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Thesis (M. Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 62-71).

M.Sc. / The main objective of this study was to perform active biomonitoring in the Rietlvlei Wetland System. Active biomonitoring, which can be defined as “the translocation of organisms from one place to another and quantifying their biochemical, physiological and/or organismal responses for the purpose of water quality monitoring” (De Kock and Kramer, 1994), has several advantages over the chemical monitoring system. Effluents often are complex and poorly characterized mixtures of a large number of chemicals. A combination of many chemicals being present in very small amounts (even below detection limits) can have a substantial impact on organisms, and a chemical-based approach may not identify the source of pollution nor will effect of synergism or antagonism be taken into account (Smolders et al., 2003). A suite of biomarkers of oxidative stress and histopathology were investigated in the fish Oreochromis mossambicus and the mollusk Melanoides tuberculata. The organisms were bred under laboratory conditions. They were deployed during the high-flow and low-flow periods, in cages at three sites down the flow gradient of the Rietvlei wetland system, to determine spatial and temporal variations in biomarker responses and general water chemistry in the system. The oxidative stress biomarkers analyzed were catalase (CAT), superoxide dismutase (SOD), peroxidase (GPx), as well as levels of reduced glutathione (GSH) and lipid peroxidation as malondialdehyde (MDA). There was evidence of presence of chemicals inducing oxidative stress in the organisms as indicated by the high levels of MDA, GSH and GPx. Induction of CAT and SOD was not substantial due to possible inhibitory factors. This study established that organism transplantation is a feasible strategy for biomonitoring. Overall, no distinct variations were observed in the spatial and temporal comparisons in all the biomarker responses. The findings of this investigation also provide a basis for further investigation into the application of these biomarkers in ecological risk assessment. / Dr. V. Wepener

PhD. (Chemistry) / This project assessed the toxicity of double-walled carbon nanotubes to three aquatic organisms belonging to different trophic levels, namely Pseudokirchneriella subcapitata (algae), Daphnia pulex (macro-invertebrate) and Poecilia reticulata (fish). Prior to the toxicity testing, the dry DWCNTs were characterised using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. Dynamic light scattering was used to characterise DWCNT suspensions. Natural water parameters such as increased ionic strength (Ca2+ and Na+) and increased humic acid affected the agglomeration potential of DWCNTs in aquatic medium. Increased ionic strength increased the agglomeration of DWCNTs while humic acid decreased agglomeration. The study explored the lethal/effective concentrations and sublethal effects of DWCNTs on the three organisms. The LC50/EC50 of DWCNTs for the three organisms differed in order of magnitude with D. pulex being the most sensitive and P. reticulata being the least sensitive. The LC50 for D. pulex was 2.81 and 4.45 mg/L for pristine and oxidised DWCNTs, respectively. Pseudokirchneriella subcapitata had an average EC50 of 10.01 mg/L and 10.93 mg/L for pristine and oxidised DWCNTs, respectively. Poecilia reticulata had an LC50 of 113.64 mg/L and 214.0 mg/L for pristine and oxidised DWCNTs, respectively. Exploring the effects of natural water parameters such as humic acid and ionic strength revealed that the acute toxicity of DWCNTs to D. pulex and P. reticulata was increased with increasing humic acid concentrations in exposure media, but increased ionic strength decreased the toxicity of both pristine and oxidised DWCNTs. However, these water parameters all decreased the toxicity of DWCNTs to P. subcapitata. The acute toxicity of DWCNTs was found to be directly linked to their agglomeration state in aquatic systems. Humic acid decreased the hydrodynamic sizes of DWCNT agglomerates making the engineered nanomatrials (ENMs) more available to the organisms while the cations increased the hydrodynamic sizes of DWCNT agglomerates, thereby reducing the probability of interactions with organisms. Time-based survival plots revealed that for P. reticulata and P. subcapitata, there were steady mortality/growth inhibitions throughout the duration of the exposures. For D. pulex, however, the plots revealed that there was a high initial die-off, whereafter mortalities proceeded at different rates. An assessment of whether DWCNTs cause oxidative stress in the three organisms revealed that DWCNTs caused significantly high oxidative stress in D. pulex and P. reticulata but not in P. subcapitata. In D. pulex and P. reticulata, DWCNTs were found to also cause DNA damage. The sublethal toxicity of DWCNTs was affected differently by the humic acid and increased cation concentration in exposure experiments. The sublethal effects were linked to the mode of interaction between DWCNTs and organisms. In P. subcapitata, the interaction was mainly physical with DWCNTs entrapping the algal cells in agglomerates and depriving the algal cells of light for normal photosynthesis to take place. For the other two organisms, the interaction was through intestinal cells as the organisms ingested DWCNTs and through accumulation of nanotubes on the exterior or organisms. The intestinal cell/DWCNT interaction resulted in the excessive generation of reactive oxygen species (ROS) and led to the death of the organism. Humic acid induced the highest antioxidant responses in both D. pulex and P. reticulata and this led to increased DNA damage in both organisms. Increased ionic strengths induced increased antioxidant responses at some DWCNT concentrations but the DNA damage was not significantly increased. These results suggested that with humic acid, the ROS production was excessive and sustained and had an effect on the DNA. The ROS production in increased ionic strengths was not excessive and was not prolonged, reducing their impact on DNA. The use of three organisms to assess the toxicity of DWCNTs provided comprehensive information on the potential effects of these ENMs in the aquatic food chain. Moreover, a multi-tier approach provided information on the potential effect of DWCNTs on populations at sublethal concentrations.

