden die Bodenproben analysiert und mit den digitalen GelĂ€ndemodellen, den Fernerkundungsdaten und statistischen Methoden wurden einzelne Studien durchgefĂŒhrt und am Ende eine geomorphologische Karte des Gebiets erarbeitet. Viele Studien untersuchten Teilbereiche geomorphologischer Prozesse. Im Rahmen dieser Doktorarbeit wurde daher ein ganzheitlicher Ansatz verfolgt, um die geomorphologischen Prozesse, ihre rĂ€umliche Ausdehnung und Verortung zu verstehen, zu interpretieren und die wissenschaftlichen Erkenntnisse als Ganzes zu diskutieren. Diese Arbeit trĂ€gt daher zu neuem Wissen aktueller geomorphologischer Prozesse und Formen sowie der Landschaftsentwicklung als solche in der Umgebung des Manyarasees in Nordtansania bei. Die dabei verwandten Methoden und Analysen sind in Ă€hnlichen Ökosystemen entlang des Ostafrikanischen Grabens anwendbar

    Assessment of Paleo-Landscape Features using Advanced Remote Sensing Techniques, Modelling and GIS Methods in the Lake Manyara Basin, Northern Tanzania

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    In researching the evolution of hominids, the East African Rift System acts as a vital region. The rift valleys enabled some of the most sensational hominid findings to date. Various hypotheses have been developed in the last decades, which try to explain the influence of changes in paleo-climate, paleo-landscape and paleo-environment on hominin evolution in the Quaternary. Additionally, the sediments and the morphology of the East African Rift System provide excellent terrestrial archives for paleo-environmental reconstruction. Lake Manyara is located in an endorheic basin in the eastern arm of the East African Rift System in northern Tanzania. The surroundings of the Lake Manyara are in the focus of paleontological and archaeological investigations. For instance, two hominin bearing sites were found within the catchment of the Makuyuni River, as well as artefacts and fossils are periodically uncovered. The study area, which is located east of the present-day lake, provides an insight into relevant geological and geomorphological drivers of paleo-landscape evolution of the whole region. This thesis aims at contributing to the understanding of landscape evolution in the Lake Manyara region. Compared to other regions in the East African rift system, few landscape evolution studies took place for the Lake Manyara basin. As such, an integrative scientific investigation of the spatial situation of paleo-landscape features and of paleo-lake level fluctuations is missing. The proposed study utilizes state-of-the-art remote sensing based research methods in evaluating the landscape, and in concluding from present-day landforms and processes, how the landscape developed during the Pleistocene and Holocene. In striving to accomplish this goal, this cumulative dissertation comprises eight central research questions, which are introduced in a conceptual framework. The research questions have been considered in seven scientific publications, which describe the applied methodologies and results in detail. The framework of the thesis provides a coherent and detailed interpretation and discussion of the scientific findings. The research questions and outcomes of the analyses are listed below. Key drivers of landscape development in the East African Rift System are tectonic and tectonically induced processes. Drainage network, stream longitudinal profiles and basin analysis based on topographic analyses, as well as lineaments extracted from remote sensing images, were successfully used as methods in identifying tectonic activity and related features in rift areas. The application of a gully erosion model suggests that the gully channel systems in the study area are relatively stable and that they had developed prior to the last significant lake regression. The paleo-landscape and the paleo-environment are closely connected to lake level changes of the paleo-Lake Manyara. Hence, a key question concerns the extent of the Manyara Beds, which are lacustrine deposits that indicate the maximum extent of the paleo-Lake Manyara. A combined analysis, utilizing ASTER multispectral indices and topographic parameters from a digital elevation model, led to the spatial delineation of lacustrine sediments. Their extent indicates a relation to lacustrine sediments in the southern part of the basin, and reveals lacustrine / palustrine deposits further east. A methodological comparison of Support Vector Machines and Boosted Regression Trees, which served as classification methods to identify the lacustrine sediments, exhibited high accuracies for both approaches, with minor advantages for Support Vector Machines. Closely related to the previous research question is the question on the spatial distribution of surface substrates. By incorporating a WorldView-2 scene and Synthetic Aperture Radar data to the previously mentioned datasets, it was possible to distinguish between nine topsoil and lithological target classes in the study area. The surface substrates indicate the underlying lithologies, sediments and soils, as well as soil formation processes. Between the village of Makuyuni and the present-day Lake Manyara, paleo-shorelines and terraces were formed by various paleo-lake levels. Questions arise, at which elevation these features occur and what is the maximum elevation, which was reached. ALOS PALSAR and TerraSAR-X backscatter intensity information provided the possibility of an area-wide mapping of those morphological features. Some radiometric dates exist for stromatolites from a distinct paleo-shoreline level, which support the interpretation of the lake fluctuations. The paleo-shoreline, which was identified with the highest elevation, coincides with the elevation of the lowest possible outlet of the closed Manyara basin. It can be assumed that the paleo-Lake Manyara over-spilled into the neighboring Engaruka and Natron-Magadi basins. The question of the location of sites with a high probability of artefact and/or fossil presence is important for future archaeological and paleontological research. ASTER remote sensing data and topographic indices contributed likewise to the predictive modelling of probabilities of archaeological and paleontological sites in the study area. Generally, paleontological sites are found on a higher elevation, compared to Stone Age sites. In addition, fossil sites seem to be related to stable paleo-landscape features according to this study’s findings. The results of this dissertation provide new insights in the landscape development of the Lake Manyara basin. The scientific findings contribute to the understanding of the landscape evolution for the study area, as well as for the neighboring basins in the East African Rift System. The applied geospatial methodologies can be transferred to other study areas with similar research needs

