Arid and semi-arid regions have increasingly become the subject of much research and debate by scientists. By their very nature, these regions characteristically exhibit extremes which complicate the implementation of effective management strategies that ensure sustainable productivity and economic output. Namibia is one such region where low and highly variable rainfall conditions and fluctuating productivity pose a challenge to managers of commercial livestock enterprises, / who seek to optimise economic benefits while controlling the negative effect on herd production and income of unpredictable and unfavourable climatic events. Various management approaches are proposed as a means of exploiting periods of abundant productivity and so optimising income from herd production, while controlling for the effects of drought conditions. To analyse the effects of these various offtake strategies, a rainfall-driven plant-herbivore simulation model is used. The model comprises components simul~tihg vegetation and herbivore dynamics. The vegetation component incorporates soil moisture and nutrient allocation to plant parts. The herbivore dynamics sub-model comprises age and sex classes, population dynamics and animal energy requirements which govern accumulated fat reserves. The model is adapted to account for climatic and vegetation attributes specific to Namibia. An economic component including a seasonal monthly price structure is developed, and a dynamic feedback governing management decisions is incorporated. The much debated issue of whether to maintain a constant stocking rate or to track climatic variation by employing a variable stocking level is investigated, with the performance of management strategies incorporating these approaches ranked according to various factors, including annual returns, associated risk and annual stock mortality. The economic consequences of the timing of offtake are investigated, with the simulation of management strategies that implement destocking in the face of anticipated drought conditions. A dynamic projection of expected income allows the impact of forecasting potential economic gains on decision-making to be analysed. Results indicate that the performance of management strategies is not as dependent on climatic and seasonal price variability as was originally expected, with the application of a constant stocking level proving to be the most favourable strategy in terms of economic gain and variability of income. Tracking climatic variation by adapting stocking levels does not provide the improvement in economic returns from a livestock production system that was anticipated, although this approach is successful in effecting a significant reduction in annual stock mortality. Further results show the sensitivity of income to the long-term average stocking level characterising the management strategies investigated, as well as to the elasticity of the underlying price structure. The results of this study indicate that the implementation of management strategies designed to track climatic variation does not offer significant economic advantages over the application of a constant stocking approach. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Bibliography: leaves 146-152 / 152 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Plant Pathology, Waite Agricultural Research Institute, University of Adelaide, 1987

Thesis (Ph. D. - Arid Lands Resource Sciences)--University of Arizona, 1983. / Includes bibliographical references (leaves 164-170).

Thesis (Env. Mgt.(Hons.))--University of Adelaide, Dept. of Environmental Science and Management, 1998. / Bibliography: leaves 52-58.

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The effects of roads on landscapes and wildlife and their ecological processes are substantial and represent a major anthropogenic disruption to the natural environment. Current understanding of the impacts of roads for their strategic management is hampered by a lack of information on 1) the influence of the ecosystems on road effects, 2) the effects of roads on higher-order ecosystem responses (populations and communities), and 3) the overall impacts of roads on ecosystems and their wildlife (on both abiotic and biotic ecosystem components). This study used the Silver City Highway in arid New South Wales, Australia, as a model for a typical road in an arid ecosystem to investigate the ecological effects of arid-zone roads and their management. The study examined the spatial variation of soil, vegetation, kangaroo and small mammal variables in relation to the road, explored the factors contributing to these respective spatial variations, investigated the effects of arid-zone road management on vegetation, assessed the fragmentation effect of the arid-zone road on small mammals, and determined the patterns, causes and effects of kangaroo-vehicle collisions. The study revealed that the arid-zone road influenced most of the variables measured, skewed the population demographics of two kangaroo species, and altered the community composition of small mammals, with two small mammal species listed as threatened in NSW and of national significance (Sminthopsis macroura and Leggadina forresti) negatively impacted by the road. Increases in the amount of water along the road edge drove many of the subsequent effects of the arid-zone road as arid-zone flora and fauna are adapted to exploiting limited and patchily distributed resources. However, current arid-zone road management also influenced vegetation quality, microclimates around the road influenced kangaroo densities and small mammal communities, and kangaroo flight behaviour and temporal variations in traffic volume affected roadkill frequency. Together, these results suggest that roads have a high overall ecological impact in arid ecosystems. Conservation managers need to first rank the impacts of arid-zone roads in order of their conservation importance and need for mitigation, and from there, devise relevant informed management frameworks to target these impacts.

