South Africa has a long history of problems with invasive alien species. In an assessment of alien invading plants and water resources in South Africa Versveld et al. (1998) estimated that Invasive Alien Plants (IAPs) in South Africa covered an area equivalent to the size of KwaZulu-Natal. However this area of invasion was primarily concentrated along the river courses of South Africa as alien invasions are arguably a riparian problem (Versveld et al., 1998). In a 1998 assessment of the distribution of IAPs in South Africa Versveld et al. (1998) found a total invasion extent of 8% for South Africa (including Lesotho), while KwaZulu-Natal had a higher total extent of invasion at 9.75%. However the authors noted the limitations of the IAP mapping assessment and stated that from personal observations and observers’ comments the area invaded by IAPs may be as much as 2-3 times greater than the 9.75% value obtained for KwaZulu-Natal. South Africa’s most widespread invasive alien tree (Dye and Jarmain, 2004), Acacia mearnsii (black wattle), is ubiquitous throughout KwaZulu-Natal, and invades most severely where water is plentiful, such as along watercourses and road verges. However following dispersal along rivers, A. mearnsii spreads into adjacent terrestrial habitats (Richardson and Kluge, 2008) including indigenous grassland and forest. A. mearnsii was introduced to South Africa in the middle 19th century to provide tanbark, woodchips, construction poles and firewood, and its introduction spread rapidly across KwaZulu-Natal through farmers and foresters (Henderson, 2001; WESSA, 2008). River and riparian zone rehabilitation is becoming accepted as having an essential role to play in the long term solution of water resource quality and supply problems and environmental health as a whole. As a result the impact of IAP invasions on water resources, ecological habitats and the delivery of ecosystem goods and services has undergone much scientific investigation (van Wilgen et al., 2008). Numerous studies have shown that, under most circumstances, removal of IAPs results in a general increase in streamflow and returns a stream to a more natural seasonal flow regime. However, scientific studies on the influences of woody IAPs on the hydrogeomorphology of riparian areas, and the resultant effects on stream hydrology and ecology, have undergone little scientific investigation in the South African context. Hydrogeomorphology studies the linkages of surface and subsurface water, and hydrological processes with landforms and geomorphic processes in temporal and spatial dimensions. As a result the discipline is well applied to the study of the interaction of, and interdisciplinary impacts of IAPs on riparian areas. Macdonald (2004:22) stated that there is a need to “investigate the interaction of IAPs with other aspects of water quality, for example soil erosion rates, including river channel and bank erosion.” In the early 1990s, after a study assessing the potential impact of IAPs on the geomorphology of river channels in South Africa, Rowntree (1991) stressed that further research on the influence of IAPs on stream geomorphology is required to guide truly effective riparian zone management. Since this study, little scientific work has been undertaken on this topic in the South African context. The literature review portion of this dissertation reviews the findings of various researchers as to how IAPs physically influence riparian habitats, specifically with reference to the role of IAPs in degrading riparian and streambank landscapes to an extent that streambank stability and stream channel form is adversely affected. This topic is introduced by illustrating the many functions that riparian zones can perform and some of the possible consequences of a loss of riparian habitat integrity. Worldwide awareness of the functions and values of riparian systems has led many countries to perform inventories of threatened and valuable riparian areas. A database of stream habitat integrity is useful for environmental impact assessments, development planning and resource inventories. Thus a multitude of stream survey and aquatic health sampling techniques and methodologies have been developed, some of which could be applied to assessing the influence of IAPs on riparian zones. 1.1 Research Aims and Objectives This dissertation forms a research study based on field research centred around field methods and tools developed after a review of relevant literature. The key aims of this research study are to; · refine an international river habitat survey method for application within South Africa, and · develop a test case to implement the developed method in analysing the impacts of IAPs on stream hydrogeomorphology in small headwater streams of KwaZulu-Natal, South Africa. These aims are achieved through the following objectives; · investigate the current body of knowledge covering the impact of woody IAP invasions on streambank stability and channel form, · review available stream survey methods and develop a stream survey methodology which can be applied to investigate the relationships between woody IAP invasions and streambank stability and form within headwater streams of KwaZulu-Natal, · investigate the relationships illustrated by the data after applying the developed stream survey tools and fieldwork methodology, and · discuss any shortfalls of the developed tools and methods, and suggest future needs. The hypothesis of the study contends that, within the focus of this study, invasion of headwater streams by woody IAPs can result in; · increased channel incision and bank steepening, and · an increase in streambank instability. 1.2 Document Structure Chapters 2 to 4 form a review of current literature to establish a base of understanding of the implications, processes and components involved in the invasion of riparian zones by Invasive Alien Plants. In Chapter 5 the approaches to stream surveying are assessed and selected methods of stream survey seen as applicable to this study are reviewed. Based on these findings, a method of stream survey for application in this study is developed and described in Chapter 6 following a description of the fieldwork sites and methodology. Chapter 7 provides an extensive analysis and exploration of the results of the various components of the fieldwork, which are then discussed in Chapter 8. Chapter 9 outlines final conclusions, analysis of the applicability of the findings, and suggestions with regards to future research needs. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

