Dissertations / Theses on the topic 'Freshwater invertebrates Effects of water pollution on'

The effect of lake acidification was evaluated, in the field, in terms of its impact on both the structural and functional composition of the macrozoobenthic community. The littoral macrozoobenthic community and water chemistry of 45 Canadian Shield lakes was sampled. The water chemistry variables sampled included pH, total dissolved calcium, conductivity, and dissolved organic acid (measured as colour). Partial canonical correlation analysis and partial regression analysis were used to identify those components of the macrozoobenthic community that most directly reflected pH variability. This was done by first removing from the data that portion of the variability attributable to total dissolved calcium, conductivity, and dissolved organic acids. In addition, the spatial structure in the data was removed by identifying the geographic coordinates of the sampling sites.
In general, the results presented here are not consistent with previous studies where the response of the macrozoobenthic community was related to pH without consideration of confounding covariables. Snails, leeches, mayflies and crayfish have all been cited for their sensitivity to acidification. The present study found these taxa to reflect, not pH variability, but rather attributes of water hardness. Similar results were found for both total zoobenthic biomass and functional feeding group abundance.

Freshwater resources are increasingly subject to pollution because of escalating human population growth, accompanied by urbanisation, industrialisation, and the increased demand for food. Consequently, freshwater quality, and aquatic ecosystem structure and function have been severely impaired. The Swartkops River, which drains an urbanised and industrialised catchment in the Eastern Cape of South Africa, is no exception. An integrated environmental water quality (EWQ) approach is needed to measure the impacts of deteriorating water quality on its aquatic ecosystem structure and function to sustain these vital ecosystem-attributes. In this study, an integrated EWQ approach, which included i) analysis of water physico-chemical variables; ii) macroinvertebrate-based family-level taxonomic- and traits-based community analysis; iii) Chironomidae species-level taxonomic- and traits-based community analysis; iv) Chironomidae deformity-based sub-lethal analysis; and v) experimental investigation of long-term wastewater effluent effects, using model stream ecosystems, were applied to investigate environmental water quality in the Swartkops River. One upstream reference site and three downstream sites in the Swartkops River were monitored over a period of three years (August 2009 – September 2012). The family-level taxonomic community responses based on the South African Scoring System version 5 (SASS5) and a newly developed Swartkops multimetric index indicated very poor river health conditions for the three downstream sites, compared with the good condition of the upstream site. The Chironomidae species-level responses in the three downstream sites provided evidence of differences in biotic impairments, which were not evident with the family-level taxonomic data at these sites, thus highlighting the importance of species identification in freshwater biomonitoring. The family-level traits-based approach (TBA) showed that macroinvertebrates with gills and lungs were more abundant at the upstream site, decreasing markedly at the downstream sites. The relative abundance of macroinvertebrates relying on aerial and tegument respiration increased at the downstream sites compared with the upstream sites. The results of the family-level TBA highlighted the inextricable link between the traits-based approach (TBA) and taxonomic identification, clearly showing that the TBA is additional to, and not an alternative to, taxonomic recognition because important traits, e.g. reproductive cannot be used at a coarse taxonomic identification. A novel chironomid species traits-based functional strategies approach developed in this study, based on species combining similar sets of traits, proved sensitive in diagnosing the main abiotic water physico-chemical stressors. The functional traits responded predictably to deteriorating water quality and provided an adaptive and mechanistic basis for interpreting chironomid species occurrences at the four sampling sites, providing insight into why certain chironomid species occurred at one site but not at the other. Chironomid deformities provided evidence of sub-lethal in-stream biological response to deteriorating water quality. A newly developed deformity-based extended toxic score index proved sensitive, enabling the discrimination of the sampling sites, indicating that a biomonitoring tool based on sub-lethal effects could be used to assess the effects of deteriorating water quality before it reached lethal levels. Empirical evidence based on the taxonomic, traits and sub-lethal responses suggested that the changes in macroinvertebrate community structure were caused chiefly by the discharge of wastewater effluents into the river. This was supported by the model-stream ecosystem results indicating significant effects of effluents on the macroinvertebrate community structure, similar to the observed in-stream responses. The model stream results indicated that improved physico-chemical effluent quality compliance after 50% effluent dilution did not significantly reduce the effects of the effluent on the macroinvertebrate communities, showing that ecologically-based methods rather than physico-chemical measures alone are necessary to assess effluent quality. Finally, the results of the multi-criteria approach were integrated to propose tools to manage environmental water quality in the Swartkops River, and the benefits of the study were highlighted in the context of biomonitoring in South Africa.

