St. Lucia estuarine lake system has a history of episodic droughts and floods leading to a high variability in physico-chemical characteristics which may influence the community structure of nano- and microplankton that are the main primary energy synthesisers in aquatic systems. Originally, the St. Lucia estuary and the Mfolozi River shared the same mouth with the Mfolozi River acting as the main source of fresh water to the system and as stabiliser of the common inlet. Due to prolonged mouth closure from 2001-2012 and high evaporation rates, severe extended droughts and high salinities were experienced in 2001-2012.This project aimed to characterise community composition and biomass of nano-and microplankton (autotrophic and heterotrophic) under the varying and extreme physico-chemical conditions in order to characterize the energy basis of the planktonic food web in St. Lucia. Its main objectives were to compare and add onto Johnson’s (1977) list of phytoplankton taxa in the system, to estimate the biomass (carbon) of nano- and microplankton from cell counts and biovolume measurements, and lastly to understand and establish trends in the change in community structure of these organisms with the varying physico-chemical characteristics. Nano- and microplankton samples were collected monthly from October 2010 to September 2011 at three different sites: Lister’s Point, Charters Creek and the mouth representing the lakes and estuary Channel. Chlorophyll a and physico-chemical parameters were also measured in situ during collection. In the lab, samples were settled using the Utermöhl method and species were identified to at least genus level, counted and cell measurements taken under an inverted microscope for biovolume calculations and biomass thereof. Abundance in cells per liter and biomass (carbon) in pg/L was then analyzed from the counts. The nano-and microplankton groups recorded in the system were cyanobacteria, chlorophytes, cryptophytes, dinoflagellates, ciliates and diatoms. Seventy eight phytoplankton taxa were identified composed of 56 diatoms, eight green algae, one cryptophyte, seven cyanobacteria and six dinoflagellate taxa. Nineteen ciliate taxa were also found. Only 12 of the diatom taxa identified in this study were listed by Johnson (1977), none of the taxa in the other phytoplankton groups was listed by Johnson (1977). The Johnson (1977) study conducted in the system from 1975-1977 listed the phytoplankton taxa occurring at that time. There was no significant difference in the community composition, biovolume and biomass between seasons hence no seasonal trend however, there were significant differences in the nano- and microplankton community composition, biovolume and biomass at the three different sites of the system. Cyanobacteria were the main taxa in the northern embayments dominating in abundance, biovolume and biomass (biological variables), green algae and cryptophytes dominated in abundance, biovolume and biomass in the Channels while in South Lake, green algae dominated in abundance but diatoms dominated in biovolume and biomass. Ciliate biological variables were higher in the northern regions than in the other parts of the estuary. The absence or limited grazing pressure of ciliate predators in the northern region due to their inability to cope with the extreme salinities compared to the other parts of the system explains why the northern embayments had the highest abundance, biovolume and biomass of ciliates. Ciliates and heterotrophic dinoflagellates were the heterotrophs in this study. Autotrophic:heterotrophic biomass ratio was lowest in the northern regions as heterotrophs had a higher biomass there. This ratio was higher in the South Lake and the Channel. The lack of stratification and generally high turbidity in the system made the system unfavourable for dinoflagellate growth. The higher presence of ciliate predators in the South Lake and Channel probably accounts for the low heterotrophic biomass hence high autotrophic:heterotrophic biomass ratio in South Lake and the Channel. Nutrients were not limiting during this study and salinity was the main physico-chemical characteristic accounting for the differences in nano- and microplankton biological variables. The Cyanothece bloom in the northern region was primarily due to high salinities (>150) which also indicated unfavourable conditions for other plankton types. The high diatom biomass in the southern lake was due to low salinities (<28) which favoured their growth, whereas chlorophytes and cryptophytes dominated in the Channel mainly due to low turbidity (median of 11.4NTU) and fresh water input from the Mfolozi lowering salinities (<5). The South Lake and Channel thus had the highest available energy for higher trophic level organism since 1) diatoms and green algae are the most favoured food source for phytoplankton grazers while the cyanobacteria though most abundant are the least favoured food source leaving the northern lake with smaller energy source for higher trophic level organisms and 2) The low autotrophic:heterotrophic biomass ratio in the northern region leaves the region with a lower net carbon biomass than the other parts of the system with a higher autotrophic: heterotrophic biomass. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2013.