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No. of bitstreams: 2 Tese - Denis Silva Nogueira - 2015.pdf: 6759912 bytes, checksum: d94527b0911d75bd269ddbf67184a1ce (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-03-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Lotic ecosystems are highly complex interacting with acting factors in different spatial and temporal scales. Small forested streams receive direct influence of the surrounding vegetation through the input of organic matter which is the base of the food chain in these ecosystems. I studied the effect of the reduced-impact selective logging on communities of aquatic insects streams to test the hypothesis that communities are affected by their impacts. Despite the metrics used appropriately capture the impact, there were no negative effects on insect communities. However, the results of this study may not be generalizable to other systems because we studied only a fraction of the diversity of Amazonian streams, specifically the insect orders Trichoptera, Plecoptera and Coleoptera. In addition, the absence of the low impact management effects is dependent on the operating system adopted in each enterprise. Another predominant feature in any lotic ecosystem is its directional flow, which consequently affects the distribution of substrates, habitats, and food resources within the streams. I studied the effects of water flow taking it as the main predictor of the selective effect of habitat on the attributes of insect taxa. My hypothesis was confirmed by showing that most rapid flowing streams in Amazon has faunas with morphological and ecological attributes of greater resistance to flow. Environmental factors such as the preference for habitats, dispersive limitation and biotic interactions are among the main mechanisms responsible for structuring communities, and has been widely emphasized in the context of metacommunity theory. A metacommunity is defined as the set of communities in a region which are interconnected by the flow of individuals, which emphasizes the spatial dynamics in structuring the diversity and composition of species in each local community. I tested the effects of environmental factors, spatial filters and biotic interactions in aquatic insects of forested streams of the Amazon, specifically the intraguild segregation and interguild predation effect. My results support the existence of predation effects on the organization of the metacommunity, as evidenced by the exclusive fraction of the predators matrix on prey assemblages of different guilds, and still withstand environmental effects and dispersive limitation in different trophic guilds. The study developed in this thesis help us understand more clearly the effects of the selective logging impacts on aquatic insect communities, assist in understanding about what are the characteristics of the stream habitats filter ecological and morphological attributes of aquatic insects in the Amazon, and advance our understanding of the effects that biotic interactions may have on the structuring streams metacommunities. / Ecossistemas aquáticos lóticos são altamente complexos interagindo com fatores atuando em diferentes escalas espaciais e temporais. Especialmente pequenos riachos florestados recebem a influência direta da vegetação circundante por meio da entrada de matéria orgânica a qual representa a base da cadeia alimentar nestes ecossistemas. Estudei os efeitos do corte manejado de madeira sobre as comunidades de insetos aquáticos de riachos, testando a hipótese de que as comunidades seriam afetadas por estes impactos. Apesar das métricas utilizadas capturarem apropriadamente os impactos, não houveram efeitos negativos sobre nenhum aspecto das comunidades estudadas. Entretanto, os resultados deste estudo não podem ser generalizados considerando que estudamos apenas uma parcela da diversidade dos riachos, especificamente as ordens Trichoptera, Plecoptera e Coleoptera. Além disso, a ausência de efeitos do manejo de baixo impacto é dependente do regime de exploração adotado em cada empreendimento. Outra característica predominante em qualquer ecossistema lótico é seu fluxo direcional da correnteza, que por conseguinte, afeta a distribuição dos substratos, habitats, e de recursos alimentares dentro dos riachos. Estudei os efeitos da velocidade do fluxo tomando-o como o principal preditor do efeito seletivo dos hábitats sobre os atributos das espécies. Minha hipótese foi corroborada, mostrando que riachos de águas mais correntes apresentam faunas com atributos morfológicos e ecológicos de maior resistência a correnteza. Fatores ambientais, como a preferência por habitats, limitação dispersiva e interações bióticas estão entre os principais mecanismos responsáveis pela estruturação de comunidades, e tem sido amplamente enfatizados no contexto da teoria de metacomunidades. Uma metacomunidade é definida como o conjunto de comunidades numa região que são interligadas pelo fluxo de indivíduos, o que enfatiza a importância das dinâmicas espacias estruturando a diversidade e composição de espécies em cada comunidade local e para a diversidade regional. Testei os efeitos de fatores ambientais, filtros espaciais e interações bióticas em insetos aquáticos de riachos florestados da Amazônia, especificamente padrões de segregação intraguildas, como um sinal de competição, e da predação entre guildas, assumindo explicitamente que a abundância e distribuição de predadores devem seguir a disponibilidade das presas consumidas. Meus resultados suportam a existência de efeitos de predação sobre a organização da metacomunidade, como evidenciado pela fração exclusiva da matriz de predadores sobre a comunidade de presas de diferentes guildas, além de suportar efeitos ambientais e limitação dispersiva em diferentes guildas tróficas. Os estudo desenvolvidos na presente tese ajudam a compreender mais claramente como os efeitos dos impactos do corte seletivo de madeira podem afetar comunidades de insetos aquáticos, auxiliam na compreensão de quais são as características dos hábitats selecionando atributos ecológicos e morfológicos de insetos aquáticos na Amazônia, e avançam nossa compreensão dos efeitos que as interações bióticas podem causar sobre a estruturação das metacomunidades de riachos.

M.Sc. (Zoology) / Sediment contamination occurs as a result of various anthropogenic activities; mainly through mining-, agricultural- and industrial practices. Many of the contaminants arising from these activities enter the aquatic system and precipitate from the surrounding water, binding to sediment particles. In the sediment compartment, these contaminants reach concentrations much higher than in solution with the overlying water. Even though the quality of the overlying water may prove acceptable in accordance to water quality uidelines, an aquatic system may still be at risk from the contaminated sediment. If the contaminated sediment were to be disturbed through flooding, bioturbation or changes in the water chemistry, these contaminants will desorb into the water column and as a result be detrimental to life forms in contact and dependent on that water source. Monitoring sediment has been a widespread initiative internationally and has led to the development of various sediment toxicity test methods, including different bioassays. This study focused on sediment bioassays such as the Phytotoxkit-F and Ostracodtoxkit-F, and the Diptera bioassay to assess the sediment quality of the Tweelopiespruit-Rietspruit-Bloubankspruit (TRB) river system in Gauteng, South Africa. This river is known to be impacted by acid mine drainage (AMD) since late August 2002. Exposure of the bioassays to river sediment from preselected sampling sites (Site 1, closest to the mine, to Site 6, furthest from the mine, and Site 7, the reference site) provided an eco-toxicological estimation of the acute toxicity emanating from contaminants in the sediment. Physico-chemical analyses revealed high concentrations of metals and other contaminants in the water and sediment. A general linear decrease in contaminant concentrations was observed from Site 1 to Site 6. The results from the bioassays displayed a similar trend, since there were greater sensitivities (mortalities and growth inhibition) to sediments sampled closer to the mine. Due to high levels of contamination in sediments, compared to the overlying water, and the potential impact on aquatic organisms, sediment toxicity monitoring should be a compulsory requirement for environmental studies in South Africa

