Investigations were made examining the relationships between gastropod species richness and abundance across 20 phosphate and 20 natural lakes in Central Florida. In additional to lake category, age of phosphate lakes was used to determine if phosphate lakes ever approximate natural lakes. Additional physical, chemical, and biological parameters, including chlorophyll a, Ca, secchi, phosphorous, conductance, fish predation, and recreational lake use were investigated in order to determine if they affected gastropods with lake age. Comparisons were also made between gastropod species richness and average abundance and two groups of dominant vegetation categories: Panicum, a structurally complex macrophyte, and Typha, a less structurally complex macrophyte. After phosphate mining operations are completed, Florida state regulations require the establishment of ecologically viable habitat (created lakes) which reflects the properties of regional natural lakes including vegetation structure, littoral zone, bank slope, and lake depth. The littoral zone is part of the mandated structure of the lake, and is of considerable importance to the uptake, storage, transformation and release of nutrients. Within the littoral zone, gastropods are a critical link in the food web with implications for the long term structure and function of a lake. They are known for their close associations with macrophytes and are common environmental indicators since they have limited mobility, high diversity, are well studied, are representative of their habitat type and have a widespread geographic range. They are also an important food sources for many predators in aquatic environments, include migratory waterfowl and game fish. Gastropod species richness and abundance data were collected via standard net sweep methodology. Abundance was presented in catch per unit effort, therefore all abundance data were averages. Initial comparisons between gastropod species richness and average abundance yielded no significant differences between natural and phosphate lakes. However, when age was applied as a covariate, there was a significant difference between lake age as a continuous variable in species richness comparisons. Additionally, categorical comparisons between lakes older or younger than 30 years indicated significantly higher species richness and average abundance of gastropods in lakes phosphate lakes older than 30 years. Physical and chemical properties of the lakes did not appear to influence gastropod populations between lakes of different ages. Fish predation interactions did not indicate any significant influence either. However, the presence of boat ramps did indicate a positive relationship between average gastropod abundance and species richness and recreational lake use. Littoral zone macrophyte comparisons between dominant vegetation Typha and Panicum indicated a significantly positive relationship between gastropod species richness and average abundance in older phosphate lakes dominated by the more structurally complex Panicum macrophytes. Confidence in the Typha and Panicum results was confounded by lack of access to younger, Typha dominated, phosphate lakes. An increase in sample size for younger Typha lakes, with additional site access, may further support these findings.

This report contains the results of some ecological and systematic studies on the diatoms from the Vaal Dam catchment area in the Transvaal, and the Bloukrans River in the Eastern Cape Province. In Part 1 the effects of high concentrations of nitrogen were studied in relation to the composition of the diatom associations. Water samples from four stations on the Bloukrans River were analysed chemically at certain intervals during the months of April and August 1967. Diatom samples collected from these stations at the beginning and end of each of these sampling periods were subjected to a "Thomasson Analysis" to determine the relative densities of the various species in the diatom associations. A statistical analysis of the results reflected a poor but positive correlation between the two variables, i.e. high numbers of nitrogen heterotrophic Nitzschiae were correlated with high concentrations of nitrogen, while low numbers were correlated with low concentrations. Part 2 presents the results of the ecological studies on the diatom associations of the Vaal Dam Catchment Area. In this section the diatom associations from each sampling point or station were subjected to a "Thomasson Analysis" to determine the relative densities of the different species in the associations. Employing already known correlations between environment and association, the results of this analysis were discussed and the ecological conditions for each sampling station were assessed. The associations were similar in composition over the entire catchment area, and indicated on the whole water of good quality. Points of pollution were detected, but were generally localised and the effects of the pollution were soon removed. Only the Waterval River showed evidence of more constant pollution. The associations provided evidence for some seasonal variation in their composition. Finally in Part 3 the systematics and taxonomy of the diatoms in the Vaal Dam catchment area are discussed. References are made to the original and more recent descriptions of each species found in this study, and a list of synonyms is given wherever 'possible. Comments on the systematics, taxonomy and autecology of each species are given, and the distribution of the species in South Africa and the Vaal Dam catchment area is discussed. A number of species, varieties and forms have been recorded for the first time in South Africa. During the course of this study 20 species have been described as new to science; the descriptions of some have been published, while the descriptions of the others will be published formally in the future. All species described as new or having interesting features are illustrated in the plates.

