This thesis examines the ecological consequences of sewage disposal in aquatic ecosystems. Sewage simultaneously represents a form of enrichment and a source of stress to a receiving system. Enrichment effects dominate when sewage loading does not exceed the capacity of the system to assimilate waste, as is presently the case in the St. Lawrence River. We developed a method to quantify the assimilation of sewage-derived organic matter by riverine biota, then used this method to examine the pathways by which sewage enhances secondary production in the St. Lawrence. We showed that the relative importance of dissolved nutrients and particulate organic matter to the river food web is to a large degree dictated by the physical and biological characteristics of the local environment. The effects of this enrichment on the receiving water community were also influenced by habitat characteristics. Analysis of body size distributions revealed that only the largest organisms had higher densities at enriched sites, and that the identity of these organisms depended on habitat structure. Densities of smaller organisms were controlled by a combination of habitat characteristics and feeding interactions. This pattern was consistent with food web models of top-down (consumer) control. At each trophic level, relatively invulnerable (large) prey achieved higher densities, whereas densities of more vulnerable (small) prey were controlled by their predators. Finally, we synthesized the ideas outlined above to predict how conditions in the St. Lawrence will change in the future as a result of lower water levels. More extensive macrophyte cover, slower current, and warmer temperatures in a shallower St. Lawrence will all enhance the ability of the system to physically retain and biologically process sewage nutrients, but will also increase the likelihood of negative effects such as anoxia.

No description available.

Biological invasions are among the leading causes of species diversity loss; however, the impacts of invasion are context-dependent and can vary with the local environment. The mechanisms governing variation in impact and their relationship to specific abiotic and biotic factors remain largely unexplored. Recent local declines in native unionid mussels have been attributed to the invasion of North American lakes and rivers by the Eurasian zebra mussel ( Dreissena polymorpha), as a result of intense fouling of unionid shells by zebra mussels. My research investigated the role of abiotic and biotic factors in mediating the impact of zebra mussels on native mussels. I examined the impact of zebra mussels on unionids in a habitat thought to be suboptimal for zebra mussels and compared this to the impact observed in other invaded habitats. A predictive model relating fouling intensity to local environmental variables (calcium concentration, sediment particle size) was developed, and a predator-exclusion experiment was conducted to investigate the role of predation in mediating fouling intensity. Overall, I found that two abiotic factors of the local environment were significant predictors of fouling intensity and that relationships used to predict the impact of zebra mussels could be extended to a broader range of habitats.

No description available.

The erosion of headwater wetlands in the Sand River catchment, in the lowveld of north-eastern South Africa has led to a focus on their rehabilitation, both for livelihood security for those that use them for subsistence agriculture, as well as for provision of streamflow regulation services for the Sand River itself. One such wetland, the Craigieburn-Manalana itself undergoing severe erosion was subject to technical rehabilitation using concrete weirs and gabion dams to stabilize the erosion gullies during 2007. Through a series of papers the research discussed in this thesis examined the response of the wetland?s hydrodynamics to the implementation of these measures. Through the installation of a network of hydrometric apparatus the research has shown that the wetlands hydrology is largely controlled by the presence of both horizontal and vertical clay aquicludes within a hydraulically conductive sandy matrix. The sequence of these aquicludes had allowed for artesian phreatic surface phenomena identified in a relatively hydrologically intact region of the wetland. The gully erosion had initiated hydraulic drawdown of the wetland?s water table leading to the desiccation of the system. The construction of a buttress weir within the erosion gully had restored the wetlands hydrodynamics to that typical of conditions upstream of a clay-plug. The research also explored the role that clay plays in terms of controlling the wetland?s hydro-geomorphic setting through geophysical analysis. A conceptual model was then derived that states that these wetlands are held in place by clay-plugs that form through clay illuviation from the hillslopes at regions of valley confinement. This has important implications for the connectivity of wetland process domains. The research also determined the inputs of surface and subsurface flows to the wetland and it was found through detailed examination of soil moisture responses and variably saturated soil physics modelling using the HYDRUS model, that the wetland is hydrologically connected to its contributing hillslope by threshold induced preferential flow pathways, via macropores, that only respond after specific antecedent soil moisture conditions are met. In addition, the thesis describes novel approaches to use information provided by soil scientists for the development of catchment hydrological models. It was shown that the use of this hydropedology information improved the low flow response function of the catchment model, ACRU. This development has important implications for up-scaling of catchment process domains, or hydrological response units by being able to generalize on hillslope hydrological responses based on configuration of their soil type elements. The research also undertook to examine the role that the wetlands play in catchment processes. It was found through water budgeting, supported by hydrological time-series, stable isotope analysis and the quantification of vegetation water use within the wetland and contributing catchment, that these wetlands do not augment baseflows during the dry season. Furthermore, it is only early on during the wet season that these systems may attenuate peak flows, thereafter they act as conduits for high storm flows. Similarities emanated from this research with previous hydrological studies of headwater wetland systems in southern Africa and these are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

