Browsing by Author "Eckardt, Frank"

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    Open Access
    A pluralistic, socio-ecological approach to understand the long-term impact of mountain conservation: a counterfactual and place-based assessment of social, ecological and hydrological change in the Groot Winterhoek Mountains of the Cape Floristic Region
    (2018) Holden, Petra Brigitte; Hoffman, Timm; Eckardt, Frank; New, Mark; Smit, Julian; Visser, Martine; Ziervogel, Gina
    The problem: For protected areas to remain relevant, we need to understand their impact on a wide set of conservation objectives and environmental outcomes. We also need to evaluate how this influence relates to the socio-ecological environment within which they occur. This is a complex endeavour requiring a pluralistic approach, which draws on a wide range of interdisciplinary fields. Research question: This thesis addresses the following question: What effects do mountain protected areas have on ecosystem services over time and how does this influence relate to broader socio-economic and ecological drivers of landscape change? Aim and objectives: I use a pluralistic, socio-ecological framing to assess the impact of ~40 years of mountain protection, drawing on comparisons of ~30 and ~40 years before and after protection respectively, with an adjacent area of similar terrain informing scenarios of counterfactual conditions. I also investigate what types of values (economic and intrinsic) are important when determining the impact of mountain protected areas. Thesis approach and methods: I operationalise the concepts of socio-ecological systems, ecosystem services, land use transitions and counterfactuals to investigate socio-ecological change and how it relates to protected area impact in the Groot Winterhoek, a mountain catchment in the south-western Cape of South Africa. This mountain catchment is important for regional water supplies for agricultural and domestic uses and falls in the Cape Floristic Region, a global biodiversity hotspot. It is comprised of privately owned mountain wildlands and a wilderness-protected area, known as the Groot Winterhoek Wilderness Area, established in 1978 (gazetted in 1985) which forms part of the Cape Floristic Region World Heritage Site. I combine methods from social science, ecology, environmental geography, geomatics and hydrology to understand the history of land use and cover (land use/cover) and associated ecosystem service trade-offs, how they are perceived by landowners as well as their wider impact on the region. Specifically, I assess the impact of protection on land use/cover, vegetation, fire and water flows over the last ~50 years, by comparing and contextualising results of change within the protected area to alternative scenarios of “no protection” (the counterfactual conditions). Vegetation and land use/cover change inside the protected area were determined respectively using 72 repeat terrestrial photographs and vegetation surveys, and an analysis of orthorectified aerial imagery. Methods used to construct the counterfactual scenarios of mechanisms (e.g. changes in land use/cover) that would likely drive vegetation changes inside the protected area included: i) 60 repeat surveys and in-depth interviews with landowners adjacent or proximal to the protected area owning unprotected land of similar terrain to the protected area; and ii) land use/cover change analysis of orthorectified aerial imagery of adjacent unprotected land of similar terrain before and after protected area establishment. 4 This latter information was used to understand the role of the protected area in driving vegetation changes inside the protected area. Social, biophysical and remote sensing results were directly used to parameterise land use/cover components of a hydrological model to determine the influence of protection on water flows. Specifically, water flows were simulated for the current state of the environment inside the protected area as well as for several counterfactual scenarios i.e. the alternative land use/cover scenarios of “no protection”. These counterfactual scenarios included land use/cover at two-time steps of ~30 and ~8 years before protection and one-time step ~40 years after protection both inside and outside the protected area. Results: Long-term change in ecosystem service use outside the protected area on privately owned land of similar terrain to inside the protected area (Section 3): Over the last ~50 years, outside the protected area, there was a shift from livestock-based, subsistence agriculture and small-scale farming to a diversified set of ecosystem service uses. The combined area of grazing and wildflower harvesting declined by 39%, while the number of landowners using the mountains for personal nature-based recreation and ecotourism increased by 61% and 23% respectively. Agriculture intensified in suitable areas of mountain land with the number of landowners cultivating land increasing by 20%. Exogenous socioeconomic drivers associated with globalisation and economic growth were important causal mechanisms of land use change. Landowners valued mountain protection for intrinsic and non-use reasons (73-80% of landowners), including existence, bequest and option values, as well as for the indirect use of water supply (72% of landowners) in comparison with direct use reasons such as spiritual/cultural experiences and nature-based recreation inside the protected area (18 and 50% of landowners respectively). Personal, nature-based recreation outside the wilderness-protected area was associated with valuing the protection of mountain land for intrinsic and non-use reasons. Long-term vegetation change inside the protected area and plausible mechanisms driving vegetation change (Section 4): Inside the mountain protected area, fynbos vegetation cover increased on average between 11 and 30% and there were significant declines in bare ground and rock cover. In 5 accumulation and fire intensities. However, these latter changes in land use/cover also occurred outside the protected area (see results summarised for Section 3 above and Section 4 below) and therefore cannot be attributed to protected area establishment. Land use/cover and the influence on water flows inside the protected area compared to counterfactual scenarios of no protection (Section 5): Declines in grazing and changes to the fire regimes occurred regardless of the protected area boundaries. In the past, there was a high frequency of small, low intensity fires across the landscape, both inside and outside the protected area. More recently, fires have been actively suppressed and this resultsin the build-up of biomass and the development of extensive, high intensity fires which, under suitable conditions, burn large expanses of the mountain catchment. Hydrological modelling showed that a high intensity burning regime negatively affected streamflow regardless of protected area boundaries. Streamflow increased by more than 80% under high flow conditions and decreased by more than 40% under low flow conditions relative to an unburnt ‘natural’ scenario. Over the last 50 years there has also been a substantial increase in dams, buildings and roads and minor increases in cultivation outside the protected area. This has been avoided inside the protected area where these land use/cover classes