Dissertationen zum Thema „Riverine imputs“

Les zones côtières représentent un enjeu majeur en termes d’activités économiques et de préservation d’un bon état chimique et écologique du milieu naturel. Si à l’échelle globale (mer ou océan) les flux de contaminants notamment les éléments traces métalliques et métalloïdes (ETMM) sont relativement bien étudiés et décrits, ce n’est pas le cas des zones plus enclavées à une échelle plus locale. La rade de Toulon qui possède une morphologie semi-fermée est entourée d’une métropole importante (450 000 habitants) avec une forte activité anthropique (premier port militaire en France, ports civils, transport de passagers, aquaculture, …). Ces activités présentes et passées comme la deuxième guerre mondiale, ont conduit à une forte contamination sédimentaire ainsi qu’un fort gradient de concentrations en ETMM entre le Sud de la grande rade, connecté à la mer Méditerranée, et les parties les plus enclavées de la petite rade. Dans ce contexte de zone côtière contaminée, l’objectif de ce travail est d’évaluer la contribution des apports fluviaux et atmosphériques en ETMM à la rade de Toulon. Le mode d’échantillonnage proposé associant des capteurs de terrain, des pièges à particules et des prélèvements ponctuels différenciés entre l’étiage et la crue ont permis d’obtenir une chronique d’apports en ETMM prenant en compte la variabilité météorologique. Les résultats montrent que les apports en ETMM par les rivières (Las et Eygoutier) sont prépondérants durant les crues et dans la fraction particulaire et, sont plus particulièrement préoccupant pour le cuivre et le zinc qui dépassent les seuils réglementaires. Dans le Las, l’apport prépondérant reste cependant le cuivre dissous durant les crues. Dans l’Eygoutier, les valeurs obtenues sont inférieures aux mesures précédemment réalisées en 2004. Les apports en étiage sont largement minoritaires et des teneurs élevées en cadmium et mercure dans les particules ont été mesurées sans pouvoir identifier leur source. Les apports atmosphériques en ETMM sont dominés par la fraction particulaire avec des teneurs dépassant les seuils réglementaires d’un facteur 2 à 4 en cuivre, plomb et zinc. A l’échelle de la rade, les apports fluviaux restent supérieurs aux apports atmosphériques pour tous les ETMM. En faisant un bilan sur l’ensemble de la rade et en prenant en compte les autres sources existantes (ports, ruissellement, stations d’épuration, diffusion sédimentaire), la contribution des apports fluviaux et atmosphériques est estimée à 4 % pour le mercure, autour de 30 % pour le cuivre et le cadmium et près de 70 % pour le plomb et le chrome. Le bilan des flux d’ETMM dans la rade conduit à décrire la rade comme une source de contamination pour la mer Méditerranée. Ceci est confirmé par l’export net calculé pour le plomb, le mercure ou le cadmium tandis que pour le cuivre et le nickel des sources manquantes restent à être déterminées pour confirmer l’hypothèse. Pour le zinc et l’arsenic, la trop grande variabilité empêche de conclure car, ces estimations nécessitent d’être affinées
Coastal areas represent a major issue in terms of economic activities and preservation of a good chemical and ecological status of the natural environment. If on a global scale (sea or ocean) the flow of contaminants, especially trace metals and metalloids (TMM) are relatively well studied and described, this is not the case for more enclosed areas on a more local scale. The Toulon Bay, which has a semi-closed morphology, is surrounded by a large urban area (450 000 inhabitants) with a strong anthropic activity (first military port in France, civil ports, passenger transport, aquaculture, ...). These present and past activities, such as the Second World War, have led to a strong sedimentary contamination as well as a strong gradient of concentrations in TMM between the South of the large bay, connected to the Mediterranean Sea, and the most enclosed parts of the small bay. In this context of contaminated coastal zone, the objective of this work is to evaluate the contribution of the fluvial and atmospheric contributions in TMM to the Toulon Bay. The proposed sampling method associating field sensors, particle traps and punctual sampling differentiated between base flow and flood allowed to obtain a chronicle of TMM inputs considering the meteorological variability. The results show that the inputs of TMM by the rivers (Las and Eygoutier) are preponderant during floods and in the particulate fraction and are more particularly worrying for copper and zinc which exceed the regulatory thresholds. In the Las, the preponderant contribution remains however the dissolved copper during the flood. In the Eygoutier, the values obtained are lower than the measurements previously carried out in 2004. Base flow inputs are largely in the minority and high levels of cadmium and mercury in the particles were measured without being able to identify their source. Atmospheric inputs of TMM are dominated by the particulate fraction with levels exceeding the regulatory thresholds by a factor of 2 to 4 for copper, lead and zinc. At the bay scale, river inputs remain higher than atmospheric inputs for all the TMM. By making a balance on the whole of the bay and by considering the other existing sources (ports, runoff, wastewater treatment plant, sedimentary diffusion), the contribution of river and atmospheric inputs is estimated at 4% for mercury, around 30% for copper and cadmium and nearly 70% for lead and chromium. The balance of TMM inputs in the bay leads to describe the bay as a source of contamination for the Mediterranean Sea. This is confirmed by the net export calculated for lead, mercury, and cadmium, while for copper and nickel missing sources remain to be determined to confirm the hypothesis. For zinc and arsenic, too much variability prevents conclusions being drawn, and these estimates need to be refined