Contamination of freshwaters is of concern because of its effect on ecosystem health. The effect of contamination can be assessed at all levels of biological organisation, from the ecosystem level to the molecular level. At the biochemical level, enzymes that are involved in the detoxification of organic chemical contaminants are useful as markers of contaminant exposure as they are often one of the first systems to respond to chemical exposure. Furthermore, changes in the activity of these enzymes may be indicative of effects at higher levels of biological organisation. In this study, the use of the detoxification enzyme glutathione stransferase (E. C. 2.5.1.18) (GST) in the freshwater invertebrate Gammarus pulex (Crustacea: Amphipoda), as a biomarker of organic xenobiotic exposure and effects was assessed. Toxicant induced changes in GST activity were related to changes in energy status and physiological energetics. A GST assay was developed that allowed the rapid analysis of GST activity in up to ninety individual animal samples simultaneously. Optimum sample handling and assay conditions were determined for the assay of GST in G. pulex, and extrinsic factors (e. g. environmental temperature, feeding and holding conditions) and intrinsic factors (e. g. body size), affecting variability of GST activity in G. pulex were assessed The effect of exposure to the organic xenobiotics lindane( an organochlorinein insecticide) and alcohol ethoxylate( a non-ionic surfactand detergent)on GST activity in G.pulex was described. The magnitude and duration of the response of GST activity to exposure to both chemicals was assessed under laboratory conditions and with alcohol ethoxylateu, sing outdoor artificial streams. The use of GST as a marker of pesticide exposure in field populations of G. pulex that were subject to pesticide contamination was studied in comparison with animals from non-contaminated, reference sites. The differences in GST activity between animals from a contaminated site and clean site were investigated by short-term and long-term exposure to lindane in the laboratory. Changes in energy status and physiological energetics were investigated in G. pulex on exposure to lindane by measuring glycogen concentration and scope for growth. Measuring these parameters on short-term and long-term exposure to lindane allowed the sensitivity of these responses to be related to the GST response and allowed the energetic cost of exposure to be assessed. It was concluded that increase in GST activity may providea rapid and sensitive biomarker of xenobiotic exposure in the short-term and in populations subject to pesticide contamination. The affect on GST activity may be indicative of effects at higher levels of biological organisations, such as scope for growth and glycogen concentration However, GST activity is affected by a variety of intrinsic and extrinsic factors and should therefore be used only asp art of a comparative study. Because of the transient nature of the GST response in situ assessments should be based on 24-hour exposure periods.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2005.
Thesis documentation sheet inserted. Appendix reproduces four papers and manuscripts co-authored with R.K. Johnson. Issued also electronically via World Wide Web in PDF format; online version lacks appendix.

The toxic effects of cadmium on aspects of the survival, behaviour and reproduction of Gammarus pulex and Asellus aquaticus are described in some detail. Some of the laboratory procedures were validated in field experiments. The presence of the parasites Pomphorhynchus laevis and Echinorhynchu_s1truttae does not modify the toxicity of cadmium (0.01-1.0 mgl ) to their intermediate-Fost G. pu7ex. Pretreatment for 24 hours with 0-47 μgl cadmium alters the distribution of separation times when precopula pairs of G. pu7ex are disrupted by the invertebrate anaesthetic 2- phenoxyethanol. Precop1la is directly disrupted by exposure to cadmium (0.1-12.7 mgl )_ýut recovery can follow. Pretreatment with cadmium (3-140 μgl ) for 24 hours, of similarly sizeci male G. pulex and subsequent exposure to 0.13 and 2.23 μgl while in competition for access to a female may increase tolerance and enhance reproductive success, or initiate irreversible toxic effects and impair competitive ability. Exposure of female G. pulex-1to 2.0 and 9.6 μg1 , and female A. aquaticus to 40.2 pgl cadmium pre-fertilization reduces their fecundity. Brood development times of G. pulex and A. aquaticus exposed to 2.1 and 12.4 μg1-1 cadmium postfertilization are extended by 2 and 2.7 days respectively. The embryonic development and abortion during brooding are described in detail for A. aquaticus. An explanation of reduced final brood size in Asel7us is Postulated. Growth of juveniles of both test species exposed during brooding is assessed. Single and repeated 24 hour field simulations of acidic deposition demonstrate increased host sensitivity of G. pulex infected with P. 7aevis. The effects of low pH and elevated aluminium concentrations are mitigated to some extent by liming. Six hour field simulations of the individual components of farm waste demonstrated that infected gammarids were more susceptible under conditions of low dissolved oxygen than uninfected conspecifics.