The biological integrity of aquatic ecosystems has become threatened by the effects of high nutrient loads, inorganic and organic chemicals. The effect of these xenobiotics needs to be investigated by the application of biotests in whole effluent toxicity testing and biomarkers in active biomonitoring. Whole effluent toxicity (WET) testing determines the toxicity/effect of whole effluent on aquatic organisms. Sub-lethal effects can be determined by analysing the levels of subcellular/physiological indicators/enzymes in aquatic organisms exposed to in situ conditions. The procedure used for in situ assessments was active biomonitoring (ABM). The aim of this study was to assess the instream health of a known contaminated system (Rietvlei Wetland System, Gauteng, South Africa) using WET and ABM methodologies. Three sites in the Rietvlei Wetland System were selected and sampling was undertaken during high flow (April 2003) and low flow (August 2003) periods. The ABM sampling protocol involved the deployment of aquatic molluscs (Melanoides tuberculata) and fish (Oreochromis mossambicus) for a period of four weeks at the sites. Following the four week exposure period the organisms were transported back to the laboratory and the following biomarkers were assessed: ethoxyresorufin o-deethylase (EROD), acetylcholine esterase (AChE) and metallothione (MT). Water samples were also collected for WET testing during the low flow period, since this was the only period where mortality was observed in the ABM organisms. Standard WET protocols were used to assess the toxicity of the water from the three sites. These protocols were: 96 h Poecilia reticulata lethality test, 48 h Daphnia pulex lethality test and 72 h Selenastrum capricorutum growth inhibition test. In addition the same biomarker analyses that were done on the ABM organisms were carried out on WET exposed D. pulex and P. reticulata. The WET testing and ABM indicated highest toxicity at Sites 1 and 3. Algal growth inhibition test showed highest stimulation of algal growth at Site 2 and inhibition at Site 3. Sites 1 and 2 showed signs of contamination by organophosphates and carbamates due to elevated AChE and reduced EROD. However there were no significant differences in AChE activity between fish tested in the 96h toxicity test and those used in ABM. Very low AChE activity was recorded in D. pulex. Snails also had lower AChE activity when compared to the exposed fish species. Metallothionein content was higher in field-exposed fish than those used in WET, however both assessment protocols indicated that Site 3 was affected the greatest by metals. Snails exhibited higher MT content than fish and D. pulex showed no MT activity. There were no significant differences in MT content between the sites. Acetylcholine esterase appears to be a relevant means of investigating biological effects of many neurotoxic contaminants on aquatic habitats and trophic levels. Metallothionein content is a good indicator of toxicity due to heavy metals for active biomonitoring as well as the WET test. Ethoxyresorufin-O-deethylase is a more difficult biomarker to work with since it shows no differences in activity between control and exposed organisms. The EROD assay does not detect very low levels of EROD induction. Acetylecholinesterase and MT are the recommended biomarker assays for the detection of sublethal responses in the WET laboratory toxicity test. The AChE activities and MT exhibit comparable results in both ABM and WET assessment protocols. In future studies WET testing needs to be complimented with a suite biomarker analyses to determine the type of pollutants in a system and sufficiently describe the pollution status of a system. / Dr. V. Wepener

