The aim of this study was to identify the algal genera found in the different freshwater bodies on Marion Island, to relate the presence or absence of the genera to the chemistry of the water bodies and to group the genera according to their limno-chemical preferences. The Island's freshwater algal genera were also compared with genera found on other Southern Ocean islands. The major factors influencing the chemical composition of the freshwaters of the island are the surrounding ocean and the manuring of seals and seabirds. The Western and Southern lakelets and wallows had higher mean conductivity values than most of the other water bodies. Eastern Inland lakelets, crater lakes and glacial lakes had low ion and nutrient concentrations, since they are mainly situated inland, away from bird or seal colonies. The chemical composition of wallows was influenced by manuring of seals and seabirds. The freshwaters are acidic and lakelets tend to be more acidic than glacial lakes. The lentic waters were more acidic than the stream. In total, 106 genera, mainly belonging to Chlorophyta (60 genera; 56% of total) and Cyanophyta (29 genera; 27% of total), were found in the freshwaters on the island. Other algal divisions found were Chrysophyta (7 genera), Euglenophyta (4 genera), Pyrrophyta (2 genera) and Xanthophyta (4 genera). Mean number of genera per sample ranged from 8 (in wallows) to 16 (in Eastern Inland lakelets). Filamentous algae were present in all the samples. Abundant green algae were Cosmarium, Klebsormidium, Mougeotia and Oedogonium. The most common cyanobacteria were Lyngbya and Chroococcus. The filamentous yellow-green alga, Tribonema, was also common. There were distinct differences in the algal composition between the southern, western and northern lakelets and the lakelets on the eastern side of the island. Sixty percent of the algal genera were present in waters with low conductivity values. Trichodesmium, Sphaerocystis and Tolypothrix occurred in freshwater bodies with higher conductivity values. Variance analysis showed that 87 of the 106 genera were less likely to occur in nitrogen and phosphate containing waters. Chlamydomonas, Prasiola, Spirogyra Trachelomonas, Tribonema, Ulothrix and Xanthidium were among the genera commonly found in nitrogen and phosphate containing waters. Diversity (number of genera per sample) was negatively correlated with conductivity, PO4-P, NH4-N and NO3-N. Diversity declined significantly with increasing salinity and eutrophication. Genera likely to occur in acidic waters include Binuclearia, Chlamydomonas, Chroococcus, Cosmarium, Klebsormidium, Microspora, Oedogonium, Oocystis, Prasiola, Scenedesmus, Staurastrum, Stigeoclonium, Tetrastrum, Ulothrix, Lyngbya, Synura and Tribonema. Marion Island’s algal flora shows a high affinity with that of Îles Kerguelen and Crozet, both located in the same biogeographical province (South Indian Ocean Province) of the sub-Antarctic than Marion Island, and a lesser affinity with islands in other sub-Antarctic provinces. Algal genera were grouped according to their limno-chemistry preferences. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.

The aim of this study was to identify the algal genera found in the different freshwater bodies on Marion Island, to relate the presence or absence of the genera to the chemistry of the water bodies and to group the genera according to their limno-chemical preferences. The Island's freshwater algal genera were also compared with genera found on other Southern Ocean islands. The major factors influencing the chemical composition of the freshwaters of the island are the surrounding ocean and the manuring of seals and seabirds. The Western and Southern lakelets and wallows had higher mean conductivity values than most of the other water bodies. Eastern Inland lakelets, crater lakes and glacial lakes had low ion and nutrient concentrations, since they are mainly situated inland, away from bird or seal colonies. The chemical composition of wallows was influenced by manuring of seals and seabirds. The freshwaters are acidic and lakelets tend to be more acidic than glacial lakes. The lentic waters were more acidic than the stream. In total, 106 genera, mainly belonging to Chlorophyta (60 genera; 56% of total) and Cyanophyta (29 genera; 27% of total), were found in the freshwaters on the island. Other algal divisions found were Chrysophyta (7 genera), Euglenophyta (4 genera), Pyrrophyta (2 genera) and Xanthophyta (4 genera). Mean number of genera per sample ranged from 8 (in wallows) to 16 (in Eastern Inland lakelets). Filamentous algae were present in all the samples. Abundant green algae were Cosmarium, Klebsormidium, Mougeotia and Oedogonium. The most common cyanobacteria were Lyngbya and Chroococcus. The filamentous yellow-green alga, Tribonema, was also common. There were distinct differences in the algal composition between the southern, western and northern lakelets and the lakelets on the eastern side of the island. Sixty percent of the algal genera were present in waters with low conductivity values. Trichodesmium, Sphaerocystis and Tolypothrix occurred in freshwater bodies with higher conductivity values. Variance analysis showed that 87 of the 106 genera were less likely to occur in nitrogen and phosphate containing waters. Chlamydomonas, Prasiola, Spirogyra Trachelomonas, Tribonema, Ulothrix and Xanthidium were among the genera commonly found in nitrogen and phosphate containing waters. Diversity (number of genera per sample) was negatively correlated with conductivity, PO4-P, NH4-N and NO3-N. Diversity declined significantly with increasing salinity and eutrophication. Genera likely to occur in acidic waters include Binuclearia, Chlamydomonas, Chroococcus, Cosmarium, Klebsormidium, Microspora, Oedogonium, Oocystis, Prasiola, Scenedesmus, Staurastrum, Stigeoclonium, Tetrastrum, Ulothrix, Lyngbya, Synura and Tribonema. Marion Island’s algal flora shows a high affinity with that of Îles Kerguelen and Crozet, both located in the same biogeographical province (South Indian Ocean Province) of the sub-Antarctic than Marion Island, and a lesser affinity with islands in other sub-Antarctic provinces. Algal genera were grouped according to their limno-chemistry preferences. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012.

MENVSC (Climatology) / Department of Geography and Geo-Information Sciences / Subtropical anticyclones locate and modulate weather and climate over subtropical belts for both the Northern and Southern Hemispheres. This study investigates the spatio-temporal variability of the Mascarene High over the South Indian Ocean on (anomalous) weather and climate over southern Africa at intraseasonal, seasonal, interannual, multidecadal and event time-scales. The Mascarene High is located 25-35°S, 40-110°E, playing a vital role in day-to-day weather and climate patterns conditions over southern Africa. Spatio-temporal characteristics of the Mascarene High investigated in this study span the period 1985-2014 and 2071-2100, using NCEP-NCAR reanalysis datasets for present-day climate observations and the Conformal-Cubic Atmospheric Model (CCAM) for future projections. The Mascarene High is analysed using mean sea level pressure (MSLP) extracted from ECMWF ERA-interim monthly reanalysis data. The Mascarene High is also subjected to Principal Components Analysis, depicting eastern displacements of the weather system to be dominant for weather and climate fluctuations over southern Africa. The Mascarene High migrates south (north) during austral summer (winter) and is centred over the eastern Indian Ocean in summer in connection with the Indian Ocean Subtropical Dipole. Event scale analysis is also employed for investigating Mascarene High blocking and induced anomalous weather. Mascarene High blocking leads to anomalous rainfall events over southern Africa associated with tropical cyclones, cut-off lows and cloud bands. There is also a vital geographical variability of the Mascarene High development, distribution and movement in the South Indian Ocean at the different time-scales. Projections of the Mascarene High indicate a shift in mean location as a result of future expansion and intensification. This projected expansion and intensification is expected to shift tropical cyclone trajectories equatorward, with the baroclinic structure of cold fronts expected to shift poleward affecting changes in the weather and climate of southern Africa. This finding is important as it projects changes in weather and climate conditions over southern Africa in a changing climate due to increased greenhouse gas emissions.