Water hyacinth (Eichhornia crassipes) is a floating non-native plant that has been reoccurring in Lake Chapala, Jalisco, Mexico for more than 100 years. In this research, I explore the effects of water hyacinth on freshwater ecosystems worldwide and specifically on Lake Chapala. In chapter 1, I reviewed studies conducted on water hyacinth worldwide and found that the effects of water hyacinth on water quality are similar but the magnitude of effects is dependent on the percent cover and potentially the spatial configuration of water hyacinth mats. Water hyacinth's effect on aquatic invertebrates, fish, and waterbirds is less predictable and dependent on conditions prior to invasion. In chapter 2, I tested for relationships between percent water hyacinth cover and waterbird abundance, species diversity, community composition, and habitat use. In general, I found a weak positive relationship or no relationship between these variables. In Chapter 3, I monitored habitat use by American Coots (Fulica americana) in a variety of habitats around Lake Chapala. I found that the time spent in water hyacinth positively corresponded to the percent water hyacinth cover and that the time foraging in water hyacinth was positively related to the time spent in water hyacinth. In Chapter 4, I compared invertebrate assemblages in open water to those within and at the edge of water hyacinth mats, emergent vegetation, and submerged trees. I also examined invertebrate assemblages within the roots of water hyacinth plants and compared assemblages between patch and shoreline water hyacinth plants. I found that density and taxonomic richness of water column invertebrates were generally higher in association with water hyacinth, but that mean percent cover of water hyacinth affected the magnitude of differences among habitats and vegetation types. I did not find significant differences in root invertebrate density and taxonomic richness between patch and shoreline water hyacinth plants. In chapter 5, I discuss how water hyacinth affected dissolved oxygen and water transparency on a small, localized scale, but was not the driving factor for seasonal differences. The overall results suggest that water hyacinth had a minimal ecological effect on Lake Chapala during this study.
Ph. D.

Recent evidence strongly suggests that aluminum toxicity is important in determining the structural and functional characteristics of freshwater communities affected by acid precipitation. To determine the effect dissolved aluminum has on lotic invertebrates previously unexposed to anthropogenic acidification, experiments were carried out in a second-order headwater stream 50 km east of Vancouver, British Columbia during August 1982. In three separate experiments, HC1 and/or A1C1₃ were added to Mayfly Creek during daylight hours, increasing acidity from pH 6.9 - 7.0 to pH 5.8 - 6.0 and total aluminum from < 0.1 mg/L to > 1.0 mg/L. Biological response was monitored by sampling invertebrate drift with 86 Mm nets. Relative to an unmanipulated, upstream control site, drift density doubled in response to added H⁺ alone (pH 5.9). When Al₃⁺ was added (pH 5.9) drift density increased fourfold. Following 48 h continuous dosing with HC1 (pH 5.9) there was an even greater response to added Al₃⁺. Ephemeroptera were able to detect dissolved aluminum and responded almost immediately (within 45 min). Similarly, Trichoptera and Chironomidae detected increased H⁺ concentrations and responded immediately. Response to augmented Al₃⁺ by Trichoptera, Hydracarina, and Chironomidae was delayed 6 h. However, pre-exposing animals to 48 h HC1 resulted in enhanced aluminum sensitivity for Chironomidae and for Simulium and Plecoptera, which had not responded within 10 h to H⁺ or Al₃⁺ alone. It is proposed that rapid increases in drift density are due to behavioral escape responses, while delayed responses are probably associated with physiological impairment. Evidence was also obtained suggesting that during early stages of morphological development Ephemeroptera and Chironomidae are more sensitive to increased Al₃⁺ and H⁺ concentrations than during later developmental stages. In laboratory experiments using artificial stream channels, Chironomidae larvae and Ephemeroptera nymphs were exposed to CI⁻ and H⁺ concentrations, equal to those during field experiments. Results showed that drift behavior in these animals is not stimulated by mildly elevated chloride concentrations. These studies demonstrate that increased dissolved aluminum concentrations intensify biological response to acidification, and confirm acid sensitivity patterns for Ephemeroptera and Chironomidae reported by others. The observed acid insensitivity of Plecoptera, simuliids, and Trichoptera also conforms to previously described patterns. Experimentally manipulating this community produced results closely resembling those obtained in similar studies for areas currently affected by acid precipitation. The major difference in results between studies is that invertebrate communities previously unexposed to acidification contain more species sensitive to mild acidification. These latter animals are particularly sensitive to the presence of elevated dissolved aluminum concentrations.
Science, Faculty of
Zoology, Department of
Graduate

