Browsing by Author "Dallas, Helen Fiona"

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    Biological assessment of tropical riverine systems using aquatic macroinvertebrates in Tanzania, East Africa
    (2014) Kaaya, Lulu Tunu; Day, Jenny; Dallas, Helen Fiona
    In Tanzania, and in East Africa in general, bioassessment methods for monitoring and assessing riverine ecosystems are not yet in place. This thesis describes the development of a macroinvertebrate-based bioassessment method for assessing the degree of anthropogenic disturbance in Tanzanian rivers. The hypotheses that, 'macroinvertebrate assemblages reflect disturbance in river systems'; 'rivers with similar abiotic features have similar macroinvertebrate assemblages'; and 'spatio-temporal variation in macroinvertebrate assemblages influence bioassessment', are tested. Macroinvertebrate and environmental data were collected from the Pangani, Rufiji and Wami-Ruvu basins. Univariate analyses; constrained and un-constrained ordinations and a linear response model were used to test the hypotheses. Five important bioassessment aspects were investigated. A set of 20 criteria for screening reference sites was established and used to identify and distinguish between reference and test sites in the study area. A two-level hierarchical framework for classifying homogenous river types was developed and validated. Three river types were classified: Pangani highland uplands, central eastern Africa uplands and central eastern Africa lowlands, each with two sub-Groups. A macroinvertebrate-based biotic index, the Tanzanian River Scoring System (TARISS), was established for monitoring and assessing anthropogenically induced disturbance in Tanzanian rivers. TARISS has three metrics; number of taxa, TARISS score and average score per taxon (ASPT) for measuring disturbance. Spatio-temporal variations in macroinvertebrate taxa, assemblages and TARISS metrics were examined. Spatial variation within river types was driven by catchment characteristics such as geographical location, geology, altitude and local characteristics such as active channel width, proportions of boulder, cobble and sand on the bottom, influenced reference conditions in all three river types. Temporal variations were significant in the central eastern Africa lowlands, with higher TARISS metrics in wet than in dry periods. Biological and physico-chemical reference conditions were identified for each river type and sub-Group. Guidelines for interpreting TARISS data were established for the validated sub-Groups. In conclusion, TARISS proven to be reliable in detecting anthropogenic disturbance in Tanzanian rivers and is recommended as a national bioassessment method.
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    Effects of water temperature on life history traits of selected South African Aquatic insects: implications for the ecological reserve
    (2014) Ross-Gillespie, Vere; Dallas, Helen Fiona; Day, Jenny; Picker, Mike
    Life-history studies have informed all areas of aquatic ecological research, whilst also providing information relevant for conservation and management of aquatic systems. Given the large research gap that has existed in this regard for Southern Hemisphere lotic systems, there has been an urgent need to gather such data if effective management policies are to be implemented regionally, especially in the face of ongoing development, anthropogenic impacts, and global climate change. Furthermore, there has been a growing awareness of the need to incorporate thermal guidelines into legislation regarding environmental flows and associated water management plans. In South Africa radical new legislation introduced in 1996 resulted in rivers and aquatic ecosystems being given a right to water of their own- essentially environmental flows, required to protect the aquatic ecosystems associated with the water resource, that are determined separately for all or part of any significant water resource. This water, including both the quantity and quality, is referred to as the "Ecological Reserve." Baseline information on the relationship between temperature and life-history patterns of aquatic insects is required to inform the incorporation of thermal guidelines in the Ecological Reserve determination process. Assuming such information can be gathered, a problem arises as to how the data can be interpreted and incorporated into management guidelines. For instance if representatives of widespread species occurring throughout a country are collected from a single location (say perhaps a single province in South Africa) and then analysed in terms of their thermal limits for growth – would these limits hold true for that same species where it occurs elsewhere? Intra-specific variability, cryptic species and broader phylogenetic constraints all influence the thermal limits of species and need to be considered when examining thermal influences on life-history patterns. This thesis aimed to test the overarching hypothesis that while the life-history traits of aquatic insects could be constrained to some degree by their evolutionary history, they would also be impacted by thermal and hydrological regimes, inducing a degree of plasticity in their life cycles. This hypothesis was tested by examining the key life-history traits of three representative taxa of aquatic insect, namely Lestagella penicillata (Ephemeroptera), Aphanicercella spp. (Plecoptera) and Chimarra ambulans (Trichoptera), and how they are driven by environmental and genetic factors in six rivers situated in the south-western Cape Province of South Africa.