M.Sc. Aquatic Health) / The Klip River runs past heavy urbanization and industrialization as a consequence it is possibly one of the most abused river systems in Gauteng and perhaps the country as a whole. Eight sites were selected along the course of the Klip River for biomonitoring purposes. The sites were selected to represent the upper, middle and lower reaches of the river, while sites representing point source pollution sources were also included. Various biomonitoring techniques have been included to determine the present ecological state of the Klip River. This includes biotic indices to assess the ecological integrity of the fish and invertebrate communities and the habitat. In addition, fish health was assessed using a variety of histological, biomarker and bioaccumulation based assessments. From the results it is evident that the sites on the Klip River represent the three main regions of a river including headwaters, middle reaches and a mature river. These natural changes in river ecology also caused natural variations in the habitat availability and the resultant biotic communities. There were, however, many changes not related to these natural variations but rather the numerous anthropogenic activities present on the river. The most noticeable change has occurred due to alteration in the flow regime. These changes are brought about by the many weirs and bridges in the system, return flow from the numerous settlements and agricultural activities and the various WWTW. These alterations in flow have caused serious erosion of the stream banks and may lead to siltation of the system. It is clear from the results of the sediment particle size analysis that there is an increase in the percentage contribution of medium and very fine sand below site 3. This is a good indication that the increased flow below the Olifantsvlei WWTW is already causing siltation. Ultimately this can lead to loss of riffle habitat within the river. These flow alterations have also caused an alteration to habitat availability and quality and as a result caused a modified invertebrate community. The macroinvertebrate community at all the sites (below site 1) consisted of taxa that are tolerant to pollution. This is also reflected in the poor SASS 5 and ASPT scores observed at the various sites. These tolerant organisms probably occur in the system due to an altered habitat template and a change in water quality. It is important to note that although the values obtained for the water quality variables are within the TWQR that the oxygen saturation at some sites decreased. These sites included the sites below the Olifantsvlei WWTW, after the confluence with the Rietspruit and the last monitoring site. The Fish Health Assessment Index scores were the highest at site 3 and decreased to site 8. This indicated that the fish condition improved from site 3 to site 8. However, there was a large variation in the index scores from the individual specimens. The results of this assessment cannot be compared to other studies as no fish health assessment index has been applied on the Klip River. This study will serve as a baseline assessment for future studies of the fish health of the Klip River. The results of the metal analysis in the fish muscle tissue indicated relatively low levels that correspond to levels measured by Kotze (1999) while still being lower than fish sampled from the polluted Olifants River. It is therefore recommended that further studies be completed on the fish health of the Klip River and that the fish health of specimens in the Klip River is compared to those of the Vaal River to determine the impact of the Klip River system on the Vaal River. As it has become clear that the Rietspruit also influences the water quality of the Klip River it is recommended that further studies be completed on the Rietspruit to determine the cause of the impacts. Because the histological alterations identified may be the result of a range of different biological and/or chemical stressors, it is difficult to assign specific causative agents for the various alterations identified. Based on the selected parameters investigated, the results show that fish in the Klip River appears to be in a relatively healthy condition and the organs seem to be in a functional state. Establishing a histology-based monitoring programme for fish health in the Klip River, by incorporating appropriate sample sizes and various fish species is recommended. Monitoring of biological responses for assessing the significance of pollutants has become a reasonable measurement in biomonitoring, and use of biomarker responses has played a significant role in this aspect. However, no biomarker has been validated as a unique tool to determine the effects of pollutants on organisms. Furthermore, it is necessary to understand how bioaccumulation and biomarkers relate to each other on exposure to specific pollutants and how it varies between species, to interpret the effects of pollutant exposure in both the field and laboratory. The results obtained in this study indicate that there are definite impacts on the entire system, although these have not altered fish biology and functionality to a large extent. However, sample size should be considered when evaluating individual biomarker responses, as a larger sample size will be more representative of the resident fish community’s response to the pollutants and other stressors. It is difficult to assign specific stressors for the various biomarker responses identified. It is recommended that further biomarker studies be undertaken on the Klip River to increase the level of confidence in the results obtained.

M.Sc. / The purpose of this study was to determine whether unpaved roads in commercial forests have a detrimental impact on aquatic macro-invertebrates in the receiving rivers associated with these roads. The upper section of the headwaters of the Motlhaka-Semeetse River was chosen as the Study Area because a portion is situated in the Wolkberg Wilderness area (natural area with no roads) and a portion in a commercial forestry plantation (high road network density). Stream conditions based on a rapid bio-assessment of aquatic macro-invertebrates using SASS5 were then compared between the two catchments amid 2002 and 2010. In order to support the SASS5 results, daily rainfall data from December 1959 to October 2010 was collated and compared to daily stream flow data from January 1960 to October 2010. In addition, geomorphological and instream habitat changes in the river between the two catchment areas were recorded, as well as the condition of stream crossings and their linkage to stream networks in the afforested catchment. The SASS5 results revealed that stream conditions at the upper unimpaired site were significantly better, visibly and statistically (p < 0.05) than conditions at the lower site within the forestry plantation. In addition, there were noteworthy changes in the catchment hydrology, the geomorphology and instream habitat between the natural and afforested catchments. Road network densities in commercial forests are mostly considerably higher than suggested in literature and exceed stream network densities. Roads increase the surface area for interception of rainfall and the runoff from this high density of roads results in modification of the catchment hydrology, geomorphology and instream habitat of receiving streams. This physical change to the receiving streams is one of the main reasons for the deterioration in SASS5 results, disproving the hypothesis that road networks in forestry areas have no impact on receiving aquatic ecosystems. Commercial forestry in South Africa needs to improve their road planning, layout, management and maintenance to reduce these environmental impacts. In doing so, the road network density will be reduced with considerable environmental and economic benefits.