Dryland salinity is a major and expanding threat to agricultural land in Australia. Animal production from forages grown on saline land is perhaps its most promising economic use. Glycophytic forage legumes have been evaluated under saline conditions mainly for agronomic characteristics and, to a lesser extent, for nutritive quality to animals. Plant growth and its nutritive quality are interrelated, but a decline in yield in response to salinity may be associated with effects on the chemical constituents of the plant since soil salinity affects plant metabolism. This research aimed to investigate changes in the components of yield and nutritive value of two legumes species. Lucerne ( Medicago sativa ) and Melilotus ( Melilotus albus ) were exposed to different levels of NaCl in the range of 0 to 110 mM NaCl. The research tested the hypothesis that the components of plant nutritive value are not as sensitive to salinity as shoot biomass production since the adaptive mechanisms of the plant lessen harmful effects of the salts. For both plant species, salinity decreased leaf and stem dry matter production, but increased leaf - to - stem ratio. In addition, salinity resulted in earlier flowering in Melilotus. Mineral composition was the most sensitive component of forage quality. Calculated sodium chloride concentrations were up to 125 g / kg DM in lucerne and 39 g / kg DM in Melilotus when irrigated with 110 mM NaCl. The concentrations of calcium and magnesium decreased in both species and approached the marginal range for animal production. Zinc concentration also decreased while potassium decreased in stems of lucerne only. The digestible organic matter ( DOMD ) in response to salinity varied between species. At the highest salt concentration, the whole shoot ( i.e., leaf and stem ) of lucerne decreased up to 4 percentage units while Melilotus increased by 6 percentage units. In lucerne, DOMD was influenced by a high concentration of soluble ash in leaf and stem and, in Melilotus, by an increase in the organic matter content of leaf and a reduction in lignin concentration in stem, which favoured higher digestibility. These results were supported by a histological study in which an increase in starch in Melilotus leaf, and a lower proportion of xylem in relation to parenchyma in stems, was measured. Crude protein concentration was not compromised and, in relation to Melilotus, coumarin concentration did not increase with salinity. In conclusion, the reduction in DM production of species with similar salt tolerance does not necessarily correspond to an equivalent reduction in nutritive value. This research represents the most detailed study into effects of salinity on glycophytic forage legumes. Results show that while some aspects of forage quality ( e.g., minerals composition and energy ) are strongly influenced by salinity, other aspects ( e.g., protein ) remain relatively unaffected. These findings have implications for development of productive grazing systems on saline agricultural land. / Thesis (Ph.D.)--School of Agriculture, Food and Wine, 2006.

Dryland salinity is a major and expanding threat to agricultural land in Australia. Animal production from forages grown on saline land is perhaps its most promising economic use. Glycophytic forage legumes have been evaluated under saline conditions mainly for agronomic characteristics and, to a lesser extent, for nutritive quality to animals. Plant growth and its nutritive quality are interrelated, but a decline in yield in response to salinity may be associated with effects on the chemical constituents of the plant since soil salinity affects plant metabolism. This research aimed to investigate changes in the components of yield and nutritive value of two legumes species. Lucerne ( Medicago sativa ) and Melilotus ( Melilotus albus ) were exposed to different levels of NaCl in the range of 0 to 110 mM NaCl. The research tested the hypothesis that the components of plant nutritive value are not as sensitive to salinity as shoot biomass production since the adaptive mechanisms of the plant lessen harmful effects of the salts. For both plant species, salinity decreased leaf and stem dry matter production, but increased leaf - to - stem ratio. In addition, salinity resulted in earlier flowering in Melilotus. Mineral composition was the most sensitive component of forage quality. Calculated sodium chloride concentrations were up to 125 g / kg DM in lucerne and 39 g / kg DM in Melilotus when irrigated with 110 mM NaCl. The concentrations of calcium and magnesium decreased in both species and approached the marginal range for animal production. Zinc concentration also decreased while potassium decreased in stems of lucerne only. The digestible organic matter ( DOMD ) in response to salinity varied between species. At the highest salt concentration, the whole shoot ( i.e., leaf and stem ) of lucerne decreased up to 4 percentage units while Melilotus increased by 6 percentage units. In lucerne, DOMD was influenced by a high