Phosphorus is an essential element since it controls primary productivity in aquatic ecosystems and its excess can lead to eutrophication in receiving systems. The aim of this project was to determine phosphorus distribution in biotic and abiotic nutrient pools of two KwaZulu-Natal estuaries. Samples of dissolved inorganic phosphorus (DIP), particulate phosphorus (PP), phytoplankton, microphytobenthos, zooplankton, macrozoobenthos and sediment were collected in the temporarily open/closed Mpenjati (MP) and permanently open Mlalazi Estuary (ML) during May (ML), September (MP) and November (ML+MP) using standard methods. Chlorophyll a concentrations as well as species richness, abundance and biomass of zooplankton and macrozoobenthos were analysed. Living and non living nutrient pools were analysed for phosphorus and were compared between stations, sampling sessions, estuaries and taxa. Zooplankton abundance and biomass in the Mlalazi Estuary was higher during May than November. In the Mpenjati Estuary highest zooplankton abundance and biomass was recorded during September than November. No significant differences were apparent in abundance (p = 0.217) and biomass (p = 0.974) of zooplankton between the two estuaries. Macrozoobenthos abundance and biomass in the Mlalazi Estuary was higher during May than November. In the Mpenjati Estuary macrozoobenthos abundance and biomass was higher during November than September. Significant differences in abundance (p = 0.003) and biomass (p = 0.020) were apparent between the estuaries. Sediment to a depth of 10 cm comprised the highest phosphorus biomass than any other nutrient pool in both Mlalazi (4871.1 mgP·m⁻² ± 5888.9 SD) and Mpenjati (2578.6 mgP·m⁻² ± 1828.0 SD) estuaries followed by DIP (120.5 mgP·m⁻² ± 177.7 SD and 5.9 mgP·m⁻² ± 6.1 SD respectively). In both estuaries, the lowest phosphorus biomass was contained in zooplankton with both estuaries containing zooplankton P biomass of 0.001 mgP·m⁻² ± 0.002 SD. Particulate phosphorus and DIP concentrations were higher in the upper reaches in both estuaries indicating that rivers were the main sources of this nutrient in these systems. The Mlalazi Estuary had higher nutrient levels than the Mpenjati Estuary. Such elevated nutrients can be enhanced by the continuous river flow into the permanently open estuary. In both estuaries, no significant differences were apparent in zooplankton and macrozoobenthos P content between different taxa. / M.Sc. University of KwaZulu-Natal, Durban 2013.

Microphytobenthos (MPB) generally dominates total autotrophic biomass in temporarily open/closed estuaries (TOCEs) of South Africa. A comparative study of MPB biomass was undertaken in two KwaZulu-Natal TOCEs, the Mdloti and the Mhlanga. Both estuaries receive different volumes of treated sewage waters. The Mdloti receives 8 ML.d-1, while the Mhlanga receives 20 ML.d-1, resulting in a capping flow of 0.092 and 0.23 m3.s-1, respectively. Through these effluents, eutrophication is enhanced and periods of mouth opening are also increased and prolonged, particularly at the Mhlanga. The aim of this study was to investigate fluctuations in MPB biomass in the Mdloti and the Mhlanga systems, with emphasis on freshwater flow and the alternation of closed and open phases. Sediment samples for MPB biomass were collected on a monthly basis, between March 2002 and March 2003, in the lower (mouth), middle, and upper (head) reaches of the two estuaries. MPB biomass ranged from 1.33 to 391 mg chI a m-2 and from 1.7 to 313 mg chI a m-2 in the Mdloti and the Mhlanga, respectively. A I-way ANOVA revealed no significant differences in MPB chI a concentrations between the two estuaries for the entire data set (Fl, 76 =1.48, P > 0.05). At the Mdloti, MPB biomass varied considerably, with values ranging from 1.33 to 131 mg chI a m-2 during the open phase, and from 18 to 391 mg chI a m-2 during the closed phase. A Mann-Whitney U test confirmed the high significance of these differences between open and closed phases (U= 29, P < 0.001). At the Mhlanga, MPB biomass ranged from 7.0 to 313 mg chI a m-2 during the open phase, and from 1.7 to 267 mg chI a m-2 during the closed phase. Unlike what was observed at the Mdloti, the higher MPB values at the Mhlanga were not always associated with the closed mouth state. In relation to key physico-chemical and biological factors, grazing pressure exerted by the zooplankton community appeared to have played a major role in controlling MPB biomass. Zooplankton biomass was consistently and positively correlated to MPB biomass throughout the study period both at the Mdloti (r = 0040, P < 0.001) and at the Mhlanga (r = 0.33, p < 0.05). Unlike what was shown in previous studies, light attenuation was not significantly correlated with MPB biomass during the period ofthe study, either at the Mdloti or the Mhlanga. These results show that the opening and closing of the mouth play a key role on the MPB biomass of both estuaries. The Mdloti seems to function as a typical TOCE, with prolonged open and closed phases. The Mhlanga, on the other hand, lacks a prolonged closed phase. This, in turn, affects its entire trophic structure and functioning. / Thesis (M.Sc.)-University of KwaZulu- Natal, 2004.