MEnv.Sc / Department of Geography and Geo-Information Sciences

Biomanipulation im Sinne einer top-down Steuerung des Nahrungsnetzes wurde in Standgewässern intensiv erforscht und wird als Mittel zur Verbesserung der Wasserqualität bzw. Verringerung der Eutrophierungserscheinungen eingesetzt. Ebenso könnte die Idee der Biomanipulation genutzt werden, um die Eutrophierung in kleinen Fließgewässern zu verringern. Eine Förderung benthischer herbivorer Schlüsselorganismen (z.B. Eintagsfliegenlarven) durch die Reduzierung des Fischfraßdruckes könnte helfen, Algenmassenentwicklungen zu vermeiden. Studien zur Biomanipulation von Nahrungsnetzen in Standgewässern zeigten allerdings eine zunehmende Entwicklung von planktischen invertebraten Räubern bei Abwesenheit planktivorer Fische. Die Bedeutung des Fraßdruckes invertebrater Räuber in fischfreien Fließgewässernahrungsnetzen ist dagegen noch unbekannt. Aufgrund von letalen und subletalen Fischeffekten könnte die Konsumtion räuberischer Invertebraten bei Fischabwesenheit so stark gefördert werden, dass das Ziel der Biomanipulation verfehlt wird. Invertebrate Räuber haben insgesamt einen relativ hohen Anteil an der Biomasse der Benthosgemeinschaft in Fließgewässernahrungsnetzen. Sie könnten somit potentiell einen ähnlichen Fraßdruck wie vertebrate Räuber (z.B. benthivore Fische) auf die unteren trophischen Ebenen ausüben. Auch der Anteil der Omnivorie ist in Fließgewässernahrungsnetzen hoch. Ziel dieser Arbeit war es deshalb, die Bedeutung invertebrater Prädation im Nahrungsnetz eines kleinen Fließgewässers (Gauernitzbach) unter Berücksichtigung der obligaten Räuber sowie des räuberischen Potentials Omnivorer abzuschätzen. Außerdem wurde der Einfluss benthivorer Fische auf die Populationsentwicklung und das Ernährungsverhalten der wichtigsten invertebraten Räuber und Omnivoren untersucht. Dazu wurde ein Bachabschnitt, der mit benthivoren Fischen (Gobio gobio, Barbatula barbatula) besetzt war, mit einem fischfreien Abschnitt über zwei Jahre verglichen. Nach der Identifizierung wichtiger Räuber- und Omnivorenarten anhand ihrer Biomasse und ihrer trophischen Positionen mittels Isotopenanalyse wurde ihr Gesamtfraßdruck abgeschätzt. Invertebrate Prädatoren im Nahrungsnetz des Gauernitzbaches waren Rhyacophila fasciata und Plectrocnemia conspersa (Trichoptera), Isoperla grammatica (Plecoptera) sowie Dugesia gonocephala (Turbellaria). Wichtige Omnivore aufgrund ihrer hohen Biomassen waren Gammarus pulex (Amphipoda) und Hydropsyche spp. (Trichoptera). Anhand eines Mischungsmodells (ISOSOURCE), das auf der Basis der stabilen Isotopensignaturen d13C und d15N die einzelnen Ressourcenanteile einer gemischten Signatur berechnet, konnte das ausgeprägte räuberische Potential der Omnivoren gezeigt werden, da sie einen hohen tierischen Anteil in der Nahrung aufwiesen (20-90 %). Im Nahrungsnetz des Gauernitzbaches waren Omnivore als Räuber damit ebenso bedeutsam wie obligat räuberische Invertebrate. Der Gesamtfraßdruck der invertebraten Räuber und Omnivoren auf die Beuteorganismen (bis 16 g TM m-2 a-1) in der Fischstrecke war höher als der Fraßdruck der benthivoren Fische (~3 g TM m-2 a-1). Dieser Unterschied lag hauptsächlich in höheren täglichen Konsumtionsraten bei ähnlich hohen Biomassen der Invertebraten begründet. Durch die Analyse der stabilen Isotope von Kohlenstoff und Stickstoff konnten die trophischen Beziehungen im Nahrungsnetz des Gauernitzbaches identifiziert werden. Dabei stellten allochthone Kohlenstoffquellen im Frühjahr und Herbst die bedeutendste Ressource für die Primärkonsumenten dar, während autochthone Ressourcen nur im Frühjahr für wenige Herbivore relevant waren. Dies spiegelte sich ebenso in der Nahrung der Omnivoren wider, die neben Organismen hauptsächlich Detritus nutzten. Ebenso zeigten die invertebraten Räuber eine deutliche Abhängigkeit vom allochthonen Kohlenstoff über die Nutzung der Primärkonsumenten. Letale Effekte der Fische auf die räuberischen und omnivoren Populationen im Gauernitzbach fanden hauptsächlich in Abhängigkeit von den bewohnten Habitaten statt. Die Pool-Arten (P. conspersa, D. gonocephala, G. pulex) entwickelten geringere Biomassen in der Fischstrecke, während die Biomassen riffle-bewohnender Invertebraten (R. fasciata, I. grammatica, Hydropsyche spp.) nicht deutlich reduziert wurden. Dabei waren allerdings meist hohe Biomassen in der Fischstrecke weniger stark ausgeprägt als in der fischfreien Strecke. Die Adulten der untersuchten Arten wurden oft stärker letal beeinflusst als die Juvenilstadien. So war die Emergenzproduktion der räuberischen Köcherfliegen und die Abundanz großer und eiertragender Weibchen von G. pulex in der Fischstrecke deutlich verringert. Subletale Effekte der Fische traten im Gauernitzbach in Abhängigkeit von den Ernährungstypen auf. Während die adulten räuberischen Köcherfliegenarten R. fasciata und P. conspersa keine negative Beeinflussung der Fitness und Größe zeigten, emergierte die omnivore Köcherfliege H. instabilis in der Fischstrecke kleiner als in der fischfreien. Außerdem unterschieden sich die Antworten der omnivoren Arten vermutlich aufgrund ihrer unterschiedlichen Lebenszyklen. G. pulex zeigte als ausschließlich aquatisch lebende Art keine subletalen Kosten (unveränderte Fitness) bei Fischanwesenheit wie dies für die omnivore merolimnische Insektenart H. instabilis beobachtet wurde. Die mittlere Fitness der Populationen (gemessen an der Eiproduktion pro Zeit- und Flächeneinheit) war für alle untersuchten invertebraten Räuber und Omnivoren bei Fischanwesenheit deutlich geringer als in der fischfreien Strecke. Für die Räuber (R. fasciata, P. conspersa) und G. pulex waren vermutlich letale Fischeffekte für den geringen Reproduktionserfolg verantwortlich. Dagegen wurde die Fitness der Population von H. instabilis durch die Kombination aus der geringeren individuellen Körpergröße (subletal) und den schwachen letalen Effekten auf die Emergenz reduziert. Der Einfluss der Fische auf die räuberischen Larven von R. fasciata und P. conspersa resultierte in einem Wechsel der Beutezusammensetzung, nicht in der Reduzierung der täglichen Fraßaktivität. Dies war vermutlich auf eine Aktivitätsänderung des Räubers R. fasciata bzw. auf die veränderte Beuteverfügbarkeit für P. conspersa unter Fischeinfluss zurückzuführen. Eine grundsätzliche Verringerung der Fraßaktivität oder der tierischen Anteile in der Nahrung der omnivoren Arten unter dem Einfluss benthivorer Fische wurde nicht festgestellt. Dagegen änderten sich die Relationen der Ressourcen Omnivorer zueinander, so konnte in der fischfreien Strecke eine flexiblere Ressourcennutzung nachgewiesen werden. Die jährliche Gesamtkonsumtion der räuberischen und omnivoren Invertebraten wurde durch die Anwesenheit der benthivoren Fische um 20-50 % reduziert, wofür hauptsächlich fischinduzierte Biomasseänderungen verantwortlich waren. In der fischfreien Strecke konnte dagegen die erhöhte Konsumtion der Invertebraten den fehlenden Fischfraßdruck mehr als kompensieren. Allerdings änderte sich die beutespezifische Konsumtion der Räuber in der fischfreien Strecke durch den verhaltensinduzierten Wechsel in der Beutezusammensetzung. Damit fand ein erhöhter Fraßdruck auf detritusfressende Arten (z.B. Diptera) statt, während die vermuteten Schlüsselarten einer potentiellen Biomanipulation (grazende Eintagsfliegen) in der fischfreien Strecke relativ unbeeinflusst blieben. Da die invertebrate Prädation in Fließgewässern sehr bedeutend sein kann, ist Biomanipulation nur unter Berücksichtigung aller Populationen räuberischer Invertebraten möglich. Nur durch Einstellung einer optimalen (relativ hohen) Biomasse geeigneter benthivorer Fischarten kann eine ausreichende Hemmung der invertebraten Räuber erreicht werden, so dass grazende Arten indirekt profitieren. / Biomanipulation (top-down control of the food webs) in lakes was intensively studied and can today be regarded as an important tool for improvement of the water quality and eutrophication. Similarly, the idea of biomanipulation can be used to reduce eutrophication phenomena in streams. The enhancement of benthic herbivorous key species (e.g. mayflies) by reduction of fish predation pressure could prevent exploding benthic algae biomass. Studies dealing with trophic cascades in lakes suggested that biomass of planktic invertebrate predators is increasing in the absence of planktivorous fish. But until now the importance of invertebrate predation pressure in fishless stream food webs is hardly known. Due to lethal and sublethal fish effects the consumption of predatory invertebrates could be enhanced by the absence of fish to such an extent that biomanipulation could be off target. In general, the proportion of invertebrate predators to the biomass of the benthic community in stream food webs is relatively high. Therefore, invertebrate predation on benthic prey can be as important as vertebrate predation (e.g. by benthivorous fish). Furthermore, omnivory occurs frequently in streams. Therefore, the aim of this thesis was to assess the importance of invertebrate predation in a food web of a small stream (Gauernitzbach) including the obligatory predators as well as the predatory potential of omnivores. Furthermore, the impact of benthivorous fish on population dynamics and feeding behaviour of the most important predators and omnivores was studied. Therefore, a reach stocked with benthivorous fish (Gobio gobio, Barbatula barbatula) was compared with an upstream fishless reach over a two-year period. After identification of important predators and omnivores based on their biomass and trophic position by stable isotope analyses their total consumption was estimated. Rhyacophila fasciata and Plectrocnemia conspersa (Trichoptera), Isoperla grammatica (Plecoptera) as well as Dugesia gonocephala (Turbellaria) were the invertebrate predators in the food web of Gauernitzbach. Because of their high biomasses the most important omnivores were Gammarus pulex (Amphipoda) and Hydropsyche spp. (Trichoptera). Using a mixing model (ISOSOURCE) that estimates the proportions of single resources on a mixed signature on the basis of the stable 13C and 15N isotopes, the predatory potential of both omnivores was pronounced by a high animal food proportion (20-90%). In this stream food web the predation impact of omnivores was comparable to this of obligatory predacous invertebrates. The total invertebrate predation pressure (up to 16 g TM m-2 a-1) in the fish reach was higher than the vertebrate predation pressure (~3 g TM m-2 a-1) mainly caused by the higher daily consumption rates and similar biomass compared to fish. Using stable isotope analyses of carbon and nitrogen the trophic pathways in the food web of Gauernitzbach could be identified. The most important resources for primary consumers in spring and autumn were allochthonous carbon sources. Autochtnonous carbon sources were only utilized by a few herbivores in spring. This was also reflected in the food of omnivores which assimilated mainly detritus beside animal material. Similarly, the predators depended distinctly on the allochthonous pathway by feeding primary consumers. Lethal fish effects on the predatory and omnivorous invertebrate populations were mainly depended on their preferred habitats. Pool-dwelling species (P. conspersa, D. gonocephala, G. pulex) showed decreased biomass in the presence of fish. Contrary, the biomass of riffle-dwelling invertebrates (R. fasciata, I. grammatica, Hydropsyche spp.) was not significantly reduced in the fish reach. Thereby, the highest biomass values in the fish reach could not reach the same level as in the fishless reach. Adults of the investigated species were influenced more lethal than the young stages. Hence, the emergence production of the predatory caddisflies and the abundance of the biggest and gravid females of G. pulex were reduced in the fish reach. Sublethal fish effects existed in dependence on the feeding groups of the invertebrates in Gauernitzbach. Whereas the adult predatory caddisflies R. fasciata and P. conspersa did not show disadvantages in fitness and size, the omnivorous caddisfly H. instabilis emerged with smaller size in the fish reach than in the fishless reach. Different responses of both omnivorous species were observed because of their different life cycles. The exclusively aquatic living G. pulex was not influenced sublethal by fish as the merolimnic insect species H. instabilis. The average fitness of population (measured as egg production per unit time and space) of the studied invertebrate predators and omnivores was distinctly reduced in the fish reach compared to the fishless reach. Probably, lethal fish effects were mainly responsible for the low reproductive success of the predatory species (R. fasciata, P. conspersa) and G. pulex. In contrast, the reduction of population fitness of H. instabilis was caused by the reduced individual adult size (sublethal effect) in combination with the weak lethal effect on emergence. The impact of fish on the feeding behaviour of the predatory larvae of R. fasciata and P. conspersa resulted in a switched prey composition, whereas a reduction in the daily feeding activity was not observed. That was supposed because of changes in the activity pattern by the predator R. fasciata or the changed prey availability for P. conspersa in the fish reach. A general reduction in feeding activity or animal food proportion of the omnivores was not assessed in the presence of fish. In contrast, the relations between the resources switched to a more variable utilisation in the fishless reach. The annual total consumption of invertebrate predators and omnivores was decreased by 20-50% in the fish reach, mainly caused by fish induced biomass reduction. The missing fish consumption could be at least balanced by higher invertebrate consumption in the fishless reach. Contrary, the prey specific consumption of invertebrate predators changed by behavioural-induced switch in the prey composition between the stream reaches. Therefore, a higher predation pressure on detritus feeding species (e.g Diptera) was found in the fishless reach, but not on the supposed key species of the potential biomanipulation (e.g. grazing mayflies). Due to the high importance of invertebrate predation in stream food webs, the aim of biomanipulation can only be reached by considering the populations of predatory invertebrates. Controlling the biomass of suitable benthivorous fish to an optimum (relatively high) level could sufficiently reduce the impact of invertebrate predators leading to an indirect enhancement of grazing species.