declined. If the increase in these land use/cover types observed outside the protected area occurred inside the protected area this would have resulted in reductions in daily streamflow leaving the protected portion of the catchment. For example, outside the protected area reductions of 8% to 25% of streamflow were observed during mid and low flow conditions respectively, particularly during dry years, in comparison to a ‘natural’ scenario. In contrast, inside the protected area streamflow recovered from past conditions to more closely resemble the natural flow conditions of the catchment. Therefore, had the protected area not been established there would have been losses in streamflow from the catchment as well as an increase in the degree of fragmentation within this mountain area. However, with increased water storage and fragmentation outside the protected area has also come increased socio-economic opportunities such as employment and local opportunities for ecotourism and sustainable agriculture e.g. indigenous cut flows. This highlights the importance of maintaining various forms of land management systems (multifunctional landscapes) within mountain ecosystems but also the need to understand the sustainability of different land management system types. Determining appropriate land management systems for mountain areas should be based on a full understanding of the impacts on ecosystem service benefits and costs at local and regional levels between social groups both spatially and temporally. Broader significance: This thesis contributes to the conservation literature on two main fronts. Firstly, it contributes conceptually and theoretically to understanding the dynamics of ecosystem services in relation to mountain protection. Secondly, it contributes methodologically by using an inclusive, trans- and interdisciplinary research approach for evidence-based conservation at a place-based and landscape level. The study provides a case 6 study example of the positive impact that mountain protection has on water-related ecosystem services, notably by maintaining streamflow throughout high to low flow periods and during dry years. It also provides clear evidence that ecosystem service trade-offs do not remain constant over time and shows that intrinsic and non-use values are required when describing the importance of mountain protected areas. In terms of understanding the impact that protected areas have in mountain regions, the research shows that complex processes are at play that extend beyond the boundaries of a specific protected area in both time and space. Interactions between global and local drivers were found to be prominent causal mechanisms of socio-ecological change and ultimately determined the influence of mountain-protection on land use/cover, fire, vegetation and water-related ecosystem services. The thesis emphasises that counterfactual framings are necessary to understand and attribute the impacts of protected areas on environmental outcomes, however pluralism and socio-ecological approaches are critical to determine plausible counterfactual conditions. This thesis focused only on landowners adjacent and proximal to the protected area owning the majority of mountain catchment land of similar terrain. It is likely that multiple socioeconomic trade-offs have occurred between different social groups and generations at both local and regional levels. Understanding how the disadvantages and benefits of the impacts of protected areas are apportioned across the landscape and temporally is an aspect that requires future research. Central to this would be to fully consider how human well-being is influenced both upstream and downstream, including at regional levels, and between social groups and across generations. Considering the impact of protected areas on the full range of ecosystem services and linking this to societal preferences and perceptions should be incorporated into the overall goal of developing an evidence base for conservation. This is because it is both scientific evidence and societal change that can determine protected area persistence and thus long-term protected area impact.
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    Open Access
    A remote sensing assessment of irrigation land use land cover change in the Sokoto Rima River Basin, Nigeria
    (2021) Abdulmajid, Aminu; Eckardt, Frank; Odera, Patroba
    This study examines the expansion and utilisation of Fadama irrigation in the Sokoto Rima River Basin using the ground yield and remote sensing data. Decadal land use land cover (LU/LC) change detection was conducted using remotely sensed data from Landsat 4,5,7 ETM for 1988, 1998 and Landsat 8 OLI for 2018 using a digital classification and a cloud-based classification provided by Google Earth Engine (GEE) API, with an overall accuracy of 97% in 1988, 92% in 1998 and 90% in 2018. Additionally, the Normalised Difference Vegetation Index (NDVI) derived from MODIS, GEE NDVI, and the Landsat was used to assess the crop yield patterns of the irrigation farming at the Fadama sites in conjunction with the limited ground yield data from 2000-2005, and was found to be a positive change over the years. The result generated from the classification was juxtaposed with observable field characteristics of the LU/LC identified. The decadal trend between 1988 to 1998 saw an increase of 114% in dam surface water and 166% of the natural vegetation, while the nonvegetated areas and the Fadama areas decreased in size by -100% and -65% respectively. Between 1998 and 2018, the reverse of the previous pattern was observed, with water and vegetated areas decreasing in their surface area in hectares by -80% and -23% respectively. Non-vegetated areas increased by 3% while Fadama areas increased in size by 112%, indicating that the Fadama areas were under-utilised by - 65% of the total hectarage in the past, and in recent years a 47% increase was recorded between the two periods. In addition, the Standardised Precipitation and Evapotranspiration Index (SPEI) data from 1950 was used to analyze the meteorological and hydrological drought pattern at four locations within the basin and was found to be a moderate drought. The SPEI data was then correlated with the Global Surface Water Explorer data to observe the surface water dynamics and to show the drought extent around Bakolori, Goronyo, Jibia, Wurno and Zobe dams. The result showed that the dams are shrinking in size due to risen temperature and consequent evaporation caused by moderate drought and water use for irrigation. Lastly, this research uncovers the utilization of the Fadama in recent years by 47%, but with mismanagement of the resources in the Sokoto Rima River floodplain because not all the irrigation fields are put into cultivation, with 39,907 ha put into use from the planned irrigation of 105,472 ha in the entire basin. Therefore, this research recommends a proper intervention of the government to promote and enhance sustainable management of the Fadama lands, water, and the vegetation resource. This should be done in consideration of the deteriorating climate to close yield gaps, with much emphasis on engaging the local farmers by monitoring yearly ground yield data and ensuring all incentives are distributed effectively to brace an active and sustainable management of the entire basin and its vast resource.
