Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The passive recovery of old fields in the Karoo is a slow process, hampered by low and erratic rainfall, poor seed germination due to limited availability of suitable micro sites for seedling establishment, competition from existing vegetation, altered soil properties and the reduction of key soil biotic processes. The objectives of the study were to investigate the role of seed banks in the recovery of old fields, and to identify possible plant species and methods of establishing these species with the primary aim of initiating the process of succession / recovery of old fields in the Little Karoo. The investigation of the seed bank addressed the following issues: the resemblance of the seed bank to the above-ground vegetation in an old field and the effect of disturbance on the seed bank. Furthermore, the role of propaguie migration was investigated to establish possible propaguie movement from undisturbed to disturbed areas was investigated. The study indicated that the perennial seed bank had a 31 % similarity to the above ground vegetation in the old field. The seed bank was dominated by annual species. In the above-ground vegetation perennial canopy cover was higher compared to annual cover. The perennials with the highest densities in the soil seed bank were disturbance-adapted species with little importance for grazing animals except perhaps in the short-term. Disturbance caused annual densities to increase and perennial densities to decrease. The investigation of propaguie migration compared adult canopy cover and seedling densities. The results show that perennial distribution was patchy and that propaguie migration is low to non-existent. This led to the conclusion that old fields require supplemental seed additions. A total of seven species were assessed for their restoration potential. The species used in the investigation were Tripteris sinuata, Ruschia spinose, Drosanthemum speciosum, Indigofera sessifolia, Pteronia incana, Ehrharfa calycina and Chaetobromus dregeanus. Seed viability was examined using one of two techniques ie. tetrazolium or a standard germination technique. The optimal temperature for germination was determined using the following temperature regimes: 15°C day / 1DoC night, 20°C day /1 DoC night and 30°C day / 15°C night. The temperature range with the best performance was 20°C day / 1DoC night indicating that species should be sown in autumn or early winter. This timing coincides with the onset of rains in this region. The field trial investigated the influence that various mechanical cultivation techniques (ploughing, disking, tilling and clearing) and soil amendments (seed, seed+aquasorb and seed+straw+branches) have on the establishment of the selected species. Seed germination and seedling survival was monitored. The influence of treatments on water infiltration and soil moisture was investigated. Only four of the seven species germinated (Tripteris sinuata, Ehrharta calycina, Chaetobromus dregeanus and Pteronia incana). As far as species performance was concerned, T. sinuata performed best followed by E. calycina and C. dregeanus, while P. incana failed to persist. The cultivation treatments that yielded the best results were tilling, disking and ploughing. Emergence success in cleared and untreated plots was relatively low. As far as seedling emergence was concerned the most appropriate soil amendments were seed+aquasorb, seed and seed+straw+branches. Although soil moisture was higher on-heuweltjies than offheuweltjies there was no significant difference in seedling emergence and survival between these localities. Even though soil moisture was higher in seed+straw+branches treatment than in seed+aquasorb and seed treatments, seedling emergence in this treatment were lower than in the two latter treatments. This clearly indicates that soil moisture is not the only factor that influences the establishment of species. In the trial a mixture of late successional and pioneer species were sown, primarily with the aim of initiating the process of succession! recovery of old fields. Contrary to what was expected the late successional species germinated first. This has led to the conclusion that these late successional species have no innate dormancy, further proved by the inability of species to germinate after the second season. It could thus be that these late successional species have a short live span, and that they germinate when conditions are favourable. It must also be kept in mind that the seed sown were freshly harvested, and it could be that the pioneer species needed an after-ripening period before they germinated. / AFRIKAANSE