Wetlands have long been recognised as enhancing the quality of inflowing waters, particularly regarding the plant macronutrients nitrogen and phosphorus. Any research into non-limiting solutes has largely been of a 'black box' nature, with no insights into mechanism of retention presented. Research in the Okavango Delta, Botswana and preliminary work in the uMkhuze Wetland System, South Africa has identified retention of large amounts of non-limiting solutes within these wetland systems. Chemical sedimentation in the Okavango accounts for 360 000 tonnes per year, while a rough mass balance in the uMkhuze Wetland System suggested retention on a scale of 16 000 tonnes per year. The Yengweni and Totweni Drainage Lines are north-south oriented systems that, together with the uMkhuze River floodplain, were selected to investigate chemical retention in the uMkhuze Wetland System. These drainage lines were once tributaries of the uMkhuze River that have been dammed at their southern ends by alluvial deposition on the uMkhuze River floodplain to form tributary valley lakes. Considering seasonal variations in groundwater levels in combination with conductivity, sites of solute concentration were revealed in the groundwater. The use of chloride as a concentration tracer has indicated that solutes are progressively depleted in the groundwater under the influence of a concentration mechanism, with silicate minerals and calcite attaining saturation. Groundwater chemistry and hydrological factors have highlighted the southern Yengweni and floodplain regions as active sites of solute concentration. In these areas, groundwater elevations are variable, which is mirrored by variation in groundwater chemistry. Although elevated solute concentrations do occur elsewhere, the seasonal variation is less marked. The search for solute sinks in the uMkhuze Wetland System also considered the sediment of the wetland system as a possible sink. Elevated solute concentrations in the groundwater could be linked to the accumulation of minerals in the soil, suggesting precipitation of minerals by saturation under a concentration process. In tho southern Yengweni and floodplain regions, concentrated groundwater bodies were linked to high concentrations of minerals in the soil, including neoformed montmorillonite, and calcite deposits. Other sites of chemical concentration in the groundwater in the northern Yengweni and Totweni Drainage Lines have produced little modification of the reworked marine sands on which the wetland is founded. Processes in the southern Yengweni and floodplain regions are clearly more efficient in removing solutes from the wetland surface water and immobilising them in the soil of the drainage line than is happening in the Totweni and northern Yengweni regions. Transpiration by vegetation seems to be the major factor driving chemical sedimentation in this subtropical system, and as such vegetation in this wetland system is not the passive factor it is often assumed to be. The vegetation of the wetland is itself initiating and perpetuating the retention of chemicals in the system. Hierarchical patch dynamics in combination with the theory of thresholds, derived from geomorphology, is useful for placing chemical sedimentation in wetlands into a spatiotemporal framework that increases understanding of the process, and allows identification of sites where chemical sedimentation is likely to occur in wetlands. There are a number of thresholds that define chemical sedimentation driven by evapotranspiration in the uMkhuze Wetland System, which may be considered at increasing spatiotemporal scales from the microscale of seconds within a limited section of the groundwater, to the macroscale thousands of years at the landscape scale of the wetland system. With increasing scale, the effects of the transformations at each hierarchical level have corresponding increasing influence on the structure and function of the wetland system. The initial threshold is surpassed once concentration products of evapotranspiration are retained to some degree within the wetland system, due to increased residence times of groundwater on modification of the hydrological regime from discharge to recharge. Increased residence times allow the products of seasonal concentration to persist beyond the timescale of seasons. The second threshold is the saturation and precipitation of mineral phases that accumulate within the soil profile. With sufficient accumulation of chemical sediments, the physical properties of the sediment are modified, which reduces the velocity of water flow in the soil (Threshold 3). This has implications for hydrological flows between the surface water and groundwater systems. Threshold 4 is attained once the sediment is modified to such a degree that the chemical sediments act as an aquitard, such that surface water and groundwater may be effectively separated. Extrinsic factors influencing the process of chemical sedimentation, such as the atmospheric water demand, chemical composition and volume of inflowing waters, as well as the nature and density of vegetation, may indicate the potential of a system to sequester chemical sediments but cannot predict their occurrence completely, except maybe at the extremes of semi-arid and arid systems. It is the local and intrinsic factors of hydrological flows, their chemical composition and nature of clastic sediments that will govern residence times of water in the system, and therefore the location, nature and extent of chemical sedimentation. Furthermore, chemical sedimentation driven by evapotranspiration is not limited by sediment type as are adsorption and complexation reactions, which are dependent on the availability of active sites, nor by chemical composition of inflowing waters as this factor simply dictates the suite of minerals produced. Therefore, chemical sedimentation in wetlands is expected in a wide range of settings from temperate to arid, with varied substrates and hydrological regimes. The large-scale removal and retention of solutes within wetland soil has system-wide implications for wetland structure and functioning. The ramifications of chemical evolution of the groundwater and soil extend from influencing the distribution of plants and animals, to geomorphological implications of accumulating chemical sediments, as well as off-site effects including water quality enhancement of water available to downstream systems and users. An understanding of the process of chemical sedimentation in wetlands may inform good management to protect this vital function of wetlands, particularly with increasing development and industrialisation pressures in many areas. Extensive chemical sedimentation has been discovered in both the Okavango Delta, Botswana by Ellery, McCarthy and colleagues and through this study in the uMkhuze Wetland System, with the proposed driving force being transpiration. Vegetation induced chemical sedimentation is a hitherto unknown, although seemingly important component, of chemical processing in tropical and subtropical wetlands, and under certain conditions, even in temperate wetlands. This insight into chemical transformations in wetland systems adds a further dimension to the accepted model of chemical cycling. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2008.