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Due to anthropogenic activities, aquatic ecosystems are being rapidly modified in the entire world. The negative impact of pollutants, changes in the hydrology of the basin and changes in habitat, or introduction of exotic species, among others, result in the loss of water quality and difficulty in maintaining the integrity of these ecosystems. These changes, significantly affect the fish populations, causing a reduction in availability or even the disappearance of species that are not tolerant to the new environmental conditions. Consequently, fishermen who depend on resources from the aquatic environment can no longer subsist on fishing, which contributes to the loss of empiric knowledge and also in quality of life. The Gramame River, located in the state of Paraiba, Brazil, drains suburban areas of the region of João Pessoa, including its industrial district. As a result it receives a large amount of pollutants, particularly over the past 20 years, in addition to domestic sewage and agricultural pesticides, compounded by the introduction of exotic species. Upstream, near the industrial district, the river is surrounded by areas of sugar cane plantation, without riparian vegetation in most of its course. Coastal communities, residents in the water basin for decades, accompanied the whole process of degradation of the river water quality, now restricted in use by these communities. In this perspective, this study aimed to: (a) analyze the composition of the ichthyofauna in lotic and lentic environments along the basin of the Gramame River, comparing it with previous data in order to identify possible changes over time, (b) analyze the environmental perception from two riverine communities (Gramame and Mituaçu), their perceived changes in the river and fishing due to anthropogenic actions, and (c) relate the distribution of fish with the water quality (phosphorous and nitrogen nutrients). To obtain the data in the communities, a combination of qualitative and quantitative methods was used. The qualitative methods consisted of semi-structured interviews, snowball method and participant observation. The data were analyzed based on the model of unifying the various individual competences. On the other hand, quantitative data were statistically analyzed. Thirty eight fishermen were interviewed in both communities, of both genders, aged between 24 and 75 years. The ichthyofauna was collected with several fishing gear (fishing nets, fish traps, gererê and covos), always taking into account the physiographic and physiognomic peculiarities of each of the sampling points. The data for fish species were submitted to statistical analysis in order to ascertain whether there were significant differences in these parameters between sampling points. Regarding the limnological study, the sampling period were both in winter and summer, and the locations of water collection corresponded to the same sites where fish species where collected. The survey results show significant changes in fish fauna, especially with regard to the emergence of exotic species, which are now dominant in certain parts of the basin, with potential impacts to native fish fauna. It was also found that the fishermen noticed the differences in ichthyofauna and in the river. Despite the observed impacts, this environment is still important economically and socially, to promote the livelihood of many families. From the results obtained in this work it is concluded that there is urgency in formulating strategies for the sustainable use of this basin, integrating social, economic and environmental, in order to promote, among other benefits, the survival of fishing communities that depend on this the ecosystem.
Em virtude das ações antropogênicas, ecossistemas aquáticos estão sendo rapidamente alterados em todo o mundo. O impacto negativo de poluentes, mudanças na hidrologia da bacia e modificações no habitat, ou mesmo introdução de espécies exóticas, entre outras causas, resultam na perda de qualidade da água e dificultam a manutenção da integridade desses ecossistemas, além de afetar de forma significativa as populações de peixes, causando a redução nos estoques, ou mesmo o desaparecimento de espécies que não são tolerantes às novas condições ambientais. Consequentemente, pescadores artesanais que dependem dos recursos dos ambientes aquáticos, não podem mais subsistir da pesca, o que contribui para a perda do conhecimento empírico e para a diminuição da qualidade de vida. O Rio Gramame, localizado no estado da Paraíba, Brasil, passa por áreas periurbanas da região de João Pessoa, incluindo o seu distrito industrial. Consequentemente vem recebendo uma grande carga de poluentes, particularmente ao longo dos últimos 20 anos, além de efluentes domésticos e pesticidas agrícolas, agravados pela introdução de espécies exóticas. A montante do distrito industrial, o rio é rodeado por áreas de plantio de cana- de- açúcar, sem mata ciliar na maior parte do seu percurso. As comunidades ribeirinhas, residentes há décadas na bacia hidrográfica, acompanharam todo o processo de degradação da qualidade da água do rio, atualmente de uso restrito por estas comunidades. Nesta perspectiva, este estudo objetivou: (a) analisar a composição da ictiofauna em ambientes lóticos e lênticos ao longo da bacia do Rio Gramame, comparando-a com dados anteriores a fim de identificar possíveis modificações ao longo do tempo; (b) analisar a percepção ambiental junto a duas comunidades ribeirinhas (Gramame e Mituaçu) acerca das alterações observadas no rio e na pesca em decorrência de ações antropogênicas e, (c) relacionar a distribuição de peixes com a qualidade da água (nutrientes fosfatados e nitrogenados). Para obtenção dos dados junto às comunidades utilizou-se uma combinação de métodos qualitativos e quantitativos. Dentre os métodos qualitativos, destacam-se: entrevistas semi-estruturadas, bola de neve ( Snow Ball ) e observação participativa. Os dados obtidos foram analisados com base no modelo de união das diversas competências individuais. Por outro lado, os dados quantitativos foram analisados estatisticamente. Foram entrevistados 38 pescadores em ambas as comunidades, de ambos os sexos, com idades entre 24 e 75 anos. A ictiofauna foi coletada com o auxílio de diversas artes de pesca (tarrafa, rede malhadeira, gererê e covos), sempre levando em consideração as peculiaridades fisiográficas e fisionômicas de cada um dos pontos amostrais. Os dados referentes à ictiofauna foram submetidos a análises estatísticas, com o objetivo de averiguar se houve diferenças significativas nos parâmetros analisados entre os pontos amostrais. Em relação ao estudo limnológico, amostras de água foram coletadas no período chuvoso e de estiagem, e os locais de coleta corresponderam aos da ictiofauna. Os resultados da pesquisa evidenciaram alterações significativas na ictiofauna, principalmente no que diz respeito ao surgimento de espécies exóticas, que hoje são dominantes em determinados pontos da bacia, com impacto potencial para a ictiofauna nativa. Constatou-se também que os pescadores perceberam as diferenças ocorridas na ictiofauna e no rio, e que apesar dos impactos observados, esse ambiente continua sendo importante social e economicamente, por promover o sustento de muitas famílias. Conclui-se, a partir dos resultados obtidos neste trabalho, que há urgência na formulação de estratégias que permitam o uso sustentável dessa bacia, integrando fatores sociais, econômicos e ambientais, de modo a promover, dentre outros benefícios, a sobrevivência de comunidades que dependem da pesca neste ecossistema.