OPSOMMING: Die passiewe herstel van oulande in die Karoo is 'n tydrowende proses, wat vertraag word deur wisselvallige reënval, swak ontkieming as gevolg van 'n tekort aan geskikte mikro-habitatte vir saailingvestiging, kompetisie van bestaande plantegroei, veranderende grondeienskappe en die afname in sleutel biotiese prosesse. Die doel van hierdie studie was, om die rol van saadbank in die herstel van oulande te bepaal, sowel as om moontlike plantspesies te identifiseer en metodes van vestiging van hierdie spesies te bepaal met die primêre doelom die proses van suksessie / herstel van oulande in die Klein Karoo te inisieër. Met die saadbankstudie is die volgende punte aangespreek: die ooreenkoms tussen die meerjarige spesies in die saadbank en bogrondse plantegroei op ou lande, en die effek van versteuring op die saadbank. Verder is gekyk na die rol van voortplantingsmeganisme verspreiding om moontlike beweging vanaf onversteurde na versteurde areas te ondersoek. Die studie het aangedui dat daar 'n 31% ooreenkoms is tussen meerjarige spesies in die saadbank en die bogrondse plantegroei op ou lande areas. In die bogrondse plantegroei van die ou land was die kroonbedekking van meerjarige spesies hoër as die van eenjarige spesies. Die dominante meerjarige spesies in die saadbank was spesies wat aangepas is by versteurings, met min weidingswaarde, behalwe moontlik oor die kort termyn. Versteuring het In verhoging in eenjarige en In afname in meerjarige saailingdigthede veroorsaak. Resultate dui daarop dat meerjarige verspreiding onreëlmatig is in die versteurde area en dat die teenwoordigheid van voortplantingsmeganismes, baie laag is. Dit lei tot die gevolgtrekking dat oulande addisionele saad benodig vir hervestiging. 'n Totaal van sewe spesies is ge-evalueer vir hulle moontlike restorasie potensiaal. Die spesies wat in die ondersoek gebruik was, is Tripteris sinuata, Ruschia spinose, Orosanthemum speciosum, Indigofera sessitolie. Pteronia incana, Ehrharta calycina en Chaetobromus dregeanus. Die kiemkragtigheid van die spesies is bepaal deur gebruik te maak van een van twee tegnieke nl. die tetrazolium of 'n standaard ontkiemings tegniek. Die optimale temperature vir ontkieming is bepaal deur gebruik te maak van die volgende temperatuurreekse: 15°e dag / 1Qoe nag, 200e dag /10oe nag and 300e dag / 15°e nag. Die temperatuur reeks waarop spesies die beste presteer het, was 2DOC dag /1DOC nag. Dit dui daarop dat spesies tydens herfs en vroeë winter gesaai moet word. Dit is dan ook die tydperk vir die aanvangs van die reënseisoen in hierdie streek. In die veldproef is gekyk na die invloed van verskeie meganiese bewerkings - tegnieke (ploeg, dis, ghrop en plant verwydering) en grondverbeterings behandelings (saad, saad+aquasorb en saad+strooi+takke), op die vestiging van geselekteerde spesies. Saadontkieming en saailingoorlewing is gemonitor. Die invloed van die behandelings op waterinfiltrasie en grondvog is ook ondersoek. Slegs vier van die sewe spesies het ontkiem naamlik: Tripteris sinuata, Ehrharfa calycina, Chaetobromus dregeanus en Pteronia incana. Spesies wat die beste presteer het, was T. sinuata die gevolg deur E. calycina en C. dregeanus, terwyl P. incana nie oorleef het nie. Die bewerkingsbehandelings wat die beste vestiging van plante gegee het, was die ghrop en disbewerkings gevolg deur ploegbewerking. Ontkiemings sukses in areas waar plante verwyder is en onbehandelde persele was relatief laag. Die grondverbeterings behandeling wat die beste ontkieming gelewer het was saad+aquasorb gevolg deur saad en saad+strooi+takke. Alhoewel grondvog hoër was op heuweltjies as weg van heuweltjies, was daar geen betekenisvolle verskil in ontkieming en oorlewing tussen hierdie lokaliteite nie. Alhoewel grondvog hoër was in saad+strooi+takke behandelings as in saad+aquasorb en saad behandelings was ontkieming laer in hierdie behandeling as in die saad+aquasorb en saad behandelings. Dit dui dus daarop dat grondvog nie die enigste faktor is wat die vestiging van spesies beinvloed nie. In die veldproef is 'n mengsel van pionier en klimaks spesies gesaai, met die primêre doelom die proses van suksessie/herstel van oulande te inisieër. In teenstelling met wat verwag is het die meer klimaks spesies eerste ontkiem. Dit het gelei tot die gevolgtrekking dat hierdie spesies geen dormansie het nie, en dit is verder bewys deur 'n onvermoë om te ontkiem in die tweede seisoen. Dit mag wees dat die meer klimaks spesies 'n kort lewensduur het, en dat hulle ontkiem wanneer toestande gunstig is. Dit moet ingedagte gehou word dat die saad vars geoes was, en dit kon dus wees dat die pionier spesies 'n na-rypwordings periode benodig voordat hulle ontkiem.