The wetlands on the Eastern Shores of Lake St Lucia are primarily groundwater fed and exhibit a variety of hydrological regimes that give rise to a high degree of habitat and species diversity. Hydrologically unstable systems experience ecophasal shifts that can disrupt an established steady state within the wetland ecosystem. Communities of both plants and animals can accordingly disintegrate into more or less isolated populations, open to re-invasion by preceding or "new" species when conditions change again. Given the ephemeral and episodic nature of much of the surface water on the Eastern Shores, ecological dynamics of this type are likely. Fish and aquatic invertebrates were sampled from a number of routine and other sites between May 2002 and April 2003. Measurements of various environmental and abiotic factors (including pH, ionic conductivity and dissolved oxygen levels) were taken with each sample in order to establish relationships between environmental changes and the assemblages of aquatic fauna occurring within the Eastern Shores wetlands. Conditions on the Eastern Shores during the study were somewhat anomalous, as the region experienced drought conditions during this period. The Eastern Shores wetlands support a diversity of aquatic fauna, including at least four species of freshwater fish listed as rare or threatened by the IUCN. The aquatic organisms existing within this dynamic system exhibited changes in abundance and distribution that reflected the spatial and temporal changes in their environment. The relationships between aquatic organisms and their environment were complex, with assemblages being affected by combinations of changing environmental and habitat variables as well as other factors such as the environmental stability of habitats and stochastic effects. Given the complex nature of these interactions, aquatic macrofauna on the Eastern Shores are likely to be best conserved through the preservation a heterogeneous mix of wetland habitats, maintaining the diversity of wetland structure and function on the Eastern Shores that can facilitate an element of lottery in the development and structure in biotic assemblages. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

The aim of this study was to describe the plant communities within the eastern portion of the Mkuze Wetland, including only those systems that have a substantial input of water from the Mbazwane Stream, and to determine environmental factors that control distribution. The Mbazwane Wetland has a catchment of reworked sandy marine sediments, and its gradient is very shallow, such that water moving downstream through this system is free of suspended sediment and is clear. In addition, it has low conductivity suggesting a low solute load. A total of nine communities were identified in the study, based on the TWINSPAN cluster analysis. These are: Ficus trichopodalScleria angusta Swamp Forest Community; Rubus rigidus Disturbed Swamp Forest; Phragmites australis/Ficus trichopoda Precursor Swamp Forest; Typha capenis/Pycreus mundii/Leersia hexandra Marsh Community; Phragmites australis/Cladium mariscus/Ficus verruculosa Swamp Community; Cyperus papyrus Swamp Community; Echinochloa pyramidalis Floodplain Community; Ischaemum fasciculatum/Centella asiatica Floodplain Community; Paspalum distichum Floodplain Community. These communities can be divided into three broad groups, swamp forest, emergent herbaceous swamp/marsh and grassland floodplain communities. One of the main environmental variables influencing distribution was duration and depth of flooding, which separated the permanently flooded swamp and emergent swamp/marsh communities from the seasonally/ periodically inundated floodplain communities. Environmental variables that account for further division of the communities within these two groups, appear to be disturbances from fire and substratum differences related to sediment deposition from the Mkuze River, which enters the lower Mbazwane Wetland from the west. The permanently flooded swamp forest communities, are largely restricted to the northern parts of the study area, while the emergent swamp/ marsh communities, are restricted to the southern part of the study area. The swamp forest community is fringed to the west by an extremely high and steep dune, while the swamp/marsh communities are fringed to the west by much lower and more gently sloping dunes. It is suggested here that wildfires in conjunction with topography influence the distribution of these two groups of communities. An analysis of diurnal variation in temperature in the winter months (June - August) for winds (greater than l.0m/s) reveals that winds blowing from the west to north-west are associated with extremely high temperatures that persist during the day and well into the night. These are berg wind conditions that have been strongly linked to the desiccation