    Impacts of Climate Variability on Surface Energy and Water Budgets in sub-Saharan Africa

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    According to the IPCC Fifth Assessment Report, climate change will exacerbate current climate and non-climate stressors on agricultural systems in sub-Saharan Africa. This will adversely impact food security and the wellbeing of communities. Small-scale farmers grow more than 90 percent of the food produced in the region and many households depend on productive local growing conditions to support for their families. A better understanding of recent and near future climate constraints is important for identifying future food security risks and locally-appropriate adaptation strategies.This dissertation research examines impacts of weather and climate on vegetation productivity in geographically diverse areas of east Africa and the semi-arid Sahel. The focus of this research is how surface energy and water budgets respond to variations in rainfall and temperature. It asks the following questions: Where will warmer temperature pose a hazard to rainfed agriculture in the Sahel in the next 20 years? What environment and weather conditions led to above average surface temperature during the recent decade in east Africa? How have declines in rainfall since the 1980s impacted vegetation productivity and hydrology in Tanzania? The research incorporates a variety of earth observation data, including historical records from in situ, model-derived, and satellite-observed sources and projections from global climate models. A major contribution is the identification of specific areas, mainly in semi-arid climate zones, where increases in temperature and decreases to rainfall have large negative impacts on vegetation productivity. The research also presents new methods for evaluating land-atmosphere interactions in the context of hazards to vegetation

    Pinpointing areas of increased soil erosion risk following land cover change in the Lake Manyara catchment, Tanzania

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    publisher: Elsevier articletitle: Pinpointing areas of increased soil erosion risk following land cover change in the Lake Manyara catchment, Tanzania journaltitle: International Journal of Applied Earth Observation and Geoinformation articlelink: https://doi.org/10.1016/j.jag.2018.05.008 content_type: article copyright: © 2018 Elsevier B.V. All rights reserved

    Surface water – groundwater interactions: A case of a shallow semi-closed lake catchment in northern Tanzania

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    A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Water Resources Engineering of the Nelson Mandela African Institution of Science and TechnologyConjunctive use of surface water and groundwater is rapidly growing in many developing countries as an adaptation strategy to climate variability and change. However, the interactions between the groundwater and the surface water systems are not adequately understood, especially among the East African rift valley lakes, where data paucity has limited studies and reporting on the spatial influence of catchment heterogeneity. In its humble contribution to sustainable water development, this study aimed to present a platform for understanding the influence of climatic variation and anthropogenic activities on surface water–groundwater interactions. To be relevant locally, Lake Babati, a freshwater lake in Northern Tanzania that provides the community with fish, freshwater, and a habit for hippopotamus, was studied. The study applied hydrological simulation, grey relational analysis, and stepwise regression analysis to model the hydrological behaviour of the lake. Further, it used hydrogeochemistry and environmental isotopes to identify groundwater fluxes and draw the conceptual understanding of surface water – groundwater interaction and applied topography-based indices to spatially map groundwater potentials within the catchment. The results showed that Lake Babati level is significantly declining (p-value < 0.01) at a rate of 25 mm per annum. The lake level decline could not be explained by climatic variability since the decline occurred when both evaporation and rainfall showed no significant changes either seasonally or annually. Instead, the consistent decline of the lake level in all seasons could be due to the expansion of the spillway, which effectively lowered the lake reservoir level and increased the lake outflow in rainy seasons. The hydro-geochemistry and isotopes data showed that the lake water and groundwater interact and are in hydraulic connections. Further, using Height Above Nearest Drainage based and Topography Wetness Index based methods, the study developed two groundwater potential maps to predict groundwater spatial variability and guide groundwater prospecting efforts and subsequent development. Given that Lake Babati is in a hydraulic connection with the groundwater, its consistent decline will likely impact the groundwater system. Similarly, abstracting groundwater at unsustainable rates could lower the lake levels further. Therefore, integrated water resources management is required for sustainable water resources development and management in the catchment. Mandatory and continuous monitoring of the water resources (groundwater levels, river flows, and lake levels) is recommended to generate quality in situ data for future studies