This study addresses the regulation of large river phytoplankton by climate-related drivers with the help of three different approaches, i.e. analyses of long-term data and spatial dynamics (longitudinal samplings) as well as mathematical modeling. The central hypothesis is that discharge has a dominant role among climate-related variables which strongly alters phytoplankton biomass development. A multi-factorial statistical analysis on the basis of long-term data (1990 – 2009; 1994 – 2009) from two measuring stations of the rivers Rhine and Elbe revealed that discharge conditions and light availability were the main driving forces regulating phytoplankton spring bloom dynamics. For the Rhine, a trend towards an earlier occurrence of the spring bloom event and a decrease in seasonal mean phytoplankton biomass could be detected, whereas for the Elbe no shift in the timing of the spring bloom and a tendency towards increasing seasonal mean phytoplankton biomass was found. Longitudinal sampling campaigns served to analyze the spatial plankton development on a short-term scale. River-internal growth and loss processes, as well as import mediated by tributaries were examined. Four longitudinal profiles were realized at different seasons in recent years (2009 – 2011) and it was revealed that tributaries mainly had a diluting impact on plankton densities in the Elbe and provided an additional import of phyto- and zooplankton densities in the Rhine. In the present study, high bivalve abundances were detected in the Rhine, probably leading to river-internal losses of phytoplankton which could compensate phytoplankton production resulting in low phytoplankton concentrations. In the Elbe, low abundances of bivalves and a low benthic grazing pressure prevailed. On the other hand, an unusually low discharge event in spring 2011 in the Rhine demonstrated that loss processes can at times be superimposed by strong phytoplankton production leading to extremely high phytoplankton biomasses and chlorophyll a values. Hence, despite the observed long-term trend of decreasing chlorophyll values in the last two decades, extreme environmental conditions can provoke regime shifts with exceptional phytoplankton mass developments. To assess the potential impacts of future climate change on water quality, the water quality simulation model QSim was used to establish a model for the free-flowing part of the Rhine. The modeling approach was implemented by changing the hydrological and climatologic input data according to different climate projections for the near (2021 – 2050) and the far future (2071 – 2100). The model results indicated a weak response of phytoplankton biomass in the Rhine towards altered climatic conditions, including discharge reductions and water temperature increases. The study suggests that changes in discharge rather than water temperature mediate climate change effects on large river phytoplankton. However, the effects are river specific as a consequence of system specific differences in main control mechanisms (e.g. ‘bottom-up’ versus ‘top-down’). / Anhand von drei verschiedenen Ansätzen analysiert die vorliegende Arbeit die Regulierung von Phytoplankton in großen Flüssen durch klimabedingte Faktoren: Auswertung von Langzeitdaten, räumliche Dynamik (fließzeitkonforme, longitudinale Beprobungen) und mathematische Modellierung. Die zentrale Hypothese ist, dass Abfluss eine dominante Rolle unter den klimabedingten Faktoren spielt und die Phytoplanktonbiomasse stark beeinflusst. Eine multifaktorielle statistische Analyse basierend auf Langzeitdaten (1990 – 2009; 1994 –2009) von zwei Stationen der Flüsse Rhein und Elbe zeigten, dass hauptsächlich Abflussbedingungen und Lichtverfügbarkeit die Antriebskräfte bei der Regulierung der Phytoplanktonfrühjahrsblüte darstellten. Während sich am Rhein ein Trend hin zu einem früheren Auftreten der Frühjahrsblüte und einer Abnahme der mittleren Phytoplankton-biomasse während der Vegetationsperiode zeigte, konnte für die Elbe keine zeitliche Verschiebung der Frühjahrsblüte festgestellt werden und mittlere Phytoplanktonbiomassen zeigten hier eine steigende Tendenz. Longitudinale Fließzeitbeprobungen dienten zur Analyse der kurzfristigen räumlichen Entwicklung des Planktons. Interne Produktions- und Verlustprozesse, sowie der Eintrag durch Zuflüsse wurden untersucht. Vier longitudinale Profile wurden zu unterschiedlichen Jahreszeiten der letzten Jahre (2009 – 2011) realisiert und es wurde gezeigt, dass die Nebenflüsse der Elbe vorwiegend einen Verdünnungseffekt auf die Planktondichten des Hauptstromes hatten, während sie für den Rhein einen wichtigen zusätzlichen Eintrag von Phyto- und Zooplankton darstellten. In der vorliegenden Arbeit wurden hohe Muscheldichten im Rhein gefunden, die möglicherweise zu hohen internen Planktonverlusten durch Fraß beigetragen haben, und somit zu niedrigen Phytoplankton-konzentrationen geführt haben könnten. In der Elbe waren die Muscheldichten dagegen gering und somit war auch der benthische Fraßdruck niedriger. Auf der anderen Seite zeigte ein ungewöhnlich niedriges Abflussereignis im Frühjahr 2011 am Rhein, dass diese Verlustprozesse zeitweise von starker Phytoplanktonproduktion überlagert werden können und dadurch extrem hohe Phytoplanktonbiomassen und Chlorophyllwerte entstehen können. Demzufolge können trotz der Beobachtung eines langfristigen abnehmenden Trends in den Chlorophyllgehalten während der letzen zwei Jahrzehnte extreme Umweltbedingungen einen Regime-shift mit außergewöhnlichen Massenentwicklungen des Phytoplanktons hervorrufen. Um den möglichen Einfluss des zukünftigen Klimawandels auf die Gewässergüte abzuschätzen, wurde mithilfe des Gewässergütesimulationsmodells QSim ein Modell für den frei fließenden Abschnitt des Rheins erstellt. Für den Modellierungsansatz wurden die hydrologischen und klimatologischen Eingangsdaten entsprechend der verschiedenen Klimaprojektionen für die nahe (2021 – 2050) und ferne Zukunft (2071 – 2100) verändert. Die Modellergebnisse zeigten, dass sich Änderungen in den klimatischen Bedingungen, einschließlich Abflussreduktion und Wassertemperaturanstieg, nur geringfügig auf die Phytoplankton¬biomasse des Rheins auswirkten. Die vorliegende Arbeit deutet darauf hin, dass Klimawandeleffekte eher durch Änderungen der Abflussverhältnisse auf das Phytoplankton in großen Flüssen wirken als durch Änderungen der Wassertemperatur. Der Effekt ist jedoch flusssystemspezifisch, da die Auswirkungen von systemspezifischen Unterschieden in den Hauptkontrollmechanismen gesteuert werden (z.B. ‚Bottom-up’ versus ‚Top-down’).