of vegetation and promoting its susceptibility to burning in wildfires, and it is during these conditions that fires are most likely to occur in the study area. Swamp forest is situated in areas that are protected from direct exposure to these winds by the high, steep dune immediately to the west. These are thus likely to be naturally protected from fire. In contrast the herbaceous swamp/marsh communities are not protected from wind or fire by a similar topographic feature. Mature swamp forests were restricted to these 'berg wind shadow' areas, where there is complete protection from fire. Precursor and disturbed swamp forests occur where they are less protected and thus are infrequently exposed to fire. The distribution of the permanently flooded swamp/marsh communities in the areas exposed to fire appears to be related to the input of nutrients. The Cyperus papyrus Swamp Community was rooted in clay rich peat in the area around the Mkuze Delta that receives an input of clay from the Mkuze River during very high floods. In contrast, the Phragmites australis/Cladium mariscuslLeersia hexandra Swamp Community was rooted in peat with low ash content, as there is little or no input of clay from the Mkuze River, even during high floods. The seasonally/periodically- flooded communities included the Echinochloa pyramidalis Floodplain Community, the Ischaemum fasciculatum/Centella asiatica Floodplain Community and the Paspalum distichum Floodplain Community. The Echinochloa pyramidalis Floodplain Community was restricted to seasonally flooded areas receiving an input of clastic sediment from the Mkuze River during high floods, while the other floodplain communities occurred in areas receiving water from the relatively sediment free Mbazwane Stream. The distribution of these two communities appears to be influenced by the duration of inundation, with the lschaemum fasciculatum/Centella asiatica Floodplain Community being at higher elevation and therefore less frequently flooded than the Paspalum distichum Floodplain Community. / Thesis (M.Sc.)-University of Natal, Durban, 2000.

Hlatikulu Vlei, situated in the foothills of the Natal Drakensberg, is one of the priority wetlands in KwaZulu-Natal, occupying an area of 733 Hectares. The importance of Hlatikulu Vlei lies in its functions to store water, regulate stream flow and attenuate floods, as well as to provide suitable habitat for wildlife and grazing for livestock. Hlatikulu Vlei is a threatened system and has suffered the effects of human mismanagement. Forty-nine percent of the vlei has been classified as disturbed or destroyed, mainly due to the construction of two large dams and past drainage of vlei to facilitate pasture planting. The effects of grazing and fire on the plant communities has been considerably less. Vegetation communities at Hlatikulu Vlei have similarities with those at Ntabamhlope Vlei. The main plant communities present at Hlatikulu Vlei are: vlei grassland, sege-meadows, bulrushes and reedswamp. Species compositions of the mixed sedge and grass sedge-meadow community have a notably higher species diversity than similar communities sampled at Ntabamhlope Vlei and the mires at Highmoor. Soil type and moisture content are shown to be the most significant environmental factors determining the distribution of plant communities and species within the vlei. A wetland re-establishment and rehabilitation programme in the Hlatikulu Crane and Wetland Sanctuary has been effective in allowing many wetland plants to become reestablished. The sanctuary communities bear greater similarity to the sedge and rush sedge-meadow community, than the mixed sedge and grass sedge-meadow communities that were originally present. This is also reflected in the seed bank. All three Southern African crane species (Blue, Wattled and Crowned Crane) and fourteen species of waterfowl have been recorded in the Hlatikulu Crane and Wetland Sanctuary since the wetland rehabilitation programme. The waterfowl play a role in the dispersal of seeds into the sanctuary, particularly those of Schoenoplectus decipiens and Eleocharis dregeana and are in part responsible for the return of certain wetland plants to the sanctuary. The flooding of soils, the fluctuating water level and the soil type related to hummocks and to channels are shown to be responsible for the location of Cyperus denudatus, Arundinella nepalensis and Aristida junciformis in differing positions in the channels and on the hummocks and are also responsible for the maintenance and functioning of the hummocks and channels. Seed banks on the hummocks are similar to seed banks in the channels, however the extant vegetation on the hummocks is distinctly different to that in the channels. Certain species represented in the channel seed bank are being excluded from surviving to maturity. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.