Estuaries are dynamic features of a coastline whose sediments are influenced by riverine and marine processes. Periodic events such as floods, as well as variations in mouth status, greatly affect the energy levels within an estuary and subsequently the amount of sediment erosion and deposition that takes place. Concurrently, pollutants are transported and deposited into estuaries and can reside in the sediments for many years. The estuaries of the eThekwini Municipality in KwaZulu-Natal, South Africa, are exposed to a variety of pollutants; however with the expanding industrial sector within this region, metal contamination is of concern. This study investigates the sedimentology and geochemical variations of six estuaries within the municipality namely, the uTongati, uMdloti, uMgeni, Isipingo and uMbokodweni estuaries as well as the Durban Harbour. To determine the spatial variations in estuarine sedimentology, sediment cores were collected longitudinal to the estuary axis. The core samples were analysed for sediment colour, texture and organic matter content. To assess the geochemical variations, core samples were analysed for Zn, Cu, Cr, Ni, Pb, As, Fe, Al, Ca, S, P, Mg, Mn, Cd and V concentrations. Some samples were also carbon dated to provide a temporal aspect to the sediment and geochemical variations. Descriptive and graphic techniques were used to examine the sedimentology within the estuaries; and the geochemical data was analysed with the use of multivariate statistics. Additionally, pollution indices and sediment quality guidelines were utilized to assess the pollution levels within the sediments. The results indicated that lower energy environments caused by protracted mouth closures in the uMdloti and Isipingo estuaries accounted for large amassing of fines. In contrast, the accumulation of mixed coarse and fine sediments in the uTongati and uMgeni estuaries was an indication of high fluvial flows and open mouth conditions. All carbon dated ages for all estuaries were greater than 700 years which may be attributed to a combination of scouring effects from past and recent flood events and also possibly due to the deposition of re-worked older sediments from upstream. Low metal concentrations were found within the sediments of all estuaries, and the presence of fines and organic matter governed their concentration variations with depth. The uMgeni and uMbokodweni estuaries which are located immediately downstream of industrial and urban areas, were found to contain relatively higher concentrations of elements Pb, Cu, As and Ni. These metals showed high enrichment within the sediments; however actual concentrations were below sediment quality guideline levels. General pollution levels within all estuaries were very low, and can be attributed to the climatic influences within this region which has a ‘cleansing’ effect on the estuarine environments in removing contaminants. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2014.

The St Lucia estuarine system, Africa’s largest estuarine lake, is characterised by cyclic changes from hypersaline to oligo/mesohaline conditions in response to alternations between drought and wetter than average years. In addition, St Lucia also experiences stochastic disturbances, such as flooding events that rapidly decrease salinity levels. Due to their sessile and slow moving nature, bivalves are particularly vulnerable to rapid or prolonged changes in the physico-chemical environment. The recent freshwater deprivation crisis that prevailed for the last decade resulted in a significant loss in bivalve species richness within the system. An annotated and illustrated bivalve census revealed the occurrence of twenty-four species within St Lucia between the years 1925 and 2011. However, only six species were recorded during the most recent survey in March 2011. The infaunal razor clam, Solen cylindraceus, and the epifaunal brackwater mussel, Brachidontes virgiliae, are currently the dominant bivalve species within St Lucia. This study, therefore, aimed to record the species richness of bivalves found in Lake St Lucia and to investigate key biological aspects of the two dominant bivalve taxa within the system, under different salinity regimes. Experiments revealed that S. cylindraceus can tolerate salinities between 15 and 65, while B. virgiliae prefers salinity levels ranging from freshwater to 20. The varying tolerance limits, therefore, dictate the distribution of these species during different climatic conditions within the estuarine lake. During wet periods, S. cylindraceus is restricted to the northern reaches, unable to tolerate the oligohaline conditions present in the rest of the system. Conversely, B. virgiliae, often restricted to the Narrows, becomes ubiquitous throughout the system under such conditions. Solen cylindraceus can reach a maximum length of 95 mm. However, in the St Lucia estuarine system, specimens seldom exceed a length of 55 mm, probably because prevailing/re-occurring harsh conditions prevent them from reaching maximum size. In situ measurements of this species also revealed less growth during the first year of life than for the same species in different systems. While B. virgiliae is substantially smaller than S. cylindraceus, the high densities that this species is able to attain makes it an important grazer with the potential to have significant feeding impacts on the local phytoplankton biomass. Results showed that in localised areas, B. virgiliae populations may consume up to eight times the available phytoplankton biomass. These key bivalve species are strongly influenced by the fluctuation in climatic conditions from wet to dry phases. Thus, understanding the effects that climatic shifts have on key estuarine species is essential, as flood and drought events are predicted to increase in frequency, intensity and duration as a result of global climate change. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2014.