Water samples and macroinvertebrates were collected from three stations of Finley Creek, Indiana before and after a surface cleanup of an adjacent hazardous waste disposal site. Water quality parameters: iron, total dissolved solids, conductance, hardness, total suspended solids and pH were compared between stations and years. The water quality above the landfill was high but decreased downstream. The water below the disposal site contained high levels of chemicals in both studies. However, the concentrations of chemicals were lower in the water two years after the cleanup.Numbers of macroinvertebrates and the number of taxa were determined and species diversity indicies were established. The results showed a statistically significant increase in macroinvertebrate taxa and mean species diversity indicies below the waste disposal site after the cleanup. These results indicate an improvement of water quality.
Department of Natural Resources

Thesis (M.S.)--Kutztown University.
Source: Masters Abstracts International, Volume: 45-06, page: 3039. Typescript. Abstract precedes thesis as preliminary leaves [1-4]. Includes bibliographical references (leaves [51-52]).

Microplastics can be defined as “any synthetic solid particle or polymeric matrix, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water”. The growing demand and consequent production of plastic products both at microscale (e.g., personal care products) and at macroscale with inappropriate disposal subsequent degradation in the environment has turned microplastics into global emergent pollutants of the aquatic environment. In fact, the levels of microplastics that have been found in river and lake sediments, raise concern about ingestion and potential negatives effects of microplastics in aquatic benthic invertebrates, particularly those who feed on particulate matter. Possible effects at different levels of biological organisation (sub -organismal up to community level s) are still overlooked , as well as the study of the toxic effects of microplastics to invertebrate biota under relevant exposure scenarios, especially considering climatic change. Therefore, the objective of this thesis was to evaluate the effects of irregularly shaped pol y ethylene microplastics (one of the polymer type microplastics most produced and found in aquatic sediments) using a holistic approach that combines sub -organismal, organismal, population and community level responses, aiming to produce relevant ecotoxicol o gical data for risk assessment of microplastics in freshwaters. First, a quantitative and qualitative assessment of the ingestion of microplastics was evaluated in two model aquatic species, the dipteran Chironomus riparius and the endobenthic oligochaet e Lumbriculus variegatus, as these species feed on particulate matter, being prone to ingest microplastics. Along with the assessment of the ingestion of microplastics, the effects (both at sub -cellular and organismal level) were assessed in an attempt to link ingestion and potential deleterious effects induced by the particles per se. Activation of immune response (phenoloxidase activity), oxidative stress and damage , as well as , effects on life -history traits (larval growth and development) , were observed in C. ripariu s and associated to the augmented ingestion and retention of microplastics in their gut when compared to L. variegatus, which only presented slight evidence of oxidative stress and no effects on reproduction. The combined exposure of microplastics with natural stressors was then performed in Chironomus riparius (the most sensitive species ). Temperature, salinity and food shortage were used as natural stressors relevant under climate change scenarios and that could modulate the ingestion and induced effects of microplastics in relevant exposure scenario s . The results show that interactions between microplastics exposure and these natural stressors are complex and mainly additive and antagonistic effects were observed. However, results also identified conditions (low temperatures and severe food shortage) where sub - lethal effects of MPs to natural populations of C. riparius can be stronger than predicted by standard toxicity assays. These combined exposures revealed that under different environmental conditions, toxicity of MPs is not simply a reflection of internal concentrations of particles. Conceivably the main research gap that subsists is the investigation on the ecological effects of microplastics. For that purpose, this thesis performed a mesocosms approach addressing the effects at the community structure and ecosystem functioning, vital to deliver higher - tier risk assessments . This higher -tier approach (i.e., using artificial streams inoculated with natural benthic invertebrate communities) showed that the exposure to a pool of different -sized polyethylene microplastics affected the macroinvertebrate community structure, mainly by reducing the abundance of deposit -feeders and grazers. The ingestion of microplastics by different invertebrate feeding groups correlated positively with the effects as deposit -feeders and grazers presented the higher number of microplastics inside the organisms’ guts. A slight reduction in primary production was observed and may be a possible direct effect of microplastics on periphyton growth. Only slight effects were observed in terms of leaf litter decomposition signalling that the exposure to polyethylene microplastics might not have affected feeding behaviour of shredders or in turn that exposure period was too short to reveal trait -mediated indirect effects . In conclusion, the present thesis demonstrates that microplastics can be ingested by some aquatic macroinvertebrates and that enhanced ingestion can potentially pose a risk to natural invertebrates’ population. Despite considerable interspecific variation in sensitivity to polyethylene microplastics, their presence in sediments can alter community structure and represent a risk to ecosystem functioning at the long -term. The present thesis confirms that immune responses and oxidative stress as key molecular initiating event s in microplastic toxicity, shows that assessing the internal concentrations of plastic particles is critical for a correct evaluation of effects in biota and highlights the need to incorporate more invertebrate species and relevant exposure conditions for an accurate risk assessment of microplastics in freshwaters.