Thesis (Ph. D.)--University of California, Riverside, 2010.
Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed May 18, 2010). Includes bibliographical references. Also issued in print.

Les cours d’eau font l’objet de prescriptions législatives encourageant leur restauration, et l’arasement de barrages est une des solutions utilisées actuellement en France pour y parvenir. La végétation riparienne participe à l’intégrité et à la stabilité des systèmes fluviaux, Elle est donc une composante majeure à évaluer dans le cadre des actions de restauration .Les objectifs de la thèse sont d'analyser la dynamique de colonisation des berges exondées à court terme dans le contexte de l’arasement des barrages de la Sélune (Normandie) et de développer des indicateurs de suivi à long terme des zones ripariennes. Dans un premier temps, une analyse des dynamiques de colonisation aux échelles intra et interannuelles réalisée à l’aide d’images drone et de relevés terrain a révélé la pertinence de l’utilisation d’images drones pour cartographier la végétation, ainsi que des dynamiques successionnelles rapides, avec un potentiel de restauration passive et de stabilisation des sédiments. Dans un second temps, l’analyse de nuages de points LiDAR en trois dimensions acquis en hiver et en été a montré la complémentarité des deux dates d’acquisition pour cartographier des indicateurs de statut des ripisylves à large échelle tels que les essences principales, l’ombrage ou la densité de strates herbacées et arbustives. Ces résultats permettent de discuter les dimensions méthodologiques et opérationnelles de l’utilisation des approches par télédétection pour le suivi des ripisylves
Rivers are the object of legislation encouraging their restoration, and dam removal operations represent one of the solution to achieve it in France. Riparian vegetation plays a fundamental role in stabilizing and maintaining fluvial systems, being at the interface between terrestrial and aquatic environments. It is therefore a very important component which has to be evaluated in river restoration operations. One of the consequences of dam removal on riparian vegetation is the colonization of the dewatered sediments in the reservoir. The objective of the thesis are to define short term colonization dynamics of vegetation in context of dam removal (Sélune River, Normandy), and to develop long term indicators for the monitoring of riparian vegetation. First, an analysis of intra and interannual colonization dynamics revealed the potential of using drone images to map riparian vegetation, and fast successional dynamics with high passive restoration and sediment stabilization potential. Secondly, the analysis of 3D point clouds extracted from LiDAR data acquired in winter and summer highlighted the complementarity of the two acquisition dates to map indicators of riparian status at large scale, such as main riparian species, shading or density of herbaceous and shrubby strata. These results make it possible to discuss the methodological and operational dimensions of the use of remote sensing approaches for the monitoring of riparian vegetation

Inter-Basin-Water Transfers significantly reduce flow and sediment regimes to the downstream ecosystem effecting differential channel adjustment at various locations. It is not known how macroinvertebrates adjust to flow regulation, either spatially or temporally, because research is lacking into how morphological adjustment affects benthic habitat. Feedback mechanisms that initiate the adjustment process must first be identified, then the effect on benthic habitat becomes apparent, thus, providing a link to macroinvertebrate response. Since regulation there has been a 95% reduction in flow volume, a complete downward shift in both the flow duration and flood frequency curves and a 194% increase in flow constancy compared to the pre- dam period. Furthermore, Jindabyne Dam traps 99.9% of the total incoming sediment load. Upstream of the tributary the dominant river response was accommodation adjustment with subsequent contraction of the river channel. Associated feedback mechanisms were ?armouring? and vegetation encroachment. Downstream of the tributary response was more complex, with channel contraction through aggradation and specifically the formation of a tributary mouth bar and fan, mid channel lobate bar, transverse bar and in-channel bench. Associated feedback mechanisms were interactions between vegetation and sediment; channel morphology, flow and sediment distribution; and sediment distribution, flow and channel morphology. These processes have had site specific and reach scale impacts on benthic habitat. Macroinvertebrate response to flow regulation was habitat specific (riffle or edge) and seemed to correspond to either site, or reach scale morphological adjustment, whereas, flow constancy seemed to affect edge macroinvertebrates throughout both reaches. Spatially, macroinvertebrates have not adjusted to the post- dam flow regime and temporally, macroinvertebrates have not recovered 30 years after the closure of Jindabyne Dam. How physical processes change habitats and how these impact on a river?s ecology and at what scale, are important considerations in river management.