concentration of soluble ash in leaf and stem and, in Melilotus, by an increase in the organic matter content of leaf and a reduction in lignin concentration in stem, which favoured higher digestibility. These results were supported by a histological study in which an increase in starch in Melilotus leaf, and a lower proportion of xylem in relation to parenchyma in stems, was measured. Crude protein concentration was not compromised and, in relation to Melilotus, coumarin concentration did not increase with salinity. In conclusion, the reduction in DM production of species with similar salt tolerance does not necessarily correspond to an equivalent reduction in nutritive value. This research represents the most detailed study into effects of salinity on glycophytic forage legumes. Results show that while some aspects of forage quality ( e.g., minerals composition and energy ) are strongly influenced by salinity, other aspects ( e.g., protein ) remain relatively unaffected. These findings have implications for development of productive grazing systems on saline agricultural land. / Thesis (Ph.D.)--School of Agriculture, Food and Wine, 2006.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The Okiep copper district in the north-western corner of South Africa is a region that has been mined for over 150 years. Most mining operations have ceased, but years of mining has left the area scattered with abandoned mining sites. Acids (as used in ore processing) together with acid mine drainage generated from tailings exposure, collectively referred to as AMD hereafter, are a contamination risk to water resources and the biodiversity of this arid area. This study focused on an abandoned copper processing pond located close to the town of Nababeep. The leaching pond is unlined and has been excavated in the shallow colluvial soils. The natural soils of the area are shallow (60 cm) (WRB – Arenosol; SA – Oakleaf). Formations of corroded granite-gneiss boulders are an indication of the corrosiveness of the AMD collecting in the pond. The AMD was collected from the pond in the dry season at its most concentrated form and the AMD had exceptionally high concentrations of Al (26.9 g/l), Fe (42.9 g/l), Mg (20.5 g/l), Cu (3.8 g/l) and Mn (3.4 g/l). Melanterite (FeSO4·7H2O), a soluble ferrous compound, was found to play an important role in the immediate release of Fe and sulfates. The pristine soils have a sandy texture (2–5.2 %clay). The minerals detected in the clay phase include illite, kaolinite, montmorillonite and quarts. Pristine soils show some degree of contamination with low pH (4.38–4.77) and high Cu and sulfate contents. Soils located in the processing pond, which have been exposed to AMD for an extended period of time, showed poorly crystalline phases to be present (indicated by a broadening of the XRD peaks for clay minerals). Saturation indices (SI) were determined for saturated paste extracts of the pond soils and the obtained SI values support the notion of dissolution of silicate clays, as the obtained SI values ranged between –1.3 and –11.77 for illite and –4.76 to 0.58 for kaolinite. Jarosite, a new phase, formed in the contaminated soil and is a sink for K. Long term weathering experiments of pristine soils exposed to AMD indicated that clay minerals are significantly weathered and altered, which was identified by observing the broadening of the clay XRD peaks. Fourier transform infrared (FTIR) spectra were generated by scanning clay samples of the weathered soil. Amorphous phases were confirmed by structured water bands with wavenumber values of 3700 and 3300 cm−1 for acid treated soil. Micrographs showed a more amorphous and corroded morphology in the acid treated soil. Metal retention experiments were conducted by exposing the pristine soil to AMD repeatedly. Iron was the predominant metal attenuated in the soil. Metals such as Al, Mn, Na, K, Ca and Co were released by the soil into solution. Removal of Si is associated with the dissolution of clay minerals. The pristine soil shows limited capacity to neutralize acidity and low capacity to retain metals when leached with AMD. Metals were predominantly extracted in the water soluble phase of the long term weathering treatments. Aluminium was the most mobile fraction, being extracted predominantly from the water soluble fraction (2035 mg/kg). Exchangeable and acid soluble fractions did not retain significant quantities of metals. In the soil from the processing pond, the reducible fraction had a high concentration of reducible Fe (21175 mg/kg) and Si (3070 mg/kg). The reducible fraction also had the highest concentration of Cr (15.85 mg/kg), Cu (41.53 mg/kg), Pb (8.0 mg/kg) and Zn (10.65 mg/kg) compared to the other fractions of this soil. For the control experiment, the concentration of Cu (77.3 mg/kg), Pb (10.8 mg/kg) and Zn (24.1 mg/kg) were higher than contaminated soil yet lower for Cr (6.05 mg/kg). From these experiments, it can be concluded that the pristine soils studied have a limited ability to retain heavy metals