The biological integrity of aquatic ecosystems has become threatened by the effects of eutrophication, acidification as well as increased organic and inorganic chemical loads. It is necessary to identify the effects of xenobiotics before the onset of death in an exposed organism or deteriorating changes at population level. Biochemical and physiological indicators such as enzymes and stress proteins could be used as a valuable tool for detecting chemical exposure and evaluating their effects on aquatic organisms. The use of selected enzymes in different organs/tissue was evaluated as possible indicators of stress in fish, in their natural environment as well as under controlled laboratory conditions. During the field assessment of enzymes it was found that selected enzymes could be used as indicators of pollution between high flow and low flow seasons when pollution conditions are more concentrated. However, the various enzymes are non-specific indicators of stress and could therefore, be influenced by environmental changes, handling and struggling in the nets. Exposure to sub-lethal and lethal iron concentrations caused significant differences between the levels of enzymes in exposed and control Oreochromis mossambicus, indicating that the use of enzymes under controlled laboratory conditions, toxicity testing is more effective. The demand for sensitive and specific biological assays needed to be satisfied. Heat shock induction after sub-lethal iron exposure was investigated in the reproductive organs/gonads of O. mossambicus. After the refinement of the standard protocol for the assessment of Heat shock protein 70 (HSP 70) it was found that HSP 70 induction are more intense in male individuals than in female individuals. Higher protein concentrations were also found in female reproduction organs possibly due to the presence of vitellogenin. The use of HSP 70 as a diagnostic tool to monitor cell damage after sub-lethal iron exposure was less effective due to several factors including (1) the selection of the target organ, (2) the different stages of sexual development between individuals, (3) the selection of the exposure toxicant and (4) the presence of another stress protein in female gonads. Most researchers use the Atomic Absorption Spectrophotometry (AAS) method to determine the metal content in fish organs/tissues. During this research it was attempted to find a more time effective, rapid, less hazardous and more economic method to determine metal content in fish organs/tissues. After comparison between the AAS method and Scanning Electron Microscope Energy Dispersive X-ray (SEM-EDX) microanalyses the AAS method was found to be the most effective method to determine metal content in fish organs/tissues. SEM-EDX microanalyses techniques need more refined sample preparation, calibration and operation skills. / Prof. J.H.J Van Vuren

Philosophiae Doctor - PhD / Results from this study enables a better understanding of groundwater surface water interactions in the TMG, particularly regarding aquatic ecosystems. It has also highlighted the necessity to do proper impact assessments before proceeding with bulk abstraction from this important aquifer. The results also demonstrated the importance of differentiating between real groundwater and non-groundwater discharge contributions to surface hydrology and where these interface areas are located. / South Africa