In South Africa water is recognized as a crucial element in the battle against poverty, the cornerstone of prosperity, and a limiting factor to growth. The National Water Act 36 of 1998 recognizes that basic human and environmental needs should be met and that the use of water in all aspects must be sustainable. The Crocodile River (East) is situated in the north east of the Republic of South Africa and it is recognized as a stressed catchment in South Africa. The main impacts are domestic, industrial, agricultural, mining and afforestation activities. These activities pollute the river by discharging effluent as well as seepage from areas that support mining and intensive agriculture in to the river. The river catchment has been a center of research studies for many scientists either focusing on water quality or biological indicators separately. The aim of study was to determine the present ecological condition and the health of the Crocodile River. The objectives were to determine water quality status, identify possible sources of pollution and assess the spatial and temporal trends in ecological state. Fourteen monitoring sites were selected from the Crocodile River and its tributaries. The macro-invertebrates data were collected using the SASS 5 protocol and fish were collected using an electroshocker- catch and release method during high and low flow conditions of the year 2013. Water quality data was obtained by sampling using a polyethylene bottle from different sites within the Crocodile River and its tributaries from September 2012 until August 2013. The samples were analyzed by Mpumamanzi laboratory in Nelspruit and Waterlab in Pretoria. Additional water quality data was obtained from the Department of Water Affairs. Multivariate statistical methods were used to analyze all the data obtained. The multivariate statistical methods indicated that fish and macro-invertebrates species abundance, richness and evenness increase with the river flow distance downstream. Water temperature was one of the leading environmental variables for the structuring of fish and macro-invertebrates assemblage in the Crocodile River and its tributaries. A group formation of site during high and low flow condition by the Bray Curtis similarity and NMDS ordination indicated that many sites share similar macro-invertebrates or fish species. The one way ANOVA analysis indicated that there was no significance difference between macro-invertebrates richness and abundance during both flow conditions but there was a significance difference in fish richness and abundance between the two flow conditions. The PCA indicated that sodium has the highest physico-chemical impact amongst the physico-chemical parameters in the bi-plot followed by ammonium and nitrate. A correlation of physico-chemical parameters such as chlorine, total dissolved solid, electrical conductivity, sulphate and pH was observed. The levels of total dissolved solids and electrical conductivity were found to increase longitudinally as the river flows downstream. The dominance of single species within the macro-invertebrates and fish communities was an indication of imbalance of the communities within the sites. The presence of the macro-invertebrate family Beatidae and the fish species Chiloglanis pretoriae at sites CR3 and CR4 indicates a good water quality in the upper reaches during low flow condition as these species are sensitive to changes in water quality, while the presence of the macro-invertebrate family Pleidea and fish species Barbus viviparus at sites CR10 and KR1 during low flow condition indicated possible water pollution as these species tolerate changes in water quality and this was linked to the discharge of effluent from industrial, abandoned mines and run-offs from agricultural activities in the downstream reaches of the river. The low flow condition was dominated by sensitive species especially in the upper reaches than during high flow condition. The macro-invertebrates assessment index indicated that during low flow condition the Crocodile River was mostly at ecological class B (largely natural with few modification) above the Kwena dam, but from downstream of the dam the ecological category was in C class (moderately modified), while its tributaries are in ecological category B (largely natural with few modification). The fish response assessment index indicated that the ecological category for fish was mostly at C class (moderately modified) in the Crocodile River. The changes in macro-invertebrates communities and fish in the Crocodile River were believed to be associated with change of water quality and habitat modification due to flow modification. Agricultural activities in the upper reaches and a combination of industrial and mining activities in the middle and lower reaches of the Crocodile River were believed to be the sources of pollution that results in the change of water quality, fish and macro-invertebrates assemblage in the Crocodile River. Investing in the health of the Crocodile River is important for many Mbombela citizens and river dwellers as they rely on the functioning of the river for survival. / Environmental Sciences / M. Sc. (Environmental Science)