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    Aeolian dust emission dynamics across spatial scales: landforms, controls and characteristics
    (2018) von Holdt, Johanna R C; Eckardt, Frank; Wiggs, Giles; Hipondoka, Martin
    Variable erodibility (surface characteristics) and erosivity factors (meteorological conditions) result in dust emission dynamics being complex in both space and time. Accounting for localscale surface variability is critical to our understanding of dust emitting processes. This study identifies mineral dust using remote sensing, establishes emission thresholds through field measurements and identifies particle chemistry for major dust sources in the Central Namib Desert. Examining over 2000 Landsat images over a period from 1972 to 2016, identified 40 days of visually detectable dust, originating from sub-km scale point sources. The observations suggest that dust sources can be identified at the landform scales which particularly include ephemeral river valleys and saline pan surfaces. These persist throughout the 25-year record; however, a gradual shift in source point clusters is noted through time, which can be tentatively attributed to anthropogenic modification of the hydrological systems. A PI-SWERL (Portable In-Situ Wind ERosion Lab) wind tunnel was used to measure the emission potential of the Landsat derived targets. The most emissive sources were paleostockpiles of alluvial silt deposits and associated degraded nebkhas within the Kuiseb River Delta. These had a geometric mean emission flux of 0.076 mg m-2 s -1. In comparison, the active channel had a geometric mean emission flux of 0.008 mg m-2 s -1, undisturbed desert pavement 0.007 mg m-2 s -1, pan surfaces 0.001 mg m-2 s -1 and wadis within the gravel plains 0.030 mg m-2 s -1. The emission thresholds were augmented with site-specific field measurements such gravel cover (%), moisture content (%), particle size (µm), elemental composition (%) and shear and compressive strength (kg cm-2). A Boosted Regression Tree (BRT) machine-learning algorithm identified the most important surface and sediment characteristics determining dust emission from the measured surfaces. The model explained 70.8% of the deviance in the measured dust flux with the top predictor variables and their relative importance (%) as follows: gravel cover, 16%; moisture content, 14%; kurtosis, 13%; very coarse silt, 13%; very fine sand, 11%; fine sand, 8%; compressive strength, 7%, calcium, 7% and magnesium, 6%. Such an analysis can be used to identify critical thresholds for dust emission and standardise testing protocols. Linking landforms with such emission measurements allow for the assessment of two existing dust emission schemes: the Preferential Dust Scheme (PDS; Bullard et al. 2011) and the Sediment Supply Map (SSM; Parajuli et al. 2017). Although these schemes represent a major advance in our representation of dust emission source areas and erodibility, this study shows that these schemes still need to be improved to accurately depict dust emission potential. For the PDS this would include producing a global rasterised output with quantified dust emission potential and for the SSM, a more accurate classification of the highly emissive geomorphic units. Landsat source point sediments were subjected to physical and geochemical analyses and compared to samples obtained from passive collectors such as the Big Spring Number Eight (BSNE) and active PI-SWERL exhaust emissions, using an auto-SEM (QEMSCAN). This provided individual particle mineralogy (>2 µm resolution) for a total of approximately 10000 to 60000 particles per sample which enabled a comparison of particle size, shape and mineralogy. The samples consist of a mixture of minerals reflecting the varied metamorphic geology and consists predominantly of feldspar, quartz, mica, other aluminosilicates such as the alteration products epidote and chlorite and low to medium grade metamorphics such as amphibole and pyroxene, iron oxihydroxides, titanium minerals, carbonates and clay minerals.
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    The application of the surface energy balance system model to estimate evapotranspiration in South Africa
    (2013) Gibson, Lesley Anne; Eckardt, Frank; Jarmain, Caren; Su, Bob (Z)
    In a water scarce country like South Africa with a number of large consumers of water, it is important to estimate evapotranspiration (ET) with a high degree of accuracy. This is especially important in the semi-arid regions where there is an increasing demand for water and a scarce supply thereof. ET varies regionally and seasonally, so knowledge about ET is fundamental to save and secure water for different uses, and to guarantee that water is distributed to water consumers in a sustainable manner. Models to estimate ET have been developed using a combination of meteorological and remote sensing data inputs. In this study, the pre-packaged Surface Energy Balance System (SEBS) model was used for the first time in the South African environment alongside MODerate Resolution Imaging Spectroradiometer (MODIS) satellite data and validated with eddy covariance data measured in a large apple orchard (11 ha), in the Piketberg area of the Western Cape. Due to the relative infancy of research in this field in South Africa, SEBS is an attractive model choice as it is available as open-source freeware. The model was found to underestimate the sensible heat flux through setting it at the wet limit. Daily ET measured by the eddy covariance system represented 55 to 96% of the SEBS estimate, an overestimation of daily ET. The consistent underestimation of the sensible heat flux was ascribed to sensitivities to the land surface air temperature gradient, the choice of fractional vegetation cover formula as well as the height of the vegetation canopy (3.2 m) relative to weather station reference height (2 m). The methodology was adapted based on the above findings and was applied to a second study area (quaternary catchment P10A, near Grahamstown, Eastern Cape) where two different approaches for deriving surface roughness are applied. It was again demonstrated that the sensible heat flux is sensitive to surface roughness in combination with land surface air temperature gradient and again, the overestimation of daily ET persisted (actual ET being greater than reference ET). It was concluded that in complex environments, at coarse resolution, it is not possible to adequately describe the remote sensing derived input parameters at the correct level of accuracy and at the spatial resolution required for the accurate estimation of the sensible heat flux.