Student Number : 9907276D - MSc Dissertation - School of Animal, Plant and Environmental Sciences - Faculty of Science
The broad aim of this study was to measure the ecosystem repair of the Sabie River (which traverses through both the grassland and savanna biomes) riparian environment in Mpumalanga, South Africa, in response to the clearing of alien plants by the Working for Water (WfW) alien plant clearing programme. This was done in order to assess the effectiveness of the WfW clearing on the Sabie River riparian plant community composition and associated environmental factors. Although “effectiveness” can be assessed in various ways, in this study it included determining whether there was a reduction in the invasion intensity (defined as the percentage aerial cover of woody alien plants) after clearing. This broad aim was achieved by studying the impacts of the WfW alien plant clearing programme, as well as the invasion of alien plants, on the plant species composition, diversity and vegetation structure of riparian ecosystems on the Sabie River. Hence, in 2005 40 modified Whittaker nested plots were sampled. The impacts on the Sabie River riparian environment were also assessed by measuring various environmental variables that are likely to change as a result of clearing, such as the ground cover (percentages of exposed soil, rock, litter, herbaceous vegetation and grass), as well as various soil chemical and physical properties. Twenty plots were surveyed along the Sabie River in the Hazeyview region (savanna biome), ten in the Sabie region (grassland biome) and ten in the Graskop region (grassland biome). The response of the Sabie River riparian community to invasive alien plant clearing by WfW (and the alien plant invasion itself) was also assessed over time, by comparing the 2005 study with one done in 1996, which used the same plots. In 2005, a cumulative total of 282 species were found, 222 (79%) of which were indigenous and 60 (21%) alien. The grassland sites had a higher cumulative total of 222 species compared with the 171 species in the savanna sites. A total of 112 (39%) species were common between the biomes, 86 (30%) of which were indigenous and 26 (9%) alien. At the 1000 m2 scale, the indigenous species richness (32.4 ± 1.4 (S.E.)) was significantly higher than the alien species richness (12.0 ± 0.5) (P < 0.001). Of the 60 alien species, 17 (28%) were shrubs and 15 (25%) trees. The grassland sites were more species rich at the 1000 m2 scale (48.8 ± 1.8) and diverse at the 100 m2 scale (Simpson’s index of alpha diversity of 0.90 ± 0.01) than the savanna sites (species richness of 40.0 ± 2.1 and alpha diversity of 0.85 ± 0.02; P = 0.003 for species richness and P = 0.04 for alpha diversity). The Sabie sites were more species rich at the 1000 m2 scale (52.6 ± 2.8) than the Graskop sites (45.0 ± 1.4) (P = 0.12). The higher species richness in the Sabie region contributed to the higher total species richness in the grasslands relative to the savanna sites. At the 1000 m2 scale, the overall beta diversity (Sorenson’s coefficient of community) between the biomes was 0.57, and the species complementarity (the Marczewski-Steinhaus distance) between the biomes was 0.60, indicating that the biomes were not that similar in terms of species composition. Even though the grassland was more rich and diverse in terms of species than the savanna, the overall relative abundances of plant species in each biome was very similar (species evenness (Simpson’s measure of evenness), at the 100 m2 scale, of 0.52 ± 0.03 in the grassland and 0.51 ± 0.03 in the savanna; P = 0.74). The savanna tended to have a higher degree of invasion intensity (aerial cover of woody alien plants of 34.4 ± 4.6% compared to 29.4 ± 4.5% in the grassland; P = 0.44), possibly due to its position lower in the catchment, and hence a sink for upstream alien plant propagules. It was hypothesized that higher plant species richness and/or diversity should enhance community resistance to alien plant invasions, in both the grassland and savanna biomes. In the Sabie (grassland) region, there was a negative correlation between the indigenous and alien species richness, thus indicating that the Sabie region plant community may have been more resistant to the invasion of alien plants than the other two regions. Therefore, the hypothesis was not rejected for the Sabie region. On the other hand, in the Graskop (grassland) and Hazeyview (savanna) regions, there were positive correlations between the indigenous and alien species richness, thus indicating that these plant communities may not have been as resistant to the invasion of alien plants. Therefore, the hypothesis was rejected for both the Graskop and Hazeyview regions. When considering the biome scale, the hypothesis was not rejected as the increase in total species richness with increasing invasion intensity in the grassland (which was more diverse than the savanna) indicated that it may have been more resistant to the invasion of alien plants than the savanna, which had a total species richness that decreased with increasing invasion intensity. In 2005, exposed soil, litter and grass covers tended to be slightly higher in the savanna (14.4 ± 1.6%; 43.5 ± 3.0%; 21.8 ± 1.7% respectively) than in the grassland (12.1 ± 2.5%; 43.2 ± 4.2%; 20.1 ± 2.3% respectively) (P = 0.43, 0.96 and 0.56 respectively). Rock and herbaceous covers were higher in the grassland (4.3 ± 1.6% and 20.3 ± 1.7% respectively) than in the savanna (0.8 ± 0.2% and 19.5 ± 2.2% respectively), but only rock cover was significantly different (P = 0.04) (P = 0.76 for herbaceous cover). These patterns in ground cover may have been a response to the slightly higher invasion intensity in the savanna. The hypothesis that the lower the degree of alien plant invasion, the higher the understorey vegetation cover, which may result in reduced cover of exposed soil and litter, in both the grassland and savanna biomes, was not rejected as the grassland tended to have a lower degree of alien invasion (although not significant), a higher cover of herbaceous vegetation, and corresponding lower covers of exposed soil and litter. The biomes (in 2005) did not differ significantly in soil pH (grassland pH: 4.6 ± 0.1; savanna pH: 4.8 ± 0.1; P = 0.34). However, the grassland soils were generally more fertile than the savanna soils, i.e. higher organic matter (4.5 ± 0.2% versus 3.3 ± 0.4%; P = 0.01) and total nitrogen (0.3 ± 0.02% versus 0.2 ± 0.02%; P = 0.03). The concentrations (mg/l) of most of the nutrients were also higher in the grassland. The lower fertility of the savanna soils may have been related to the higher litter cover of the savanna immobilizing a larger amount of available nutrients than the grassland; another possibility may have been slower rates of soil organic matter decomposition in the slightly cooler (higher altitude) grassland regions. The soils of the grassland sites tended to be more compacted (0.8 ± 0.1 kg/cm2) (but not significantly) than those of the savanna sites (0.7 ± 0.1 kg/cm2) (P = 0.43), and the savanna plots were on significantly steeper ground (12.8 ± 1.7º) than the grassland plots (4.8 ± 1.1º) (P < 0.001), which may have also contributed to lower fertility through greater leaching and erosion losses. From the detrended correspondence analysis (DCA) of the species by plot data, there were no distinct plant communities separating out between the biomes and regions. This is probably because the Sabie River riparian environment essentially supports a riparian forest/woodland, rather than reflecting the species typically found in the adjoining (more upland) grasslands and