The impacts of Invasive Non-Native Species (INNS) are well documented, and INNS management is widely considered one of top threats to global biodiversity and ecosystem function. The American signal crayfish, Pacifastacus leniusculus, is a destructive invader of freshwater ecosystems. In Scotland, this species currently has a restricted distribution. Despite the known impacts and high rates of dispersal, little is being done to manage populations that threaten to spread into Scotland's economically important catchments. One barrier to action on the management of signal crayfish is uncertainty over the implementation and efficacy of control methods. Capture-mark-recapture analysis was used to estimate the size- and season-specific capture probabilities of three traditional and two novel mechanical removal methods. By simulating the effect of harvest with these removal methods on a density-independent population model, a range of optimal seasonal combinations of removal methods were derived. Little empirical evidence exists in compensatory density-dependent dynamics in signal crayfish. I found that the probability of an individual cannibalising was affected by its size and also the density of conspecifics around it. I trialled a seasonally optimal combination of removal methods in two populations, manipulating sections of stream with different crayfish removal intensities, and tracked the movements of marked individuals. There was a high rate of dispersal (33%) that was influenced by the quality of the patch it was leaving, dispersing to, and the intensities of removal applied to the stream sections. Crayfish had a greater probability of moving to high density sections with the highest removal treatment. My conclusions suggest that conventional removal efforts (trapping), may fail due to compensatory effects on mortality and dispersal, and that novel approaches such as targeting smaller size classes are required, but only after quantitative predictions and field trials.

The objective of this thesis is the development of a unifying framework for the integration and upscaling of the fluid mechanical, ecological and biomechanical processes occurring in aquatic flows. Particular focus is on the interactions of the fluid motion with aquatic plants and sediments in aquatic systems. Appropriately formulated coupled conservation equations are developed for fluid, sediment, and plant motions. The starting points for their derivation are the continuity and momentum equations written for instantaneous local field variables, for fluid, sediment and aquatic plants. The equations of motion for fluid, sediment and plants (at the stem scale) are averaged over time and space to cope with the temporal and spatial heterogeneity of the flow field near the interfacial boundary and couple the fluid and non-fluid equations of motion. To deal with the possible discontinuity of the time-averaged fields within the averaging time, appropriate definitions and theorems for time-averaging are proposed. Time-averaging is then applied on the equations of motion for each phase to obtain the respective time-averaged equations. Time-averaged equations for the second-order velocity moments are also proposed for mobile-boundary flows. The application of consecutive time-space averaging on the continuum equations led to the development of the double-averaged equations of motion for each phase. Double-averaged continuity and momentum equations have been recently proposed for mobile-boundary flows. In this thesis, the coupled double-averaged continuity and momentum equations are proposed for the sediment material and aquatic plants at the reach scale. Double-averaged equations for the second-order velocity moments have been derived for the case of fluid and sediments. By applying the double-averaging methodology (i) the governing equations are upscaled to the scales relevant to applications, (ii) the fluid motion is rigorously coupled with the non-fluid (plants or sediments) motions, and (iii) the effect of the moving interfacial boundary is introduced explicitly in the governing averaged equations. The derived second-order hydrodynamic double-averaged equations are applied to the analysis of extensive data from Direct Numerical Simulations of turbulent open-channel flows over mobile granular beds (the simulations were performed in the Dresden Technical University by Professor J. Fröhlich's Group). The use of the double-averaged equations provides significant data reduction and assists in the data interpretation. The key physical mechanisms involved in the energy transfers between the fluid mean, form-induced and turbulent fields as well as sediment motions are identified based on the assessment of the terms in the double-averaged balances of kinetic energy.

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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1985. / Vita. Abstract. Includes bibliographical references (leaves 195-205). Also available via the Internet

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