Os microplásticos podem ser definidos como “qualquer partícula sólida de origem sintética ou matriz polimérica, de forma regular ou irregular e com tamanho entre 1 μm to 5 mm, tanto de origem de produção primária como secundária e que são insolúveis em água”. A crescente procura por este tipo de produtos e consequentemente a sua maior produção, tanto à microescala (p. ex.: produtos de higiene pessoal), como à macroescala com descarte incorreto e consequente degradação no meio ambiente, tornaram os microplásticos num poluente emergente do ambiente aquático à escala global. Assim sendo, os níveis de microplásticos que têm vindo a ser encontrados nos sedimentos de rios e lagos geram preocupação acrescida relativamente à sua potencial ingestão e efeitos gerados por esta em invertebrados bentónicos, particularmente aqueles que se alimentam de matéria orgânica particulada. Existe ainda pouca informação relativamente aos possíveis efeitos provocados pelos microplásticos nos diversos níveis de organização biológica (desde o nível suborganismal até à comunidade), bem como, em relação aos efeitos dos microplásticos em invertebrados sob cenários relevantes de exposição, em especial considerando as alterações climáticas. Assim, o principal objetivo desta tese foi o de avaliar os efeitos de microplásticos com forma irregular de polietileno (um dos polímeros mais produzidos no mundo e também dos mais encontrados nos sedimentos de rios e lagos), usando uma abordagem holística que combina respostas ao nível sub-organismal, organismal, populacional e da comunidade, pretendendo deste modo facultar informação ecotoxicológica relevante que possa ser usada na avaliação de risco dos microplásticos em ambientes dulçaquícolas. Para tal, a ingestão de microplásticos foi avaliada em termos quantitavos e qualitativos em duas espécies bentónicas -modelo, o díptero Chironomus riparius e o oligoqueta Lumbriculus variegatus, que sendo espécies que se alimentam de matéria particulada, estarão mais suscetíveis à ingestão de microplásticos. Paralelamente à avaliação da ingestão de microplásticos, foram também avaliados os efeitos (tanto a nível sub-celular como ao nível do organismo) numa perspetiva de relacionar ingestão e efeitos. Os principais efeitos observados prenderam-se assim com a ativação da resposta imune (medida através da atividade da fenoloxidase), stress e dano oxidativo, bem como efeitos ao nível do ciclo de vida em C. riparius (diminuição do crescimento larvar e atraso no desenvolvimento). Estes efeitos foram assim relacionados com a maior ingestão de microplásticos, quando comparada com a ingestão observada em L. variegatus, que somente apresentou sinais ligeiros de stress oxidativo e ausência de efeitos na reprodução. A espécie mais sensível, Chironomus riparius, foi então exposta a microplásticos em combinação com diversos stressores naturais. Os stressores naturais escolhidos foram a temperatura, salinidade e limitação da disponibilidade de alimento, sendo estes relevantes em cenários de alterações climáticas, e capazes de alterar a ingestão e consequentemente os efeitos provocados pelos microplásticos. Os resultados demonstram que as interações decorrentes da exposição conjunta de microplásticos com os stressores naturais são complexas, sendo que os efeitos observados foram maioritariamente aditivos ou antagonísticos. Contudo, sob determinadas condições como baixa temperatura e significativa limitação da disponibilidade de alimento, os efeitos sub -letais dos microplásticos nas populações naturais de C. riparius poderão ser mais severos que o previsto pelos ensaios ecotoxicológicos padronizados. Estes efeitos combinados revelaram ainda, que sob determinadas condições ambientais, os efeitos tóxicos dos microplásticos poderão não ser simplesmente um reflexo das concentrações de microplásticos encontrada s no interior dos organismos. A avaliação dos efeitos ecológicos da exposição a microplásticos é possivelmente , a principal lacuna que subsiste na investigação. Assim, esta tese procurou colmatar essa lacuna, com recurso a um ensaio usando rios artificiais (mesocosmos), em que foram estudados os efeitos na estrutura da comunidade de invertebrados bentónicos, bem como nas funções providenciadas pelo ecossistema, vitais para uma melhor avaliação de risco. Esta abordagem demonstrou que a exposição a microplásticos de polietileno de diversos tamanhos afetou a estrutura da comunidade, sobretudo através da redução da abundâ ncia de invertebrados coletores de depósito e raspadores. A ingestão de microplásticos pelos diferentes grupos funcionais de invertebrados correlacionou -se positivamente com os efeitos, uma vez que coletores de depósito e raspadores apresentaram o maior número de microplásticos no seu interior . Foi ainda observada uma ligeira redução na produção primária que poderá estar relacionada com um efeito direto dos microplásticos no crescimento do perifíton. De igual modo, observou -se apenas uma ligeira redução na decomposição da folhada, sendo este efeito indicativo de que a exposição a microplásticos de polietileno poderá não afetar significativamente o comportamento alimentar dos fragmentadores, ou em alternativa o tempo de exposição poderá ter sido demasiado curto para que estes efeitos indiretos se possam ter manifestado. Em conclusão, a presente tese demonstra que os microplásticos podem ser ingeridos pelos macroinvertebrados de água doce e representar um risco para as populações naturais. Apesar de se ter verificado uma considerável variação interespecífica na sensibilidade aos microplásticos de polietileno, a sua presença nos sedimentos pode alterar a estrutura das comunidades de macroinvertebrados bentónicos e alterar o funcionamento dos ecossistemas a longo prazo. A presente tese comprova também que a resposta imune e o stress oxidativo são eventos -chave de início a nível molecular na toxicidade dos microplásticos, e demonstra que a avaliação das concentrações internas dos microplásticos é crucial para uma correta avaliação dos efeitos nos organismos. Salienta -se ainda a necessidade da incorporação de mais espécies de invertebrados, assim como, de cenários relevantes de exposição para uma avaliação de risco mais precisa dos microplásticos nos ecossistemas dulçaquícolas.
Programa Doutoral em Biologia e Ecologia das Alterações Globais