The trophodynamic implications of reduced freshwater inflow on the zooplankton of eastern Cape estuaries was investigated by a comparison of the community composition and standing stocks, grazing rates and food resources of zooplankton in two systems, the Kariega and the Great Fish estuaries, which are subject to contrasting freshwater inflow. The climate of South Africa is semi-arid, and the low rainfall, coupled with high evaporative loss, result in the region having one of the lowest conversions of rainfall to run-off in the world. In addition, many of the major rivers are extensively impounded, consequently, estuaries often experience prolonged periods of zero or reduced freshwater inflow. The amount of freshwater available for estuarine management in the future is expected to decline as the demand for domestic, agricultural and industrial use increases. The influence of climate, tidal amplitude and wave action are essentially constant, consequently, the individual characteristics of an estuary are determined largely by the indirect influences of catchment size and regulation. Estuaries along the eastern Cape coast range from negative hypersaline systems, to positive systems in which a salinity gradient is well established. The Kariega estuary is a homogeneous marine estuary as a result of minimal freshwater inflow, whereas the Great Fish estuary receives sustained freshwater inflow and is partially-stratified. The quality and quantity of particulate food resources for suspension-feeders depended to a large extent on the allochthonous import of material associated with freshwater inflow. Nutrients, rather than light penetration of the watercolumn are the major factor limiting phytoplankton standing stocks. In the Kariega estuary, phytoplankton standing stocks were low (up to 1.0 μg l⁻¹) and the estuary is classified as oligotrophic. Correlation analyses indicated that lower quality detritus, originating from fringing macrophytes, may contribute substantially to suspended particulate organic material. Phytoplankton food resources were considerably higher in the Great Fish estuary (up to 21.8 μg ⁻¹) which is classified as mesotrophic/eutrophic, and correlation analyses indicated that phytoplankton comprised the dominant fraction of the particulate organic material. Although this suggested that the organic material was of a higher quality, the seston was "masked" by a higher suspended inorganic load. Consequently, the organic fraction comprised between 13 and 22% of total particulate material in the Great Fish estuary, compared with between 20 and 39% in the Kariega estuary. Food resources demonstrated a fairly uniform distribution along the length of the Kariega estuary and exhibited a slight seasonal increase during warmer months. By contrast, the point source influence of freshwater inflow resulted in a spatial gradient of food resources in the Great Fish estuary with higher values recorded towards the upper reaches. There was evidence that higher concentrations of particulate material in the upper reaches are also a consequence of hydrodynamic trapping. There was no marked seasonal pattern in the availability of food resources which were generally elevated in response to sporadic pulses of freshwater inflow. Tidal currents were responsible for elevating suspended food resources by re-suspension of material from the sediments. This effect was probably of greater importance in the Kariega estuary where food resources were generally limiting. In the Kariega estuary, the zooplankton community was dominated by calanoid copepods of the genera Acartia and Pseudodiaptomus. However, in the Great Fish estuary, the community was dominated by the mysid Mesopodopsis siabberi, and the calanoid P. hessei. Community biomass generally reflected the trophic status of the estuary. The mean seasonal biomass recorded in the Kariega estuary was 38 mg m⁻³ compared with 1597 mg m⁻³ in the Great Fish estuary. Greater spatial variability in community biomass was evident in the Great Fish estuary, partly in response to the food resource gradient, but also due to the inability of the mysid shrimps, which dominated the community biomass, to penetrate the lower salinity water of the upper reaches. Zooplankton in the Kariega estuary demonstrated a seasonal pattern of abundance whereas in the Great Fish estuary, community biomass was elevated in response to sporadic pulses of freshwater inflow. Grazing rates, measured in situ using a modified Gliwicz-Haney chamber, indicated that the zooplankton communities were capable of "clearing" substantial proportions of the watercolumn at certain times of the year. The pattern of grazing pressure over a diel cycle was examined in relation to the diel vertical migration movements of the zooplankton. Higher nighttime grazing rates were generally associated with the greater abundance of zooplankton resulting from the movement of zooplankton into the watercolumn after dusk, and their return to the sediments at dawn. Seasonal estimates of diel grazing pressure, extrapolated from daytime and nighttime feeding rates, indicated that the zooplankton "cleared" up to 40% of the watercolumn in a day in the Kariega estuary, and up to 120% d⁻¹ in the Great Fish estuary. However, values of around 25% d⁻¹ in the Kariega estuary, and 50 to 80% d⁻¹ in the Great Fish estuary, were not uncommon. Multiple regression analyses were used in an attempt to explain the influence of environmental factors on the variation in in situ grazing rates. These attempts were largely unsuccessful and the possible reasons, as well as recommended improvements to the methods used, are discussed. Seston concentration in the estuaries was highly variable as a result of the effects of tidal re-suspension and freshwater inflow. Consequently, further laboratory-based experiments were carried out to examine the influence of seston concentration on the filtration rates of the dominant calanoid copepods. Results indicated that some of the unexplained variability in the community filtration rates may be attributed to differences in species-specific response to changes in seston concentration.