    Land Use and Environmental Gradients Influence on Riparian Woody Plant Diversity and Structure in Lake Manyara Watershed Ecosystem, Tanzania

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    This research article was published in Open Journal of Ecology, Volume 13, 2023.Riparian vegetations are important in supporting ecological connectivity between aquatic and terrestrial ecosystems. The structure and species composition of riparian woody plants have been subjected to multiple forces with varying degree of influences. This study examined the influence of land use and environmental gradient to the structure and composition of the riparian woody plants in northern Tanzania. A total of 270 plots were surveyed for woody plant species in the riparian ecosystems and later analysed to determine the influence of land use categories (homegarden, crop field, woodlot, open canopy forest, and closed canopy forest) and environmental variables (temperature, precipitation, elevation and slope) to the species richness, abundance, and stand parameters. Basal area was higher in woodlots, homegardens and crop fields than in the open and closed canopy forests; and as expected the reverse was true for the number of stocking density. Correlation among stand parameters with environmental variables varied significantly. Species richness and species abundance were negatively correlated to precipitation, temperature and elevation, while stocking density and basal area were positively correlated to precipitation. The study recommends continual retentions of trees on farm, further promoting of agroforestry interventions and sustainable utilization of woody plants in open and close canopy forests

    Hydrologic responses to climate and land use/cover changes in world heritage site of Ngorongoro conservation area and surrounding catchments, northern Tanzania

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    A Dissertation submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Hydrology and Water Resources Engineering of the Nelson Mandela African Institution of Science and TechnologyIn Tanzania, various studies have analyzed the impact of climate and land use/cover changes on water resources. However, information on the interactions between climate and land use/cover change, temporal and spatial variability of hydrological components and water quality at the local scale is insufficient. The objective of this study was to evaluate the hydrological response to climate and land use/cover changes in Ngorongoro Conservation Area (NCA) and surroundings. The study performed climate change analysis using outputs from a multi-model ensemble of Regional Climate Models (RCMs) and statistically downscaled Global Climate Models (GCMs). The CA–Markov model applied to project Land use/cover for the future 2025 and 2035. This study further used the Soil Water Assessment Tool (SWAT) modelling approaches to analyse the hydrological responses and HYDRUS 1D to determine the change in Groundwater quality due to climate and land use/cover changes. The analysis of climate change between historical period (1982-2011) and future period (2021-2050) indicated an increase in the mean annual rainfall and temperature, seasonal rainfall except June to September (JJAS) season which showed a decreasing trend. Spatially, rainfall and temperatures would increase over the entire area. The projected Land use/cover change for the period 2025 to 2035 compared to the baseline 2016, showed a reduction in bushland, forest, water, and woodland, but an intensification in cultivated land, grassland, bare land, and the built-up area. The surface runoff, evapotranspiration, lateral flow, and water yield would significantly increase in the future, while groundwater would decrease under combined climate and land use/cover change. It is predicted that two anions (Cl− and PO4 −3 ) and two cations (Na+ and K+ ) would exceed the permissible limits for the drinking water set by the World Health organisation (WHO) and Tanzania Bureau of Standards (TBS), from 2036 to 2050. Changes in groundwater quality due to major cations and anions is significantly correlated to evapotranspiration and temperature with Pearson correlation (r) between 0.35 and 0.85. Furthermore, correlate to the changes in all land use/ cover types with Pearson correlation (r) between 0.56 and 0.96. The results obtained provide further insight into future water resources management planning and adaptation strategi

    Soil erosion and sediment transport in Tanzania: Part II – sedimentological evidence of phased land degradation

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    Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality

    Using the water balance approach to understand pool dynamics along non-perennial rivers in the semi-arid areas of South Africa

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    The Touws River in the Klein Karoo region of South Africa Study focus: This study sought to improve the understanding of pool dynamics along non-perennial rivers (NPRs) by utilising the water balance approach to assess the water fluxes that influence pool dynamics in the Touws River. The water balance model made use of various in-situ and satellite-derived data. New hydrological insights: The analysis of the water losses from the pool showed that most of the water was lost through evaporation. The interaction between the pool and groundwater is dependent on the water levels, as the pool loses water to the subsurface up to a certain depth then it starts gaining. When the Wolverfontein 2 pool is full, it can retained water for approximately 258 days without having a surface water inflow
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