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science. Johannesburg, South Africa, 2015. / Unable to load abstract

The main aim of this study was to test rehabilitation interventions in a system altered by heavy grazing, and to develop methods of monitoring these interventions.

The main aim of this study was to test rehabilitation interventions in a system altered by heavy grazing, and to develop methods of monitoring these interventions.

Approaching the ecological rehabilitation of an open-cast phosphate mine in the West Coast of South Africa during the post-operational phase presented some challenges. The area was extensively modified during the mining operations. Soils from different layers were mixed with topsoil being covered by subsoil, overburden dumps and tailing dams being constructed resulting in extensive cross-zoned soils. Large areas of subsoil areas were exposed on the mine floor with localized and small scale salinity being evident. The modified topography as well as the complex new surface material posed a challenge in terms of identifying suitable local species that could be used to rehabilitate the post-mining environment. The mine area was heavily infested with woody alien invasive plants, such as Acacia cyclops, established in an attempt to reduce the dust and little natural vegetation cover was present. In the arid west coast environment, the four-month-long winter growing season is followed by hot and windy dry summers (Chapter 2) presenting a challenge reestablishing local vegetation in modified soils. Moreover, little was known about the local vegetation in terms of their propagation and use in stabilization techniques as an alternative to exotic vegetation such as the A. cyclops, which had been more often used in revegetation projects. A study was conducted to determine the most efficient and cost-effective methods of vegetative rehabilitation of the Chemfos site (Chapter 1). A review of the literature available at the time as well as approaches that were successfully implemented in other Western Cape rehabilitation projects such as the Du Toitskloof Pass and the Sishen–Saldanha railway line (Chapter 3), were considered. Previous studies on the west coast dunes at Blaauwberg had shown using Marram grass as a dune stabilizer was most successful. Marram grass was tested in trials alongside local grasses, such as Chaetobromus dregeanus and Ehrharta villosa, that showed potential but had not been formally evaluated. The environmental context of Chemfos (Chapter 2) as well as the Conceptual Rehabilitation Plan that considered the modified environment, soils and closure objectives of the mine, were reviewed to determine the most pressing rehabilitationrelated questions that required answers. This led to the final experimental design that was implemented mid-winter in 1996 (Chapter 5). The trials were implemented in the areas perceived to be the most difficult to rehabilitate, namely the mobile sands in the tailings dam and the exposed subsoil or mine floor areas. The use of brushwood together with specific plants and seeds appropriate for the use in either sandy soil or subsoil were evaluated in a variety of combinations and application densities to determine the most effective treatment combination at the minimum effective density. The best initial cover of the tailings dam were recorded in the Ammophila arenaria trials but the use of the local grass species Ehrharta villosa, performed better from year two onwards and was much cheaper to establish. On the subsoil, the trials where a cover of topsoil was used performed better than the combination trials. This indicated that topsoil placement on post-operational phase shaped subsoils during the mining operation to be the most desirable treatment. Initial results of the trials were used as a basis for developing the rehabilitation techniques that were rolled out across the Chemfos landscape. The approaches were refined as indications of trial responses became evident. Lessons learned were incorporated in the adaptive management approach that was followed and the rehabilitation techniques (Chapter 6) were continually re-evaluated and adjusted. This resulted in a significant step towards achieving the overall research objective of finding cost-effective approaches to rehabilitation. Components such as refinement of the seed collection and processing techniques (Chapter 7) where the post-harvest processing cost was significantly reduced by introducing specially designed drying racks. Processing techniques were adjusted to suit the different species, and a variety of mechanical processing options were explored. The scale of the Chemfos project led to the development of new techniques of manufacturing a smoke-derived germination stimulant (Chapter 8) since commercial availability of these products was very limited. The development of FireGrow assisted in the overall aim of reducing cost by increasing germination of seed in the rehabilitation sites using a very cost-effective smoke concentrate. Socio-economical aspects were considered during the implementation as well as the post-closure phases of the rehabilitation and BHPBilliton invested through the agency of the SAMANCOR Trust. This led to the development of livelihoods of the staff that remained in the area and that lived in the mine village. The demography of the population has changed over time in the Green Village as well as the skills that the inhabitants have developed. Thus, the new economic opportunities that were pursued have brought a new lease on life beyond the lifespan of the mine (Chapter 9) once the closure certificate had been issued.

The continuity of the menace of mercury (Hg) is due to the continuous production and use of Hg and Hg containing products. Toxicity is just an outfall of use and exposure. Anthropogenic activities such as coal combustion and artisanal and small-scale gold mining have led to increasing Hg contamination and is the major source of Hg pollution into the environment that needs to be remediated. This study aimed to assess the phytoextraction capability of sweet sorghum (Sorghum bicolor) under different fertiliser treatments in Hg-contaminated soil. The potted experiment in a controlled environment included control S. bicolor and three phytoremediation treatments, i.e., Hg only; the addition of 4:1 green compost and; the addition of 0.2% NPK fertiliser. There were conspicuous signs of Hg phytotoxicity in plants with Hg only, namely wilting, senescent, inhibition of growth, and photosynthesis. There was stunted growth, but healthy plants observed in the treatment with the addition of green compost towards the end (day 60) of exposure. However, S. bicolor grew well until the last day of exposure in the treatment with the addition of 0.2% NPK fertiliser. Thus, this treatment showed the most effective phytoextraction potential of S. bicolor in Hg-contaminated soil. The effectiveness of S. bicolor in reducing the level of mercury was best assessed in the Hg bioavailable concentration in the spiked soil in which the Hg + NPK treatment has the lowest (0.77 mg kg−1). That resulted in the highest uptake (84.31%) percentage of Hg concentration recorded in the treatment with the addition of 0.2% NPK fertiliser compared to the other two treatments. The results suggest that the proportion of phosphate in the NPK fertiliser used, plays a huge role in the phytoextraction of Hg in the contaminated soil by S. bicolor. The Translocation Factor (TF) and Bioconcentration Factor (BCF), although higher within Days 20 and 40, was greater than 1 at the end of the exposure period suggesting a high probability that Hg was significantly transferred to the aerial parts of the plants. This is regarded as typical hyperaccumulator plant species. While S. bicolor was able to reduce the level of Hg in all three treatments, Hg + NPK treatment gave overall best results in physiological growth, the uptake, and reducing the level of Hg bioavailable in the spiked soil in terms of the effectiveness of phytoremediation method. / Environmental Sciences / M. Sc. (Environmental Science)