Rising temperatures associated with climate change will alter the fundamental physiological processes of most ectothermic species. Drastic changes in catabolic and anabolic reaction rates exert strong effects on growth, reproduction, and consumption rates that cascade up through all levels of the biological hierarchy. This dissertation determined how climate warming might alter the important relationship between plants and insect herbivores, as mediated through changes in herbivore physiology. Consumption and fitness increased with temperature for almost all consumers. However, all consumers also exhibited a critical temperature, beyond which consumption declined rapidly through metabolism continued to increase. This mismatch in metabolic demands and energy intake reduced consumer fitness at high temperatures. Furthermore, increased metabolic nitrogen demand can induce nitrogen limitation in insect herbivores at high temperatures. These basic physiological changes can modify the way herbivores interact with plants in a number of ways. For example, the Japanese beetle, Popillia japonica, altered its feeding behavior on numerous host plant species, depending on host plant quality. Unfortunately, the effects of temperature on plant-herbivore interactions will be difficult to predict, as there was no predictable relationship between consumption and temperature across numerous plant-herbivore pairs. Finally, rising temperatures disrupt insect herbivore control of plant fitness, thereby altering one of the most important components of plant-herbivore interactions. Thus, climate change will fundamentally change the nature of plant-herbivore interactions in the future.

Estuaries are dynamic on many spatial and temporal scales. Distinguishing effects of unpredictable events from cyclical patterns can be challenging but important to predict the influence of press and pulse drivers in the face of climate change. Diatom assemblages respond rapidly to changing environmental conditions and characterize change on multiple time scales. The goals of this research were to 1) characterize diatom assemblages in the Charlotte Harbor watershed, their relationships with water quality parameters, and how they change in response to climate; and 2) use assemblages in sediment cores to interpret past climate changes and tropical cyclone activity. Diatom assemblages had strong relationships with salinity and nutrient concentrations, and a quantitative tool was developed to reconstruct past values of these parameters. Assemblages were stable between the wet and dry seasons, and were more similar to each other than to assemblages found following a tropical cyclone. Diatom assemblages following the storm showed a decrease in dispersion among sites, a pattern that was consistent on different spatial scales but may depend on hydrological management regimes. Analysis of sediment cores from two southwest Florida estuaries showed that locally-developed diatom inference models can be applied with caution on regional scales. Large-scale climate changes were suggested by environmental reconstructions in both estuaries, but with slightly different temporal pacing. Estimates of salinity and nutrient concentrations suggested that major hydrological patterns changed at approximately 5.5 and 3 kyrs BP. A highly temporally-resolved sediment core from Charlotte Harbor provided evidence for past changes that correspond with known climate records. Diatom assemblages had significant relationships with the three-year average index values of the Atlantic Multidecadal Oscillation and the El Niño Southern Oscillation. Assemblages that predicted low salinity and high total phosphorus also had the lowest dispersion and corresponded with some major storms in the known record, which together may provide a proxy for evidence of severe storms in the paleoecological record.

M.Sc. / Biomarkers are responses in living organisms that signify exposure to harmful substances. The use of biomarkers enables researchers to detect toxicity at suborganismal level. It can thus be used as an early warning of chronic pollution. This project employs biomarkers in preliminary field research to assess aquatic ecosystem health. The indigenous freshwater fish Oreochromis mossambicus and Labeo umbratus are used as test organisms. Mature fish are collected at polluted and unpolluted sites. Blood, brain- and liver tissue is removed and analysed. Laboratory evaluation involves the exposure of juvenile Oreochromis mossambicus to a variety of toxic chemicals in a static system to determine biomarker responses. The biomarkers investigated include acetylcholinesterase, which is inhibited by organophosphate and carbamate pesticides and pyruvate kinase, which is a ratelimiting enzyme of glycolysis. Lactate dehydrogenase is used as biomarker for muscle tissue damage and glucose-6-phosphate dehydrogenase is a key regulatory enzyme of the pentose-phosphate shunt. Osmotic anion and cation concentrations are measured to determine stress on the regulation of water- and osmotic balance. Although results from the field study is variable, some biomarkers show potential to be included in a suite of biomarkers for biomonitoring, together with other biological, physical and chemical measures. Applying techniques to assess a suite of biomarkers in key organisms, produces a more accurate reflection of ecosystem health. Exposure studies with juvenile fish produced extremely variable and unreliable results. Many repetitions of each exposure will be necessary to determine significant deviations in biomarker responses from the normal range.

No description available.