in the non-bioavailable fraction, and, due to the nature of AMD, they are not effective in retaining metals sufficiently. The findings of this study suggest that the capacity of these pristine soils to buffer pH and retain metals is greatly limited. This could be as a result of (1) the low clay content, (2) the low concentration of secondary carbonates and (3) the low pH of the soil. The leaching of AMD from the pond is thus not regulated by the soils and poses a risk for nearby water resources. / AFRIKAANSE OPSOMMING: Die Okiep Koper Distrik, geleë in die noord-westelike hoek van Suid-Afrika, is ‘n streek waar mynbou al vir meer as 150 jaar plaasvind. Die meeste mynbou aktiwiteite is gestaak, maar jare van mynbou het die streek nagelaat met verskeie verlate mynbouterreine. Sure, wat in die prosessering van erts gebruik word, en suurmynwater wat gegenereer word uit die mynuitskot (gesamentlik verwys na as suurmynwater) is ‘n besoedelingsrisiko vir waterbronne en biodiversiteit in hierdie dorre area. Die studie fokus op ‘n verlate koper prosesserings aanleg naby die dorpie Nababeep. Die logingsdam is nie geseël nie en is uitgegrawe in vlak, kolluviale grond. Die natuurlike gronde van hierdie area is vlak (60 cm) (WRB – Arenosol; SA – Oakleaf). Formasies van weggevrete graniet-gneis rotse in die opgaardam is ‘n aanduiding van die bytende potensiaal van hierdie suurmynwater. Suurmynwater was versamel in die dam gedurendie die droë seisoen in die mees gekonsentreerde vorm. Die suurmynwater het besonderse hoë konsentrasies van Al (26.9 g/l), Fe (42.9 g/l), Mg (20.5 g/l), Cu (3.8 g/l) en Mn (3.4 g/l). Melanteriet (FeSO4·7H2O) is ‘n ysterhoudende verbinding en, alhoewel dit oplosbaar is, speel dit ‘n belangrike rol in die onmiddelike vrylating van Fe en sulfate. Die onversteurde grond het ‘n sand tekstuur (2–5.2 % klei). Die minerale wat in die klei fraksie ge-identifiseer is sluit illiet, kaoliniet, montmorilloniet en kwarts in. Die ongerepte gronde dui egter op ‘n mate van besoedeling deurdat dit ‘n lae pH (4.38–4.77) enhoë Cu en sulfaat inhoud het. Die grond wat geleë is naby die prosesseringsaanleg en ook blootgestel is aan suurmynwater vir ‘n verlengde tyd, dui daarop dat swak kristallyne fases teenwoordig is in die grond. Dit word bevestig deur ‘n verbreding van die XRD pieke van kleiminerale. Versadiging indekse (VI), wat bepaal is in versadigde grondekstraksies van die damgrond, ondersteun die oplossing van die silikaatkleie en word gereflekteer deur VI waardes wissel tussen –1.3 en –11.77 vir illiet en –4.76 tot 0.58 vir kaoliniet. Jarosiet is ‘n nuwe fase wat gevorm het in die besoedelde grond en is ‘n sink vir K. Langtermyn verweringseksperimente wat gedoen is deur die onversteurde grond bloot te stel aan suurmynwater wys beduidende verwering en verandering van klei-minerale deur verbreding van die XRD pieke. Fourier transform infrarooi (FTIR) spektra is op kleimonsters van die verweerde grond gegenereer. Amorfe fases is bevestig deur gestruktureerde waterbindings met frekwensies tussen 3700 en 3300 cm−1 vir suurbehandelde grond. Metaal-vasleggings eksperimente is uitgevoer deur herhaaldelik die onversteurde grond aan die suurmynwater bloot te stel. Yster is die metaal wat hoofsaaklik in die grond vasgehou is. Metale soos Al, Mn, Na, K, Ca en Co was vrygestel in oplossing deur die grond. Die vrylating van Si deur die grond word geassosiëer met die oplossing van kleiminerale. Die onversteurde grond toon beperkte vermoë om suur te neutraliseer en metale te bind in die grond wanneer dit met suurmynwater geloog word. Metale was hoofsaaklik ge-ekstraëer in die wateroplosbare fase vir die langtermyn verweringsbehandelings. Aluminium was die mees mobiele fraksie wat ontrek is van die water oplosbare fraksie (2035 mg/kg). Uituilbare en suuroplosbare fraksies het nie ‘n groot hoeveelheid metale vasgehou nie. Gronde wat versamel is naby die prosesseringsdam het die hoë konsentrasies vanFe (21175 mg/kg) en Si (3070 mg/kg) in die gereduseerde fraksie gehad. Die reduserende fraksie het ook die hoogste konsentrasie van Cr (15.85 mg/kg), Cu (41.53 mg/kg), Pb (8.0 mg/kg) en Zn (10.65 mg/kg) gehad in vergelyking met ander fraksies in die grond. Vir die beheer eksperiment was die konsentrasie van Cu (77.3 mg/kg), Pb (10.8 mg/kg) en Zn (24.1 mg/kg) hoër as in die besoedelde grond en laer vir Cr (6.05 mg/kg). Dus kan daar van hierdie eksperimente afgelei word dat die onversteurde grond beperkte kapasiteit het om swaar metale in grond vas te hou in die nie-biobeskikbare fraksie. As gevolg van die aard van die suurmynwater, is die grond nie voldoende om die metale effektief in grond te behou nie. Die bevindinge van hierdie studie dui daarop dat die kapasiteit van die ongerepte grond om pH te buffer en metale in grond te behou baie beperk is. Dit kan toegeskryf word aan die lae kleiinhoud, lae konsentrasie van sekondêre karbonate en die lae pH van die grond. Die loging van suurmynwater van die logingsdam is dus nie gereguleer deur die gronde nie en stel die naasliggende waterbronne in gevaar.