Freshwater ecosystems will likely become sinks for future silver loadings as a result of increased nanosilver (n-Ag) use in industrial and commercial applications. A series of bioassays was performed to assess how n-Ag toxicity may be influenced by abiotic factors associated with natural freshwater ecosystems. Additionally, these bioassays provide insight into how environmentally relevant concentrations of n-Ag may sublethaly affect the freshwater benthic gastropod, Physa acuta, that plays pivotal roles in maintaining the structure and function of freshwater ecosystems. In sediment with no benthic organic carbon (BOC), gastropod vital rates decreased in treatments containing any n-Ag, gastropods in sediment with relatively low BOC appeared to trade off growth for reproduction at high n-Ag treatments, while gastropod vital rates in high BOC sediment remained unaffected at all nanosilver treatments. Sediment type may abate nanosilver toxicity as a result of organic carbon content. Effects of n-Ag on gastropod vital rates were not dependant on pH, suggesting aqueous pH does not directly influence n-Ag toxicity. Nanosilver (0.2 μg/L) stressed gastropods, altering their growth and reproduction tradeoff dynamics. Nanosilver concentrations modeled to exist in natural freshwaters, disrupted gastropod ability to detect and respond to a natural predator, while greater n-Ag concentrations stimulated gastropods to exhibit contaminant avoidance behavior and thereby attempted to flee their habitat. This study provides direction in understanding how adverse n-Ag effects may be influenced by abiotic parameters, while assessing sublethal effects of n-Ag on freshwater gastropods that are likely to occur in natural freshwater ecosystems, given current estimates of environmental n-Ag concentrations.
Department of Biology