savannas. Hence, the species composition of the riparian environment was fairly uniform throughout the study area. The canonical correspondence analysis (CCA), which also incorporates the environmental variables, showed that altitude, exposed soil cover, soil pH, organic carbon content and slope steepness were the variables that most closely (and significantly) correlated with the species composition, and two of these variables relate directly to soil fertility, and the other three are indirectly related to soil fertility. Of the original “treatments” of the 1996/1997 study, namely (A) biome (grassland versus savanna), (B) invasion intensity (high (> 50%) versus low (< 50%)), and (C) clearing (cleared versus uncleared), the legacy of the latter two did not persist over time, as there was little or no clear overall relationship between the 1996 and 2005 data when analysed by ANCOVA. The cumulative total species richness sampled in the 40 plots increased from 163 species in 1996, to 282 in 2005 (42% increase). Mean species richness (at the 1000 m2 scale) was 24.1 ± 1.0 in 1996 and 44.4 ± 1.5 in 2005 (P < 0.001). Trees increased from 28 species in 1996 to 46 in 2005 (39% increase), shrubs from 44 to 82 (46%), herbaceous plants from 71 to 121 (41%), and grasses from 20 to 33 (39%). However, even though the species richness of each growth form increased over time, the proportion of each growth form remained approximately the same, i.e. in 1996, 17% of the species were trees, 27% shrubs, 44% herbaceous and 12% grasses; whereas in 2005, 16% were trees, 29% shrubs, 43% herbaceous and 12% grasses. The greatest increase over time was for category 1, 2 and 3 weed species, namely 25 in 1996 to 50 in 2005, a 50% increase. Although mean alpha diversity was higher in 2005 (0.9 ± 0.01 compared to only 0.3 ± 0.03 in 1996 (at the 100 m2 scale); P < 0.001), overall beta diversity over time (a change from 1996 to 2005) was relatively low, indicating a small change in overall species composition, despite the increase in species richness. The invasion intensity (percentage aerial cover of woody alien plants) was similar between the years, i.e. 30.0 ± 4.6% in 1996 and 31.9 ± 3.2% in 2005 (P = 0.73). When comparing the invasion intensity between the three original treatments over time, the invasion intensity of the 1996 grassland and savanna plots remained unchanged. The invasion intensity of the 1996 high invaded plots also remained unchanged over time, however the low invaded plots had a significantly higher invasion intensity in 2005 (P = 0.004). The invasion intensity of the 1996 uncleared plots remained unchanged over time, whereas the cleared plots had a significantly higher invasion intensity in 2005 (P = 0.03). These results clearly show that the legacy of the original invasion intensity and clearing treatments measured in the 1996/1997 study did not persist over time, whereas the inherent differences between the biomes did. The hypothesis that higher plant species richness and/or diversity should enhance community resistance to alien plant invasions was rejected, as both the 1996 and 2005 plant communities were not that resistant to the invasion of alien plants, even though there was a significantly higher species richness and diversity in 2005 than in 1996. It is concluded that because of both the similar growth form composition and invasion intensity over time, the WfW clearing efforts are not succeeding in the primary aim of controlling aliens, particularly woody alien species. However, there was a considerable decrease in the aerial cover of large alien plants, namely (a) alien plants > 5 m decreased from 15.8 ± 4.1% in 1996 to 5.8 ± 1.2% in 2005 (P = 0.02), and (b) those between 2 – 5 m tended to decrease from 13.3 ± 2.8% in 1996 to 11.1 ± 2.4% in 2005 (P = 0.55). However, these decreases were balanced by a considerable increase in the aerial cover of alien plants < 2 m in height, which increased from 3.9 ± 1.0% in 1996 to 15.0 ± 2.1% in 2005 (P < 0.001). This therefore showed that the WfW clearing programme is succeeding, to some extent, in removing most of the larger alien plants but not in controlling the regenerating plants, which recover through post-clearing resprouting and/or newly established seedlings. Exposed soil, rock and litter covers were higher in 2005 (13.3 ± 1.5%; 2.5 ± 0.8%; 43.3 ± 2.5% respectively) than in 1996 (2.1 ± 0.5%; 0.9 ± 0.3%; 16.4 ± 2.7% respectively) (P < 0.001 for soil and litter covers, and 0.07 for rock cover). Herbaceous and grass covers were significantly higher in 1996 (47.8 ± 2.8% and 32.8 ± 2.6% respectively) than in 2005 (20.0 ± 1.4% and 20.9 ± 1.4% respectively) (P < 0.001 for herbaceous and grass covers). These differences in the ground covers between the years may have partially been a response to the major February 2000 flood event, which cleared a large proportion of the vegetation, resulting in much greater rates of erosion and deposition of soils. The WfW clearing operations also removed a significant proportion of the vegetation, and disturbed much that remained, thus modifying the environment. The increase in litter cover may have also been due to the slightly higher invasion intensity in 2005 than in 1996. Soil pH remained unchanged over time (both years had a pH of 4.7 ± 0.1; P = 0.99), indicating that pH was unaffected by the invasion and subsequent clearing of alien plants, as well as the 2000 flood event which moved a tremendous amount of sediment. The hypothesis that the lower the degree of alien plant invasion, the higher the understorey vegetation cover, in both 1996 and 2005, was not rejected as the plots in 1996 had a lower degree of alien invasion (although not significant), a higher cover of herbaceous vegetation, and corresponding lower covers of exposed soil and litter. Along the Sabie River, the alien tree and shrub species with the greatest densities were Rubus cuneifolius (American bramble) (1828 plants/ha), Lantana camara (Lantana) (1760), Solanum mauritianum (Bugweed) (838), Indigofera macrophylla (640), Eucalyptus grandis (Saligna gum) (560), Caesalpinia decapetala (Mauritius thorn) (403), Agrimonia odorata (Agrimonia) (220), Lilium formosanum (St. Joseph’s lily) (218), and Populus x canescens (Grey popular) (125). Focusing the clearing efforts on these species will help to reduce the frequency of re-invasions, reduce costs, and increase ease of clearing. The primary aim of the WfW programme is to increase water supplies by controlling woody alien plants. Therefore, it is concluded that the WfW clearing along the Sabie River has been partially successful, as there has been a significant decrease in the invasion intensity of large (> 5 m) alien trees (which tend to have the highest transpiration rates) over time from 1996 to 2005. In 1996, these large alien trees were represented mainly by Eucalyptus spp. However, the WfW programme was not effective in terms of ecosystem repair, as the invasion intensity increased slightly from 1996 to 2005, largely as a result of the significant increase in the aerial cover of smaller alien shrubs (< 2 m). If left unchecked, these will probably in time result in even higher levels of invasion intensity when the individual plants increase in size and cover. Furthermore, the growth form composition remained relatively unchanged over time, and more than half of the alien species found in 2005 were tree and shrub species. Therefore, little or no ecosystem repair has occurred along the Sabie River. In order to improve the effectiveness of the WfW programme, various detailed recommendations are included, which largely revolve around improvements in follow-up treatments.