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    Characterising South Africa’s major dust sources
    (2019) Bekiswa, Sisanda Ongeziwe; Eckardt, Frank
    The study investigates the surface controls of major dust emissions and determines the patial distribution of major dust source in South Africa. This study follows a multi-disciplinary approach where primary and secondary data were used. The main objective of the study is to determine the spatial distribution of South Africa's Major Dust Sources. Meteosat Second Generation (MSG) satellite imagery, land use and land cover maps were used to achieve the first and the second objectives of the study. Primary data involved sampling 30 soil samples in the field in order to achieve the third objective of the study. The crust, soil moisture, soil texture and grain size are all controls of dust emission. This investigation is however focused predominantly on grain size characteristics. GIS methods were also used to determine soil type from the African soil map. Soil samples in both provinces were then collected to assess the Particle Size Distribution (PSD) of the soils. The particle size was determined based on a sieve analysis for grain sizes that were greater than 2mm and laser diffractometry, MasterSizer (Malvern) was used to achieve this. The results from the Malvern were later put to R Statistics where they were clustered into eight clusters to determine similarities and difference of the grain size. Because there is no uniqueness in the soil types found in the study area, there were no solid conclusions made based in them. The results show that the soil types are found across South Africa but not the same amount of dust activity was detected in the other parts of the country. Previous studies show that global significant dust sources are natural sources such as lakes, pans and depressions. However, results demonstrate that South African dust sources are anthropogenic sources resulting from commercial agriculture in semi-arid regions. This study has demonstrated that surface sediments suitable for dust production are a mixture of fine material, silt (50µm) and coarse material, sand (2000µm) and it appears that all clusters in this study all contained both mixtures and all have potential to emit dust.
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    Open Access
    The contribution of fog to the moisture and nutritional supply of Arthraerua leubnitziae in the central Namib Desert, Namibia
    (2018) Gottlieb, Tunehafo Ruusa; Eckardt, Frank; Cramer, Michael D
    Fog is a key source of moisture to the diverse coastal Namib Desert biota, delivering five times more moisture than rain. Apart from the importance of fog as a source of water for plants, it is also associated with particulates that may contain essential nutrients for plants. Furthermore, dry deposition can be an important input of nutrients to many ecosystems, but without water, dust deposited on leaves or on soil is inaccessible for plant uptake. In other studies of coastal ecosystems (e.g. Strandveld), it has been found that this combined deposition of nutrients represents a major source of nutrients to terrestrial ecosystems. In the case of the Namib Desert, the range of Arthraerua leubnitziae is limited to those areas where fog occurs. This study was carried out at five meteorological stations in the gravel plains of the Namib Desert, along an east-west transect increasing in elevation inland. I hypothesised that marine-derived deposition contributes to moisture and nutrient supply of Arthraerua leubnitziae, an endemic shrub restricted to the fog zone of the central Namib Desert, and consequently determines its distribution. To test this hypothesis, two sub-hypotheses were developed and tested independently. The first sub-hypothesis was that fog contributed to the distribution range of A. leubnitziae in the central Namib Desert and the second was that fog deposition has a significant potential to supply moisture and nutrients to A. leubnitziae in the central Namib Desert. To test the first sub-hypothesis, I measured fog and rain volume, and plant morphological characteristics at the five sites. In addition, a fog map was derived using climatic variables from the five sites and used with climate and edaphic variables in MaxEnt model of the probability of occurrence of A. leubnitziae. The occurrence of A. leubnitziae was found to coincide with areas with high fog occurrence with fog contributing 36% to the modelled distribution of A. leubnitziae alongside precipitation, elevation and isothermality. In order to test the second sub-hypothesis, I measured nutrients deposited in fog water derived from wet and dry deposition (Ca, K, Mg, Na, Cl, Br, NO₃, PO₄ and SO₄) and plant essential nutrients in plant and soil samples (N, P, K, Ca, Mg, Mn, Fe, Cu and Zn). I also determined the nutrient uptake by stems of A. leubnitziae. During the period of Sep 2015 to Aug 2016, fog provided 92% of the yearly water input across the study sites. Over the course of the sampling cycle, the total annual nutrient content of fog and dust was dominated by Ca and Na. Most of the nutrients (K, Mg, Na, and S) were of marine origin. However, Ca enrichment factors (relative to seawater) were higher than 1, suggesting an input from dust. A. leubnitziae was found to be able to directly intercept and absorb some of the nutrients in the dust and fog via their stems. Even though plant and soil nutrients did not match each other, a contribution to plant nutrition from dust and fog was evident. The low nutrient concentrations in the soils of the Namib Desert and significant inputs from dust and fog suggests deposition is an important source of nutrients for A. leubnitziae. Although work is still required to better understand the importance of fog water uptake for nutrient provision, I have identified that water, nutrients and environmental stress alleviation should not be considered separately in studying the role of fog as a determinant of plant distributions.