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    An evaluation of SASS (South African scoring system) as a tool for the rapid bioassessment of water quality
    (1995) Dallas, Helen Fiona; Day, Jenny
    The South African Scoring System (SASS) is a rapid bioassessment technique based on one component of riverine biotas, the benthic macroinvertebrates. Each taxon is assigned a tolerance/sensitivity score, which are summed to provide a Total Score. The Average Score per Taxon (ASPT) is calculated by dividing this Total Score by the number of taxa. This study was undertaken to evaluate the SASS technique as a tool for the assessment of water quality. Three study-sites, which differed in water quality, in the south-western Cape were selected for a detailed investigation into sample variability and replication of two methods of biological assessment, namely quantitative box-sampling and SASS. The ability of each method to differentiate between these sites was determined. The more general application of SASS in the south-western Cape was examined at forty nine sites and potential problems associated with SASS, namely biotope availability, temporal variability and longitudinal changes were investigated. A minimum of twelve and four quantitative samples is needed to ensure collection of 95% or 75% of benthic macroinvertebrate taxa respectively. Sampling within a single biotope component, such as a "riffle" or "run" would reduce the number of samples needed. A minimum of four and two SASS samples is needed to ensure collection of 95% or 75% of the taxa respectively. This technique is however designed such that only one sample is taken per site. The Total Score that one sample would produce as a percentage of the Total Score from 20 samples, were 28% , 59% and 45% for Sites 1, 2 and 3 respectively. Total Score increases with increasing sampling effort, whilst ASPT is relatively unaffected by sampling effort. ASPT should therefore be used in interpretation of scores. Variability, as determined by both quantitative sampling and rapid bioassessment, was greatest at the least impacted site. Such sites should be more intensively sampled, either by increasing the number of box- samples taken, or by increasing the time period for SASS sampling.
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    Spatial and temporal heterogeneity in lotic systems : implications for defining reference conditions for macroinvertebrates
    (2001) Dallas, Helen Fiona; Day, Jenny
    Spatial and temporal heterogeneity of lotic systems was examined by assessing variability in macroinbertebrate assemblages in two geographic regions, the Western Cape and Mpumalanga, in South Africa. Assemblages were assessed using the South African Scoring System (SASS), a rapid bioassessment method. The implication of spatial variability at regional, subregional and habitat levels, and temporal variability for defining reference conditions for macroinvertebrates was evaluated.
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    Stream invertebrates and water temperature : evaluating thermal tolerances in the Cape floristic region (South Africa) - implications of climate change
    (2009) Ketley, Zoma Anne; Picker, Mike; Reed, Cecile C; Dallas, Helen Fiona
    Temperature is an important environmental variable for aquatic invertebrates as it affects their development, reproduction and survival. Temperature also affects the abundance and distribution of individuals in a stream or river. Stream temperatures are affected by human impacts which include not only impacts such as pollution, abstraction of water and the removal of riparian vegetation, but also the affects of climate change. In the Western Cape Province, South Africa, it is predicted that air temperatures will increase and winter rainfall will decrease. This in turn will affect water availability and water temperatures in streams and rivers. Thermally sensitive species are threatened by increases in water temperature, but currently very little information exists on the thermal tolerances of aquatic invertebrates in South Africa. In order to rectify this problem baseline data on thermal tolerances of aquatic species needs to be collected, together with stream temperature and associated invertebrate community data. An attempt was made to collect some of these much needed data in the Western Cape Province. Two methods, namely Critical Thermal Maxima (CTM) and LT₅₀ experiments, were used to determine the thermal tolerances for a range of aquatic insect nymph species from the southwest fynbos bioregion and the south coast fynbos bioregion. The results from the experiments provided information on the relative thermal sensitivities of the species. Overall Aphanicerca capensis (form C and undescribed form), Notonemouridae ranked as the most thermally