South African estuaries have high biodiversity value and provide many benefits to society, including food, real estate, a place for recreation and economic enterprise. However, they are facing growing human pressures such as urban encroachment, development in river catchments and interference in hydrological cycles. This dissertation provides an exploratory study of the environmental history of the Mgeni River Estuary, KwaZulu-Natal in an attempt to improve the understanding of the forces that drive environmental change. Through the application of the techniques and methodologies of environmental history, it explores the dynamics, characteristics and impacts of human interaction with the Mgeni River Estuary over time. It focuses on the emergence of a capitalist! industrial society in the twentieth century as this period has been characterised by the most significant environmental alteration and degradation. With the aid of the techniques and methodologies employed, the study highlights a complexity of natural and human events that have altered the estuary over time. Comparative analysis of aerial photographs between 1937 and 1996 reveals that physical changes to the estuary were linked to prevalent social and economic activities. The study describes cultural beliefs, modes of resource use and the political economy as significant and interwoven factors that facilitate environmentally intrusive activities. The study has provided insights into the complexity of factors that influence the rate and extent of change of an estuarine system. It concludes that to improve the understanding of the causes of environmental change, it is necessary to look further than the physical impacts on the environment to the attitudes and beliefs that underlie them. While the solutions to the problems facing the Mgeni River Estuary are not easily at hand, such analysis should assist policy makers and managers in finding a way to initiate more sustainable estuarine development in the future. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

The Isipingo River and Estuary system located in the province of KwaZulu-Natal, although relatively small, has been subjected to the impacts of intense development within the catchment. The catchment is characterized by informal and formal dwellings and intensive industrial activities in the lower catchment and in close proximity to the estuary. Significant modifications to the hydrology of the system has occurred as a result of the diversion of the Umlazi River (which previously merged with the Isipingo River at the estuary mouth), canalization of the lower portion of the Isipingo River flowing through the Prospecton Industrial Area and the development of the Diversion Works system (to regulate flows to the lower Isipingo River), removal of riparian vegetation, encroachment onto the river and estuarine floodplain, and land reclamation through the infilling of wetlands all of which has culminated in a deterioration of the functionality and health of this system. The main aspects of this study focus on water and sediment quality, material flux between the estuary and the sea and the management of the system. The water quality variables covered as part of this dissertation include physical, chemical (nutrients and heavy metals) and microbiological (faecal coliforms) components. The water quality of the river and estuary presents a risk to human health and the concentrations of heavy metals generally exceeded the South African Water Quality Guidelines that prescribes target levels, implying potential negative impacts to aquatic health. The Isipingo system exhibited signs of eutrophication with phosphorus concentrations in excess of the target level to prevent eutrophication. Excessive water hyacinth growth was visible during most of the field surveys. A geochemical assessment of heavy metals in surface sediments of the river and estuary was also undertaken. The results indicate that although the presence of several metals were undetectable at certain river sites, the concentrations of those heavy metals present increased in a longitudinal direction from the river to the estuary. The contamination factor analysis for all metals indicated low contamination except for selenium. The riverine sites yielded moderate enrichment by some heavy metals in both seasons. The degree of contamination for each site with the exclusion of selenium was low. The inclusion of selenium in the assessment raises the estuary to a considerably contaminated status in the wet season. The analysis suggests that the enrichment of the system by selenium is due to an anthropogenic source. The Geo-accumulation Index places the sediment in an overall unpolluted category. The study conducted on the net exchange of heavy metals and nutrients between the Isipingo Estuary and the adjacent marine environment (i.e. Indian Ocean) demonstrates that significant quantities of the suite of heavy metal analysed are exported on an annual basis while copper, nickel and zinc are imported into the estuary. Significant quantities of ammonia and nitrates are exported annually from the Isipingo Estuary while a net annual import of phosphorous is observed. The variation in the quantity and concentration of nutrients exported during the seasons may be attributed to anthropogenic source. The import of nutrients from marine sources can accumulate in the estuary and contribute to eutrophication of the Isipingo Estuary. This study also demonstrated that although the ebb flow has a much longer duration than the flood flow, the flood velocities observed were generally greater than the ebb velocities. The final part of this research identifies other environmental problems experienced in the Isipingo catchment. The following issues are identified as directly or indirectly contributing to stress and deterioration of the water quality of the Isipingo system: reduction in water quantity, poor water quality, moderate enriched sediment, loss of habitat integrity, species diversity and invasive alien vegetation and uncontrolled solid waste. A Water Quality Management Plan including management objectives, strategies and action plans to address the direct and indirect factors influencing the system are proposed. A water quality monitoring program is also proposed for the Isipingo River and Estuary. The adoption and execution of the water quality management plan and monitoring program will assist in the prevention of further degradation of the system and will be a stepping stone toward improvement. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2013.