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The primary aim of this study was to assess and compare the ecological integrity of the Lourens, Palmiet and Hout Bay Rivers (South Western Cape, South Africa) by examining the macroinvertebrate community structure at a series of representative sampling sites along the course of each river, using the South African Scoring System - Version 5 (SASS-5) rapid bioassessment method. Secondary aims included an examination of the effects of seasonal variability, biotope availability and site-specific environmental variables on the macroinvertebrate community structure at sampling sites, as well as the preliminary testing of the Integrated Habitat Assessment System (IHAS) for aquatic macroinvertebrates. According to results obtained, the ecological integrity of sampling sites in the Mountain Stream Zone of the three rivers was consistently good. The Hout Bay River in the upper portions of the Orange Kloof Reserve was particularly near-pristine, with this area having been identified in this study as a potential biodiversity ‘hot-spot’ for aquatic macroinvertebrates. Downstream of the Mountain Stream Zone, there was a significant deterioration in the ecological integrity of all three rivers due to a number of probable causes. Results based on recorded SASS Scores and Average Score per Taxon (ASPT) values, using ‘biological bands’ generated from reference sites in the South Western Cape, were generally similar to and supported by the corresponding multivariate analyses undertaken. From the results of the various analyses undertaken in this investigation and some of the problems encountered in interpreting the data, a number of recommendations are made regarding future bioassessment studies based on the SASS within the national River Health Programme (RHP). To test the IHAS, secondary data were obtained from reference sites in the Mpumalanga and Western Cape Provinces of South Africa. Assuming that SASS Scores at reference sites are the highest scores attainable, one would expect to find a positive relationship between SASS Scores and IHAS scores at reference sites. The assumption in this investigation was that this relationship should be linear. Non-parametric correlation analyses were undertaken between SASS-4/5 Scores and IHAS scores, using Kendall’s Rank-correlation Coefficient (τ), with separate analyses undertaken for different geomorphological zones and biotope groups. Correlations between SASS Scores and IHAS scores were generally weak (τ-values mostly < 0.3) and unsatisfactory, with no significant correlations (p < 0.05) for two-thirds of the data sets analysed and a wide degree of scatter generally observed amongst data points in respective scatter plots. The performance of the IHAS varied between geomorphological zones and biotope groups, with the Foothill: Gravel-bed Zone in Mpumalanga showing the best results, particularly when the stones-in-current biotope group was analysed separately. Further testing of the IHAS is required to confirm its relative performance in different bioregions/ecoregions, geomorphological zones and biotope groups, which should be undertaken as a priority research area within the RHP. Unsuccessful attempts to test the IHAS by means of multiple regression analyses were undertaken, suggesting that such techniques should be avoided in further testing of the IHAS. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om die ekologiese toestand van die Lourens-, Palmiet- en Houtbaairiviere (Suidwes Kaap, Suid Afrika) te bepaal en te vergelyk deur die bestudering van die makroinvertebraatgemeenskapstruktuur by verteenwoordigende monsterpunte langs die riviere, met gebruik van die “South African Scoring System” – Weergawe 5 (SASS-5) snelle biologiese bepalingsmetode. Sekondêre doelwitte het die bepaling van die gevolge van seisoenele veranderlikheid, biotoop beskikbaarheid en ligging-bepaalde omgewingsveranderlikes op die makroinvertebraatgemeenskapstruktuur by monsterpunte ingesluit, asook die inleidende toetsing van die “Integrated Habitat Assessment System” (IHAS) vir watermakroinvertebrate. Volgens die resultate verkry, was die ekologiese toestand van monsterpunte in die Bergstroomsone van die drie riviere konsekwent goed. Die Houtbaairivier in die boonste gedeelte van die Oranjekloofreservaat was veral feitlik onversteurd en hierdie streek is in die studie as ‘n potensiaal biodiversiteit “hot-spot” vir watermakroinvertebrate geidentifiseer. Stroomafwaarts van die Bergstroomsone was daar ‘n beduidende verswakking in die ekologiese toestand van al drie riviere, as gevolg van ‘n aantal moontlike oorsake. Resultate gebaseer op bepaalde “SASS Scores” en ‘Gemiddelde Waarde per Takson’ (“Average Score per Taxon” - ASPT) waardes, met gebruik van ‘biologiese bande’ wat van verwysingsmonsterpunte in die Suidwes Kaap afgelei is, was oor die algemeen soortgelyk aan en gestaaf deur die ooreenstemmende multiveranderlikke (“multivariate”) statistiese analises wat gedoen is. Uit die resultate van die verskeie analises wat in hierdie ondersoek gedoen is en sommige van die probleme wat in die dataverklaring gevind is, is ‘n aantal aanbevelings gemaak met betrekking tot toekomende biologiese bepalingstudies vir die nasionale Riviergesondheidsprogram (“River Health Programme” - RHP) wat op die SASS gebaseer is. Om die IHAS te toets is sekondêre data van verwysingsmonsterpunte in die Mpumalanga en Wes Kaap Provinsies van Suid Afrika verkry. As aangeneem word dat die “SASS Scores” by verwysingsmonsterpunte die hoogste moontlike tellings is wat bereik kan word, sou ‘n positiewe verwantskap tussen “SASS Scores” en IHAS tellings by verwysingsmonsterpunte verwag word. Die veronderstelling in hierdie studie was dat dié verwantskap lineêr moet wees. Nie-parametriese korrelasieanalise tussen “SASS-4/5 Scores” en IHAS tellings is gemaak, deur gebruik van Kendall se Rangkorrelasiekoëffisiënt (τ), met afsonderlike analises vir verskillende geomorfologiese sones en biotoopgroepe verrig. Korrelasies tussen “SASS Scores” en IHAS tellings was algemeen swak (τ-waardes < 0.3) en onbevredigend, met geen beduidende korrelasies (“p” < 0.05) vir twee-derdes van die datastelle wat geanaliseer is nie en ‘n wye verspreiding tussen datapunte in die onderskeie “scatter plots” wat waargeneem is. Die funksionering van die IHAS was verskillend tussen geomorfologiese sones en biotoopgroepe. Die beste resultate is vir die Voorheuwel: Gruisbeddingsone in Mpumalanga verkry, veral indien die klippe-in-stroom biotoopgroep afsonderlik geanaliseer is. Verdere toetsing van die IHAS is nodig om die relatiewe funksionering in verskillende biostreke/”ecoregions”, geomorfologiese sones en biotoopgroepe te bevestig en dit behoort voorangs te geniet binne die RHP. Pogings om die IHAS deur middel van veelvoudige regressie analise te toets het misluk, wat aandui dat sulke tegnieke vermy moet word in verder toetsing van die IHAS.