sensitive for both experiments. The A. capensis species complex (and possible other notonemourid stoneflies) may potentially be used as an indicator of changing stream temperatures in the Western Cape Province. To rapidly determine thermal sensitivities the CTM experiments are recommended rather than the more time consuming LT₅₀ experiments as the relative thermal tolerance for the species tested ranked the same for both experiments. It is suggested that LT₅₀ experiments of longer duration be investigated in order to compare the experiments to naturally-occurring thermal stress. Stream temperature and community composition data were collected from Window Gorge Stream, on Table Mountain, to provide baseline data for future monitoring and understanding of potential changes in thermal profiles. Temperature loggers were placed at six sites along the stream. Stream temperatures were fairly low but the stream ran dry during the late summer months (February through to April/May). From the community composition data collected the highest diversity was found during the winter months, as expected. The community composition did change down the length of the stream, with the species composition found near the source being quite different to that of the species composition found lower down the mountain. Temperature and associated oxygen saturation were two important variables related to the community composition down the length of the stream. It is important that experimental data be combined with field data, enabling field sampling to focus on the collection of information on the abundance of the thermally sensitive species (e.g. A. capensis species complex). Recorded stream temperatures also provide reference conditions for the species tested in the laboratory. Climate change is likely to have an affect not only on stream temperatures but also on water availability, which will both influence stream communities and ecosystems and it is important to understand what these potential effects might be.
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    The thermal tolerances and preferences of native fishes in the Cape Floristic Region: towards understanding the effect of climate change on native fish species
    (2017) Reizenberg, Jody-Lee; Dallas, Helen Fiona; Shelton, Jeremy Mark; Reed, Cecile C
    Global climate change models indicate that a rise in temperature and reduction in rainfall in the Western Cape Province of South Africa is inevitable and unavoidable. Within the Western Cape lies the Cape Floristic Region (CFR); a biodiversity hotspot with high levels of endemism. This includes its freshwater fish assemblage. Whereas the current greatest threats to native fish biodiversity are habitat degradation and invasion by non-native species, predicted climate change is likely to further impact fish communities negatively. As a master abiotic variable in aquatic ecosystems; temperature influences the fitness, behaviour, and life-histories of aquatic biota. Thermal alteration may therefore affect sensitive fish species. The upper thermal limit, determined via the critical thermal method, has been validated as a measure of thermal sensitivity. To better understand the impacts of climate change on the native fish of the CFR, upper thermal limits (critical thermal maxima/CTmax) were determined for seven native species of freshwater fish. Thermal preferences were also determined for five of these species using the acute gradient tank approach to elucidate thermal habitat preferences. Species that were identified by the IUCN as vulnerable, endangered, or critically endangered were selected from the four main families of native fish in the CFR (Anabantidae, Austroglanidae, Cyprinidae, and Galaxiidae), from four Rivers. Overall, Cape galaxias (Galaxias zebratus), Breede River redfin (Pseudobarbus burchelli), Berg River redfin (Pseudobarbus burgi), Clanwilliam redfin (Pseudobarbus calidus), and fiery redfin (Pseudobarbus phlegethon) were found to be most sensitive to increased temperature (CTmax= 29.8-32.7⁰C). Clanwilliam rock-catfish (Austroglanis gilli) and Cape kurper (Sandelia capensis) were found to be moderately sensitive (CTmax= 33.0-35.3⁰C). Similar trends were found using the thermal preference approach as CTmax and thermal preference were found to correlate well. The results were related to in-situ water temperature, which influenced both parameters. Thermal tolerances and preferences of all the native species exceed that of invasive salmonids (Onchorynchus mykiss and Salmo trutta). However, non-native centrarchids (Micropterus spp.) are more thermally tolerant, indicating an increase in threat by warm adapted non-natives. These data suggest that species interactions and distributions are likely to undergo substantial changes in response to elevated water temperature.