This thesis describes the development of a decision support tool to be used in the operation of Vanderkloof Dam on the Orange River so that the supply of water to the lower Orange River can be optimised. The decision support tool is based on a hydrodynamic model that was customised to incorporate real time data recorded at several points on the river. By incorporating these data into the model the simulated flows are corrected to the actual flow conditions recorded on the river, thereby generating a best estimate of flow conditions at any given time. This information is then used as the initial conditions for forecast simulations to assess whether the discharge volumes and schedules from the dam satisfy the water demands of downstream users, some of which are 1400km or up to 8 weeks away. The various components of the decision support system, their functionality and their interaction are described. The details regarding the development of these components include: • The hydraulic model of the Orange River downstream of Vanderkloof Dam. The population and calibration of the model are described. • The modification of the code of the hydrodynamic engine so that real time recorded stage and flow data can be incorporated into the model • The development of a graphical user interface to facilitate the exchange of data between the real time network of flow gauging stations on the Orange River and the hydraulic model • The investigation into the effect of including the real time data on the simulated flows • Testing the effectiveness of the decision support system. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Water temperature is a critical factor affecting the abundance and richness of freshwater stream aquatic macroinvertebrate communities. Variable seasonal river temperature patterns are a critical factor in maintaining temporal segregation in aquatic invertebrate communities, allowing for resource partitioning and preventing competitive exclusions, while spatial differences in water temperatures permit zonation of species. This research investigated whether the degree of predictability in a stream’s water temperature profile may provide some indication of the degree of structure and functional predictability of macroinvertebrate communities. Quarterly aquatic macroinvertebrate sampling over a single year along the longitudinal axes of two river systems, Keurbooms River in the southern Cape, and the Kowie River in the Eastern Cape, were undertaken as the core component of this research. The two river systems shared similar ecoregions and profile zones, however were expected to differ in their thermal variability, based on the hydrological index and flow regimes for their respective quaternary catchments. Hourly water temperature data were collected at each sampling site from data loggers installed at five paired sites on each stream system. The aquatic biotopes sampled were in close proximity to the loggers. Multivariate analysis techniques were performed on the macroinvertebrate and water temperature data. Macroinvertebrate taxon richness was greater on the perennial Keurbooms than the non-perennial Kowie River where, on a seasonal basis, taxon richness increased from winter to autumn on both systems. Macroinvertebrate species turnover throughout the seasons was higher for sites having lower water temperature predictability values than sites with higher predictability values. This trend was more apparent on the Keurbooms with a less variable flow regime. Temporal species turnover differed between sites and streams, where reduced seasonal flows transformed the more dominant aquatic biotopes from stones-in-current into standing pools. Findings included aquatic macroinvertebrates responding typically in a predictable manner to changing conditions in their environment, where water temperature and flow varied. The findings of this research demonstrate that macroinvertebrate taxa do respond in a predictable manner to changes in their environment. This was particularly evident in relation to variability in water temperature and flow. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Winnipeg’s climate produces variable and extreme weather conditions, which can pose challenges for people wishing to spend more time outdoors. This practicum’s design builds on the Assiniboine River as a natural attractor and encourages people to spend more time outside. Relationships of architectural inside and outside are investigated and strategies to connect inside and outside are identified and applied in analysis of directly experienced projects. Those strategies together with a specific landscape vocabulary are the basis for the final design concept and examples. The design vocabulary and strategies are adapted to the quality of each site and support movement between the city and the river in all seasons.

Waters Edge began with the inspiration to be closer to water and progressed into exploring architecture within the inhabitation of the riverscape through the vehicle of an urban kayak station. A 1:1 scaled kayak was constructed to materialize the conceptual research and provide a means to understand the relationship between built form and water. The necessity of each line and material component in the kayak construction manifested itself into the making of the urban kayak station. Further research into the St. Johns rowing regatta and boat making enhanced the social aspect of revitalizing Winnipeg’s river culture. A series of architectural models and drawings were constructed to explore the conceptualizations of the research and multiple iterations of the project emerged. The research concludes with further exploration into the way we inhabit the riverscape.

CRISSP2D, a two-dimensional finite element model, was used to undertake a comprehensive hydrodynamic, thermodynamic, and dynamic ice study on the Red River near Netley Cut in order to determine the cut's effect on the local hydrodynamics and freeze-up processes. Open water hydrodynamic and thermodynamic models were developed, calibrated, and verified such that the measured data and simulation results were in acceptable agreement. These models were used as input to the dynamic ice model which was able to adequately predict ice thickness within the study area once the air-ice heat transfer coefficient was calibrated. The geometry of the dynamic ice model was subsequently altered to simulate the effects of sealing Netley Cut. The geometry change resulted in no noticeable difference in simulated ice thickness, but did affect the hydrodynamics within the study area. In particular, the water velocity in the Red River downstream of Netley Cut and water surface elevation upstream of Netley Cut both increased noticeably.