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    Elephant space use in relation to ephemeral surface water availability in the eastern Okavango Panhandle, Botswana
    (2023) Makati, Anastacia; Eckardt, Frank; Songhurs, Anna Catherine; Bennitt, Emily; McCulloch, Graham; Stronza, Amanda
    The movement and distribution of elephants can be influenced by environmental factors over time (Foley, 2002). Examining how features in the landscape such as vegetation productivity, water sources and anthropogenic activities drive the movement of elephants can help in understanding patterns of movement. It can also help to inform the establishment and alignment of protected areas, wildlife corridors and identification of tourism hotspots as well as policy interventions to manage Human-Elephant Conflict (HEC). The Okavango Panhandle in Botswana is a HEC hotspot and the focus of My study. A number of strategies to address HEC are underway in the area, however one longer term strategy that has been proposed in this area involves provision of artificial water sources to influence elephant movements and keep animals away from fields during the cropping season. However, an improved understanding of how elephants utilize their habitats in relation to natural ephemeral surface water and other factors that influence their movements from dryland habitats to the Okavango Delta resources is needed to inform such management decisions. My study seeks to establish the role of ephemeral surface water on elephant distribution in the eastern Okavango Panhandle, Botswana as well as assess the movement distribution of elephants in relation to the seasonality, proximity and spatial extent of water presence represented by ephemeral surface water. Time series analysis of water extent on ephemeral surface water of the eastern Okavango panhandle will be developed and overlaid with elephant movement datasets. Elephant collar data from 15 elephants (5 males and 10 females) in the eastern Okavango Panhandle, Botswana have been analysed and Home Range (HR) sizes estimated using Kernel Density Estimation (KDE). The relative importance/probability of environmental variables in determining elephants' movement based on the Utilization Distribution (UD) were computed using Generalized Linear Mixed Models (GLMMs). I utilized a remote sensing spectral index, namely the Automated Water Extraction Index (AWEI) to delineate ephemeral surface water in dryland (excluding permanent waters) of the study area. The results reveal that during the wet season, elephants were evenly spread out all over the study area until the early dry season (April-June) when the ephemeral waterholes dried up. Elephants moved southwards towards the permanent waters of the Okavango River, where there are many human settlements and farms. Male HR sizes were found to be bigger than those of female elephants. Wet season (early and late) home range sizes were also bigger when compared to dry season (early and late) HR size. Mean daily distances were computed to investigate the effect of season on elephant daily distances and the distances ranged between 5km and 6.8km in the late wet and in the early wet and late dry season respectively. The Resource Selection Function (RSF) analysis shows that water adjacent sites are preferred over distant ones and both sexes prefer areas with high NDVI, with this preference being more pronounced in males. The seasonal variation of water use is notable in that it affirms the importance of proximity to water for elephants and has implications for their management and HEC. For example, I found that ephemeral surface water has a significant role in influencing elephant spatial use in the area, particularly during the early and late wet season. As ephemeral pans dried and NDVI (vegetation greenness) decreased, elephants started to move closer to the Okavango Delta and consequently human settlements and fields. However, further investigations into the timing of movements away from ephemeral waterholes and the influence of other environmental factors on elephant movements in the area would be needed before any recommendations can be made regarding artificial water provision in this area.
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    Environmental change and soil organic carbon storage in a dust emission hotspot, Free State, South Africa
    (2023) Ndara, Nolusindiso; Eckardt, Frank; Palmer, A
    Drylands farming areas are subject to land cover or land use change, climate change, and a variety of land management practices which may contribute to dust emissions and soil loss, a common symptom of land degradation. The goal of this study was to establish how the shift in land cover or land use change affects the occurrence of dust and determine the climate constraints and mitigations to crop production with focus on the dustiest parts of South Africa in the Free State Moreover, the study wished to establish land management strategies suitable for enhancing the storage of soil organic carbon and associated ecosystem services. To investigate how the shift in land cover or land use affects the occurrence of dust from 2006- 2016, the study firstly identified the spatial and temporal changes of land cover (LC) using the 2000 and 2013-2014 land cover maps derived from Agricultural Research Council. The results showed that grassland is still dominating in 2013-2014 but has decreased by 22 % from 2000. Cultivated land on the other hand has increased by 26 % from 2000 to 2013-2014. Some of the changes seen in recent data might also be the result of the associated data products. The change is however continuous and significant as major LC changes occurred over long-time scales. Cultivated land and grassland are dominant land cover and cultivated land is substantially being used to meet the economic demand (international maize price). Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index (MODIS EVI) was used to assess vegetation cover for the site of the start of dust. MODIS EVI indicated that vegetation plays a significant role during the occurrence of atmospheric dust. Sparse vegetation (EVI ranging from 0 – 0.18) is directly proportional to dust production. Dust events were generally observed in cultivated land especially in 2015 and 2016. Moreover, findings showed that vegetation is not solely a factor that affects dust production; rainfall, temperature and wind speed also contribute. Crop and land cover data obtained from Department of Agriculture, Forestry and Fisheries (DAFF) identified the dominating crop and land cover around each dust source as fallow land, maize fields, and pasture. For instance, dust source August 29th 2006 had 11533 ha of fallow land and 10795 ha of maize, and dust source September 15th 2016 had 7737 ha of fallow land and 4599 ha of pasture which suggest that dust does not exclusively depend on the amount of vegetation but also on the type of