L'urbanisation représente une menace majeure pour la biodiversité. Ce mémoire de maîtrise vise à comprendre ses effets sur la composition fonctionnelle et l'homogénéisation biotique dans les forêts riveraines. Des inventaires floristiques ont été réalisés dans 57 forêts riveraines de la région de Montréal. Afin d'étudier la variation de la composition fonctionnelle avec l'urbanisation, des moyennes pondérées de traits par communauté ont été calculées pour les arbres, arbustes et herbacées. Chaque forêt a été caractérisée par des variables relatives au paysage urbain environnant, aux conditions locales des forêts et aux processus spatiaux. Les conditions locales, notamment les inondations, exerçaient une pression de sélection dominante sur les traits. L'effet du paysage était indirect, agissant via l'altération des régimes hydrologiques. La dispersion le long des rivières était aussi un processus important dans la structuration des forêts riveraines. Les changements dans la diversité β taxonomique et fonctionnelle des herbacées ont été étudiés entre trois niveaux d'urbanisation et d'inondation. Alors que l'urbanisation a favorisé une différenciation taxonomique, les inondations ont favorisé une homogénéisation taxonomique, sans influencer la diversité β fonctionnelle. L'urbanisation était l'élément déclencheur des changements de la diversité β, directement, en causant un gain en espèces exotiques et une diminution de la richesse totale dans les forêts très urbanisées, et, indirectement, en entraînant un important turnover d'espèces par l'altération des régimes hydrologiques. Globalement, ces résultats suggèrent que la modification des processus naturels par les activités anthropiques est le principal moteur de changements dans les communautés riveraines urbaines.
Urbanization is a major threat to biodiversity worldwide. This thesis aims at understanding its effects on plant functional composition and biotic homogenization in riparian forests. Floristic inventories were carried out in 57 riparian forests of the Montreal area. To investigate changes in functional composition with urbanization, community weighted means were computed for trees, shrubs and herbs using eight functional traits. Each forest was characterized by variables related to the surrounding urban landscape, local forest conditions and spatial processes. The relative importance of these three subsets on the functional composition was quantified by variation partitioning using redundancy analyses. Local conditions, especially flood intensity, exerted an overriding selection pressure on riparian functional communities. The effect of the landscape was suspected to be indirect, acting on trait patterns likely through alteration of hydrological disturbances in riparian forests. In addition to environmental filtering, dispersal along rivers was also an important process structuring riparian forests. Changes in taxonomic and functional β-diversity for herb species were studied between three urbanization and flood levels. While urbanization led to taxonomic differentiation, flood intensity fostered taxonomic homogenization, both without influence on functional β-diversity. Urbanization was the main trigger for all β-diversity changes, as it directly caused a gain in exotic species and a net species loss in highly urban forests, and indirectly fostered an important species turnover through alteration of the hydrological regime. Overall, these results suggest that the alteration and interruption of natural landscape-scale processes by human activities are major mechanisms underlying changes in urban riparian communities.