Ph.D.
Except for agriculture, the mining industry is considered as not only the oldest but also the most important industry. Mining involves the removal of minerals from the earth's crust for usage by mankind. The disturbance during mining activities such as mining effluent has an effect on the natural aquatic environment. In any freshwater environment, the macroinvertebrates form a vital link between the abiotic envinronment and the organisms in higher trophic levels. It is thus true that specific environmental contaminants, such as mining effluent, may directly affect the survival of macorinvertebrates. The density and diversity of macroinvertebrates is in a direct relation with the water quality. For the purpose of this study, attention was given to the effects of gold and coal mine effluent on the macroinvertebrate fauna, as well as to the determination of metal accumulation from the water through the macroinvertabrates to fish. At Case Study Mine One, with an open water system, acidic conditions of the water caused a reduction in the number and diversity of macroinvertebrates. A closed water system, characteristic of Case Study Mine Two, presented a slightly more abudandant macroinvertebrate population than with the previous mine. The results lead one to conclude that the surface water in this study area is of a better quality. Case Study Mine Three had a complex water circuit and presented a greater number and diversity of macroinvertebrates, with the best water quality of the three mines investigated.

M.Sc. (Zoology)
The Limpopo Province covers an area of 12.46 million hectares and these accounts for 10.2 per cent of the total land area of the Republic of South Africa. The province is endowed with abundant agricultural resources and it is one of the country’s prime agricultural regions noted for the production of fruits and vegetables, cereals, tea, and sugar. A key feature of the agricultural industry of Limpopo Province is its dualism. There are two distinct types of agricultural production systems. The large scale commercial farming system occupies approximately 70% of the total land area. The smallholder farms are located mostly in the former homeland areas and they cover approximately 30% of the provincial land surface area. The town of Thohoyandou, with its surrounding villages, is the area of greatest human concentration in the Luvuvhu Catchment and subsistence farming is about a third of the total agricultural component. It is important to study the effects of agricultural inputs (e.g. fertilizers and sediment loads) on aquatic ecosystems in order to fully understand the processes involved of these stresses on aquatic ecosystems. Knowledge of these impacts toward the environment and human health is often limited due to lack of capacity building, especially among small scale farmers. Ten bio-monitoring sites were studied on five systems in the Vhembe district. The sites were sampled during the low flow period of November 2011 and the high flow period of April 2012. Sampling sites were selected to present conditions in the Mutale, Mutshindudi and Tshinane Rivers upstream and downstream of the potential influence of small scale agricultural activities...

Content removed due to copy right restriction: Dewson, Z.S., Death, R.G. & James, A.B.W. (2003) The effects of water abstractions on invertebrate communities in four small North Island streams. New Zealand natural Sciences 28, 51-65.
Small streams are often used for small-scale water abstractions, but the effects of these water abstractions on the instream environment, invertebrate communities and ecosystem functioning of small permanent streams is poorly understood. This research extends current knowledge by surveying existing water abstractions and completing flow manipulation experiments in the field. Reduced discharge often decreases water velocity, water depth, and wetted channel width and can increase sedimentation, modify the thermal regime and alter water chemistry. In a survey of sites upstream and downstream of existing water abstractions, I found that downstream sites had higher densities of invertebrates, but fewer taxa sensitive to low water quality compared with upstream sites. There were greater differences in physicochemical characteristics such as velocity and conductivity and in invertebrate communities between upstream and downstream sites on streams where a larger proportion of total discharge was abstracted. Using before-after, control-impact (BACI) designed experiments, weirs and diversions were created to experimentally decrease discharge by over 85% in each ot three small streams, ranging from pristine to low water quality. The response of invertebrates to short-term (one-month) discharge reduction was to accumulate in the decreased available area, increasing local invertebrate density. After a year of reduced flow, the density of invertebrates and percentage of mayflies, stoneflies and caddisflies decreased at the pristine site, whereas only taxonomic richness decreased at the mildly polluted stream. Reduced discharge had no affect on the invertebrate community at the stream with the lowest water quality. Reduced discharge had little influence on leaf decomposition rates, but distances travelled by released coarse particulate organic matter (CPOM) increased with increasing discharge. The effects of reduced discharge on primary production were not consistent between streams. Overall, the severity (magnitude/duration) of flow reduction appeared to influence invertebrate responses to water abstraction although the outcomes of water abstraction were dependent on the invertebrate assemblage present in each stream.