vegetation. To achieve the second aim, the study used data from Climate Hazard Infrared Precipitation with Stations (CHIRPS), Agricultural Research Council (ARC) and Standardised Precipitation 2 Evapotranspiration Index (SPEI) to determine the variation of rainfall in Free State. SPEI data showed that drought is becoming prominent and severe in Free State (2005, 2012, 2014 and 2016). ARC data showed a slight increase (357-408 mm/year) from two stations and a slight decrease from the other two stations in rainfall from 2005- 2016 and CHIRPS data showed a slight decrease (458-404 mm/year) from all the stations during the same period. Both CHIRPS and ARC data showed that there is a seasonal shift on the onset of rainfall; rainfall has shifted to late summer by approximately 62 days on average from 1981-2019 in Free State. Rainfall in Free State is becoming late (e.g., in 2011 rainfall adequate to make the soil moist was received in November) and number of rain events are decreasing (e.g., September 1981-2019 had 7 rainfall events greater or equal to 15 mm/day, 19 events in October, 52 events in November and 33 in December in Bultfontein weather station). This study used temperature data from ARC weather stations to determine how temperature and frost variation affect crop production in Free State. Findings indicated that temperatures have increased by ~ 1- 2 ○C in Free State and frost has decreased, and its onset has shifted by ~ 11 days. Frost occurred in Julian day of the year (DOY) 144 in 2005 and in 2016 there was no frost for the whole year in Bultfontein. The onset of frost is shifting to May and resulting to frost period decreased over the years. Decrease in frost is an advantage for crops that are planted in late summer, however increased temperatures are likely to result in crop failure, especially if rainfall is also low. Furthermore, the relationship between wind speed and dust occurrence was determined using the ARC and ERA5 datasets. The results showed that some years were characterised by high winds and some by low winds but generally there is no constant trend. The ARC maximum wind speed was 10 - 15 m/s and ERA5 maximum wind speed was 10 m/s. Both datasets showed that high wind speed occurs from August- November and many dust events are observed in these months. Additionally, high winds are mostly observed to occur on surfaces with sparse vegetation and in the absence of wind breaks which further promotes an increase in dust. Thus, it is important for farmers to leave crop residues after harvesting and practice moderate grazing. To achieve the third aim, the study further established land management strategies suitable for enhancing the storage of soil organic carbon. Soils sampled in 2019 from different sites in Free State were used to determine the amount of carbon and nitrogen. It is apparent that grassland can store more carbon especially in the Lixisols which appeared to have stored an average carbon of 1.23 g and maximum of 1.86 g from 0-2 cm to 20-30 cm depths. Moreover, cultivated land can store less carbon especially in the Arenosols which stored an average of 0.18 g and 3 maximum of 0.22 g from 0-2 cm to 30-45 cm depths. Findings suggest that grassland can store more carbon than cultivated land due to minimal disturbance of the land when compared to cultivated sites. Moreover, the study demonstrated that soil texture and grain size distribution play an additional role in carbon storage with higher loads linked to higher silt content (Lixisols) and less carbon being stored in soils with high sand content (Arenosols). More carbon was observed to be stored in soils with moderate sand content (Lixisols = 40 % of sand) and high silt content (54 %) and less carbon was stored in soils with high sand content (Arenosols = 80 % of sand) and moderate silt content (18 %). More carbon was shown to be stored in the top layers of the soil 5-10 cm and was observed to decrease with increasing depth. DAYCENT carbon model was further used to simulate soil carbon in different land management scenarios to come up with suitable land management options for storing more carbon in future. Results illustrated that native grassland can substantially store more carbon than cultivated land, however moderate grazing should be applied. This would allow for a reduction of future dust emissions and increase ecosystem services in the cultivated lands of the Free State. Overall, the study demonstrated that combining the investigation of LCLU, climate change and land management was important to better understand land degradation and identified possible mitigation measures.
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    The evolution of the Congo- Kalahari Watershed: African mega-geomorphology
    (2014) Flugel, Tyrel James; Eckardt, Frank; Cotterill, Fenton
    Africa's bimodal elevation, low in the north and west, and high in the south and east, is globally unique. The Congo–Kalahari Watershed represents the transition between low and high Africa. This sub–continental drainage divide separates two of the world's large rivers: the Congo and Zambezi Rivers. This study focuses on the large rivers which form the Congo–Kalahari Watershed. The analysis of their longitudinal profiles, through the use of a geographic information system and remotely sensed imagery and elevation data, provides insights into this drainage divide. The creation of a geodatabase on river knickpoints, featuring geographic and geologic attributes for 18 longitudinal river profiles represented by 194 047 elevation points (19 700 km), identifies a total of 380 knickpoints, 243 of which have heights larger than 5 m. It is possible to assign a probable cause to 354 of all the knickpoints identified in this study, highlighting the underlying geology as a significant control with tectonics playing a secondary role. The following rivers are studied: Chambeshi, Congo, Kalungwishi, Kasai, Kwango, Luapula, Lufira, Lukuga, Lulua, Luvua and Wamba (Congo Basin) and the Cubango, Cuchi, Kabompo, Kafue, Luena and Upper Zambezi Rivers (Kalahari Basin). It is argued that the Congo–Kalahari Watershed is a trimodal feature comprising of a western, central and eastern zone. The smooth central region of the divide is the oldest and has been relatively stable since the break–up of Gondwana. The western region is topographically rougher and has undergone substantial change in the Cenozoic becoming bifurcated by the headwater erosion of the coastal rivers. The eastern watershed is the youngest and topographically roughest, having been substantially modified in the Neogene due to tectonic activity associated with the extension of Western Branch. Due to the extensive modification, this eastern zone should be considered a new feature. The acknowledgment of these three landscapes may lead to the conciliation of various interpretations and suggested causes of Africa's present day continental geomorphology.