Lower reaches of rivers as well as estuaries are regarded as South Africa’s most productive ecosystems due to the important functions such as providing nursery areas and feeding sites for juvenile macro-invertebrate and fish species they perform. Furthermore, ecologically healthy estuaries are not only of critical importance since they facilitate the provision and recirculation of nutrients, they also provide conduits for fish migrations into the fresh water system and act as buffers during floods. In South Africa, these functions are continuously being threatened by residential and/or industrial developments. It is thus essential to determine the ecological integrity (structure and function) of these systems. An Ecological integrity study was carried out on the selected rivers in Kwazulu Natal between 2015 and 2017. This study was assessed in terms of selected abiotic drivers on specific biological responses. The study was carried out according to the guidelines of the ecological determination methodologies and the resource directed measures for aquatic resources as set out by the Department of Water Affairs and Forestry, South Africa. Surveys were carried out during summer and winter seasons. Abiotic and biotic monitoring was carried out at four sites along each estuary. The abiotic component such as sediment composition and physio-chemical properties of the water was analyzed using standard methods. The biotic and abiotic components were analyzed using various indices, where applicable. The ecological integrity of the system can be accessed on the basis of its ability to carry out its natural functions. Results showed the various anthropogenic activities in the upper reaches of each river contributed to the high modified state of some of these rivers’ unacceptable water quality, loss and/or modification of habitat and an altered hydrological pattern due to impacts by agricultural, industrial and domestic uses. The ecosystem services of the lower areas of the rivers under investigation are used extensively through sugarcane agricultural activities and heavy industries works inclusive of sand mining and rural sewage-treatment. These activities affect the ecological integrity of the rivers and ultimately the estuaries. This study aimed at determining the current state of ecological integrity of five selected rivers in KwaZulu Natal and to establish trends between current and historical periods for the evaluation of changing trends in ecological integrity. Abiotic and biotic indicator components were used to ascertain changes in the surrounding environment as well as to determine the ecological integrity of these rivers. Monitoring of water quality, sediment grain size, moisture and organic content as well as habitat state, macro-invertebrates and fish assemblages was undertaken. The following variables water temperature, chemical oxygen demand (COD), electrical conductivity (EC), pH and total alkalinity (TAL) as well as salts, nutrients and toxics were investigated to provide indications as to the state of the water-quality of these rivers. The Target Water Quality Requirements (TWQR) as developed by the Department of Water Affairs and Forestry for domestic use (Volume 1) and Aquatic Ecosystems (Volume 7) were used to evaluate the quality of the water sampled in this study. Historical data obtained from previous studies of similar study areas have also been evaluated. Sediment analyses were performed according to the protocol set out by the United States Environmental Protection Agency. As a result of the abiotic drivers, results showed that the invertebrate reside in modified state. Physio-chemical, geomorphological and hydrological changes in this system resulted in the rivers’ suffering a loss in both biological and ecological function as well as aesthetic value. It is apparent from the above that there is not a need for rehabilitation but also a need for effective and continuous management strategies. These strategies can only be successful if the bio-monitoring of the system includes the effects at both economical and social levels. The water quality of the rivers under this investigation was found to be in a slightly modified state with the majority of water quality parameters falling within the target values. Water quality parameters of the lower Thukela River, not within the required target, was highly elevated and could possibly cause negative impacts on the river functionality. The water quality parameters of Umvoti river, Umdloti river and uMngeni river were seriously modified. The sediment clearly indicated that the organic content of the all the rivers was low and directly relating to the possibility of erosion and transportation taking place in the Rivers. The removal of riparian vegetation by agricultural activities, sand mining and water abstraction contributed to the destruction of the habitats along all these rivers. The South African Scoring System, version 5 (SASS 5), the Macro-invertebrate Response Assessment Index (MIRAI) and multivariate statistical analyses were implemented in order to determine the ecological integrity of the rivers. Results revealed that the SASS 5 integrity classes were generally one class higher than the integrity classes of MIRAI. The Fish assemblage methods used to determine fish samples included electro-narcosis and a 5m wide 12mm meshed seine net. Impacts on the ecological integrity of the Rivers under investigation have been assessed by various sources. To protect the current ecological integrity and further destruction of the rivers under investigation, direct involvement by the relevant authorities is of paramount importance.
Agriculture and Environmental Science
D. Litt. et Phil. (Environmental Science)

Subsistence fishing is impacting on freshwater and marine biodiversity to the extent of extinction of some fish species. These illegal subsistence fishermen have created a huge impact on marine biodiversity, irrespective of marine and riverine laws that are put in place and practiced. There have been attempt to provide subsistence fishing extension officer services to facilitate in bringing subsistence fishermen fully into the management system, in an orderly and equitable manner, by facilitating the granting of formal subsistence fishing right, providing permits via policy management and effective rules via permit applications. However the follow up process as to whether these policies and rules administered is effective or not has not been measured. This investigation attempts to identify potential fishing that should be considered as suitable for subsistence fisheries in selected highly exploitable areas. Though it cannot be confirmed from previous studies that some relevant organizations are not fully taking their responsibilities, the study will further enable exploration of options and challenges associated with future management of subsistence fisheries and provide recommendations to enable proper implementation of the policies and legislations.
Environmental Sciences
M. Env. Sc. (Agriculture and Environmental Affairs)

The seasonal periodicity of hydrology, physical and chemical water quality parameters and phytoplanktonic assemblages was studied at two sites in a large tropical Australian riverine impoundment. This study, the first in the lower Fitzroy River at Rockhampton, occurred between August 1990 and November 1993. It covered extremes in riverine flow conditions including major flooding and drought.

The annual flow regime was characterized by major flows in the "wet" season (summer and autumn) and greatly reduced or no flow in the "dry" season of winter, spring and sometimes early summer. Consequently, the thermal regime at both of the study sites was divided into two phases. The first was a phase of water column heating in the late winter to early summer. Features of this heating phase were long term stratification with progressive epilimnetic deepening, high pH, regular occurrence of epilimnetic oxygen supersaturation and decreased or undetectable levels of oxidized nitrogen in the surface layer. Hypolimnetic anoxia was recorded late in this phase. The second, between substantial wet season inflows and late winter was characterized by nutrient rich inflows and water column cooling and mixing.

Distinct interannual differences occurred in the volume, source and timing of inflows and subsequent water chemistry. In 1991, conductivity, water clarity, filterable reactive phosphorus (FRP) and pH increased markedly following major flooding from northern tributaries, while oxidized nitrogen decreased. This was in marked contrast to the drier years of 1992 and 1993 where turbidity and oxidized nitrogen were higher during the initial post-flood period and conductivity and FRP were lower. Extremes of mostly abiogenic turbidity (range 1.6 to 159 NTU) were a feature of the light climate. Ratios of euphotic depth/mixing depth below 0.3 occurred in early 1992 and 1993.

Steep gradients in the physical and chemical environment were paralleled by variations in the phytoplankton. Algal biomass (as chlorophyll a) at Site 1, midstream opposite the water intake for the city of Rockhampton, ranged from 1.5 to 56.6 ug L-1. The vertical water column distribution of chlorophyll was variable with assemblages normally dominated by phytoflagellates and various species of cyanoprokaryotes. There was also higher relative abundance of chlorophyll a (reflecting increasing dominance of cyanoprokaryotes) in the latter half of the year and at the lower end of light availability. The specific vertical water column positioning with respect to light and temperature is shown for assemblages dominated by the genera Anabaena, Aphanizomenon and Cylindrospermopsis.

The most striking aspect of the phytoplankton was the long term dominance of cyanoprokaryotes and the species richness (particularly that of cyanoprokaryotes) when compared with the dearth of information to date on other tropical rivers. Seasonal successions were varied. Regularly occurring assemblages were cyanoprokaryotes (Oscillatoriales), euglenophytes or non-flagellated chlorophytes during flows followed by flagellated chlorophytes and then cyanoprokaryotes (Nostocales) during the dry season. Genera present indicated highly eutrophic conditions. Hierarchical agglomerative clustering of phytoplankton data and comparison with a principal components analysis of corresponding environmental data were used to demonstrate the linkage between steep environmental gradients and variation in the phytoplankton assemblage. The specific environmental conditions associated with the success of various species were also analysed and presented. Using the above information, a two-part model was proposed which predicts the most likely genera of phytoplankton with respect to multidimensional environmental gradients. This model covers a wide gamut of conditions varying from highly variable lotic to lentic environments.

As Cylindrospermopsis raciborskii was considered a most important species in relation to the quality of the water supply for Rockhampton, the physical, chemical and biotic conditions prior to and during a bloom of this species are described. A number of possible grazers of C. raciborskii were identified with a view to future biomanipulation. One of these, the large ciliate, Paramecium cf. caudatum was found to be an effective grazer of toxic straight C. raciborskii in the laboratory.

This study is unique in that it analyses the impact of episodic events (eg. major flooding) on the subsequent phytoplankton in the lower Fitzroy River. The model relating phytoplankton to multidimensional environmental gradients provides great information for use in management, particularly in relation to the prediction of toxic algal blooms.