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    ‘Follow the Water’: Microbial Water Acquisition in Desert Soils
    (2023-06-27) Cowan, Don A; Cary, S. Craig; DiRuggiero, Jocelyne; Eckardt, Frank; Ferrari, Belinda; Hopkins, David W.; Lebre, Pedro H.; Maggs-Kölling, Gillian; Pointing, Stephen B.; Ramond, Jean-Baptiste; Tribbia, Dana; Warren-Rhodes, Kimberley
    Water availability is the dominant driver of microbial community structure and function in desert soils. However, these habitats typically only receive very infrequent large-scale water inputs (e.g., from precipitation and/or run-off). In light of recent studies, the paradigm that desert soil microorganisms are largely dormant under xeric conditions is questionable. Gene expression profiling of microbial communities in desert soils suggests that many microbial taxa retain some metabolic functionality, even under severely xeric conditions. It, therefore, follows that other, less obvious sources of water may sustain the microbial cellular and community functionality in desert soil niches. Such sources include a range of precipitation and condensation processes, including rainfall, snow, dew, fog, and nocturnal distillation, all of which may vary quantitatively depending on the location and geomorphological characteristics of the desert ecosystem. Other more obscure sources of bioavailable water may include groundwater-derived water vapour, hydrated minerals, and metabolic hydro-genesis. Here, we explore the possible sources of bioavailable water in the context of microbial survival and function in xeric desert soils. With global climate change projected to have profound effects on both hot and cold deserts, we also explore the potential impacts of climate-induced changes in water availability on soil microbiomes in these extreme environments.
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    Hydrochemical dynamics on sub-Antarctic Marion Island
    (2017) Stowe, Michael-James; Eckardt, Frank; Nel, Werner
    Although sub-Antarctic maritime environments are some of the most sensitive regions to climate change, investigations into isotopic and hydrochemical dynamics on sub-Antarctic islands are limited. To address this, the Soft Plume River on sub-Antarctic Marion Island was sampled daily along an altitudinal gradient during an intense high-resolution 16-day field campaign in April/May 2015. Samples were analysed for stable isotopes (δ²H and δ¹⁸O) and major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻ , SO4²⁻, NO³⁻). In addition, stream water physicochemistry (pH, water temperature, dissolved oxygen and total dissolved solids) was monitored in situ at a single site in the stream at 5 minute resolution for the duration of the field campaign. Monthly precipitation δ²H and δ¹⁸O had mean values of -27.51‰ and -4.67‰ respectively. Stream water δ²H and δ¹⁸O values were significantly different to that of precipitation, with values ranging from -48.0‰ to -33.6‰ and from -7.6‰ to -5.6‰, respectively. Major ion concentrations were dominated by Na⁺ and Cl⁻, reflecting the overwhelming influence of the surrounding ocean on the island's stream water chemistry. This finding is consistent with previous studies on Marion Island and other maritime sub-Antarctic islands. Temporal variability in stream chemistry was assessed through daily sampling. Findings show that variation was predominantly controlled by precipitation. Following high precipitation amounts low stream water δ²H and δ¹⁸O values were recorded. This was likely the result of the "amount effect". Similarly, a decrease in ion concentrations was also observed following high rainfall amounts. This was because of stream dilution. Sampling along the stream revealed that variation in δ²H and δ¹⁸O and most major ions was largest at the highest site. This pattern is likely the result of an altitudinal precipitation gradient, with higher amounts of precipitation falling at the highest altitude site. High-frequency monitoring of stream water physicochemistry revealed the presence of diel oscillations. Stream pH, temperature and dissolved oxygen concentrations all exhibited diel cycles. Stream pH and temperature were characterised by afternoon maxima and night time minima, with dissolved oxygen following an inverse cycle. These results are the first time diel cycles have been observed for stream water on Marion Island. Taken together, results from this study revealed that the Soft Plume River exhibited a noticeable degree of variability and complexity, especially as results only represent stream water chemical dynamics over a limited range of annual hydroclimatic variation.
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    Identification and monitoring of oil pipeline spill fire using space applications
    (2018) Gbenga, Ogungbuyi Michael; Martinez, Peter; Eckardt, Frank
    Oil pipeline spills in the Niger Delta cause a great deal of environmental damage to sensitive ecosystems and losses of many millions of dollars to the Nigerian economy every year. These spills occur along the routes of pipeline infrastructure and other oil facilities like flowlines, trunk lines, flow stations, barges, well heads etc. The causes of these spill events include: operational or maintenance error, ageing oil facilities, as well as acts of deliberate sabotage of the pipeline equipment which often result in explosions and fire outbreaks. In this project, we have investigated whether satellite observations could be used to detect these oil pipeline fires. The Nigerian National Oil Spill Detection and Response Agency (NOSDRA) database contains a total of 10 072 oil spill reports from 2007 to 2015. The space-based approach we considered in this dissertation included the use of data gathered by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites, which recorded 85 129 active fire hotspots in the Niger Delta from 2007 to 2015. Since the oil spill reports serve as validation data for these oil spill fires, we explored the capability of the MODIS instrument to study the spatio-temporal correlation between spills and fire events by attempting to investigate whether the largest spills by volume that resulted in fires could be detected from space in near-real time. Although the NOSDRA oil spill reports are plagued with several irregularities from the Joint Investigation Visits by the joint task force who visit spill sites, our approach in this dissertation automated the filtering process of the raw database to meet our research goal and objective. This study confirms that, indeed, fires resulting from oil spills are detectable using the MODIS fire products. For 43 of the largest spill events, we were able to establish a spatio-temporal correlation of spill incident reports with MODIS fires clearly associated with the oil pipeline infrastructure. Our study also shed light on the spatial and temporal characteristics of non-pipeline fires in the study area.
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    Lower Kuiseb River sediments and their control on dust emission
    (2013) Von Holdt, Johanna RC; Eckardt, Frank
    Previous studies, using remote sensing, have identified the Kuiseb River in Namibia as the dustiest river in Southern Africa. Dust plumes detected from this basin are mostly associated with the Lower Kuiseb River, between the end of the bedrock canyon at Natab and the Kuiseb Delta towards the Atlantic Ocean. The purpose of this study was to examine the surface materials of the Lower Kuiseb River and establish their potential towards dust production, leading to such plumes. This investigation focused predominantly on the size characteristics of 153 surface sediment samples collected from the Kuiseb main channel, its terraces, delta, gravel plain surfaces and tributaries, dunes and interdune, all of which were analysed using a Malvern Mastersizer 2000 laser diffractometer. In addition, other sediment characteristics such as mineralogy, organic matter content, soluble salts; and selected surface roughness elements were also considered. Furthermore MODIS satellite imagery was used to assess the dust emission activity from each of the geomorphological units sampled in the field for the period from 2005 to 2013. This study has demonstrated surface sediments suitable for dust production to increase towards the coast with particular "dusty" floodplain surfaces between Swartbank and Rooibank, as well as the Kuiseb Delta. It appears that silt crusts formed as the flood water dissipate, provide a main source of appropriately sized material for deflation. The crusts consist entirely of silt and clay sized material, with a maximum of 97% <63μm, 39% <10μm and 6% <μm. Dust producing surfaces of the gravel plain include the gravel plain drainage, which has the largest quantity of clay sized material (maximum of 11% <μm). Anthropogenic disturbances of the surface are likely playing a role in the production of dust, with livestock farming causing a fragmentation of crusts in the river valley, and mining and off-road driving disturbing the gravel plain.
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    The nature of pan sediments: A case study on dust supply from the Makgadikgadi pans, Botswana
    (2014) Vickery, Kathryn J; Eckardt, Frank
    Understanding dust sources is essential, as aerosols from arid basins have widespread effects on atmospheric, biological and terrestrial processes on regional to global scales. This thesis presents the results of chemical and morphological analysis for sediments from Sua Pan, Botswana, which forms part of the Makgadikgadi Basin, southern Africa's most productive dust source. The analysis was performed in order to evaluate pan sediment characteristics and erosivity controls including the analysis of weather and climatological conditions. We analysed 41 grab samples consisting of crusts, fluff, and soil from 12 locations within a 144 km² grid (centred on 25.959°E and -20.5754°S) as well as 6 airborne samples collected using frisbees, BSNE traps and PI-SWERL exhaust, between July and October 2011. Dry sieving and laser diffraction for all 41 samples revealed a dominance of uni-modal, sand sized sediments, with the particle size distribution controlled by evaporite minerals, inferred from sample digestion. XRD and ICP analysis on 8 and 22 samples respectively, identified evaporite minerals including halite, thenardite, mirabilite and trona, in addition to carbonate minerals, which represent the young transient mineralogy of the pan. Older metal oxides were also present, originating from parent substrates. The addition of QEMSCAN analyses performed on 5 airborne and 1 surface sample, identified feldspar and pyroxene, along with quartz in its amorphous state, which was further confirmed through SEM analysis. QEMSCAN evaluated 255 minerals, many of which were below the detection limits of the 20 minerals identified through XRD analysis. QEMSCAN further attributed mineralogy and morphological detail to 27 000 individual grains per sample, positively linking airborne samples with their surface source. Seven years of twice daily MODIS images were analysed to identify the emission signature of the Makgadikgadi complex, revealing a number of synoptic states associated with emissions, peaking in July and driven largely by ridging anticyclones. The emission signature of the pans revealed that they respond to diurnal, seasonal and inter-annual controls, moisture dynamics and crust conditions with anthropogenic stresses also being evident. This study has interpreted the driving mechanisms and limitations associated with both the micro and macro scale of dust entrainment, advancing the current understanding of the Makgadikgadi as a dust source through interpreting these controls at the local scale.
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    Urban growth in Southern Africa : comparing 30 years of decadal imagery to census data
    (2011) Lewis, Lauren Lyn; Eckardt, Frank; Battersby-Lennard, Jane
    The total urban area of each study site was calculated for each time slice and the results were represented as maps depicting urban expansion. Graphs were also created depicting the total urban area vs. total population for each time slice (1970s, 1990s and 2000s).
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    Using an airborne hyperspectral and LiDAR integrated sensor approach to spectrally discriminate and map savanna bush encroaching species in the Greater Kruger National Park region
    (2011) Naidoo, Laven; Mathieu, R; Cho, M; Eckardt, Frank
    Bush encroachment is an environmental phenomenon which affects arid and semi-arid savanna rangelands across the world. Bush encroachment has numerous negative and positive impacts on these savanna ecosystems depending on the land use practices and associated rangeland management regimes.