Dissertations / Theses on the topic 'Trophic flow'

Doutoramento em Biologia
Silver nanoparticles (AgNP) have been produced and applied in a variety of products ranging from personal care products to food package containers, clothing and medicine utilities. The antimicrobial function of AgNP makes it very useful to be applied for such purposes. Silver (Ag) is a non-essential metal for organisms, and it has been historically present in the environment at low concentrations. Those concentrations of silver increased in the last century due to the use of Ag in the photographic industry and lately are expected to increase due to the use of AgNPs in consumer products. The presence of AgNP in the aquatic environment may pose a risk for aquatic species, and the effects can vary from lethal to sublethal effects. Moreover, the contact of aquatic organisms with AgNP may not cause immediately the death of individuals but it can be accumulated inside the animals and consequently transferred within the food chain. Considering this, the objective of this work was to study the transfer of silver nanoparticles in comparison to silver ions, which was used as silver nitrate, within an aquatic food chain model. To achieve this goal, this study was divided into four steps: the toxicity assessment of AgNP and AgNO3 to aquatic test-species, the bioaccumulation assessment of AgNP and AgNO3 by Pseudokirchneriella subcapitata and Daphnia magna under different exposure scenarios, and finally the evaluation of the trophic transfer of Ag through an experimental design that included the goldfish Carassius auratus in a model trophic chain in which all the species were exposed to the worse-case scenario. We observed that the bioconcentration of Ag by P. subcapitata is mainly driven by ionic silver, and that algae cannot internalize these AgNPs, but it does internalizes dissolved Ag. Daphnia magna was exposed to AgNP and AgNO3 through different exposure routes: water, food and both water and food. The worse-case scenario for Daphnia Ag bioaccumulation was by the joint exposure of contaminated water and food, showing that Ag body burdens were higher for AgNPs than for AgNO3. Finally, by exposing C. auratus for 10 days through contaminated water and food (supplied as D. magna), with another 7 days of depuration phase, it was concluded that the 10 days of exposure were not enough for fish to reach a plateau on Ag internal concentration, and neither the 7 days of elimination were sufficient to cause total depuration of the accumulated Ag. Moreover, a higher concentration of Ag was found in the intestine of fish when compared with other organs, and the elimination rate constant of AgNP in the intestine was very low. Although a potential for trophic transfer of AgNP cannot be suggested based in the data acquired in this study, there is still a potential environmental risk for aquatic species.
As nanopartículas de prata (AgNP) têm sido produzidas e utilizadas em uma grande variedade de bens de consumo, desde produtos de higiene pessoal a embalagens de alimento e utensílios médicos. A ação antimicrobiana das nanopartículas de prata é o principal fator que as torna úteis e ideais para tais aplicações. A prata é um metal não essencial e pode ser encontrado no ambiente em concentrações ecologicamente irrelevantes. No passado, a atividade de revelação fotográfica era a principal fonte de prata no ambiente. Ultimamente, estas concentrações têm aumentado devido à vasta utilização das nanopartículas de prata na indústria. A presença da prata no ambiente pode constituir um risco para as espécies e os efeitos causados podem ser do tipo letal ou sub-letal. Para além disso, a exposição dos organismos à prata, mesmo que não os leve à morte imediata, pode causar uma acumulação deste metal, e que poderá ser transferido entre os níveis tróficos da cadeia alimentar aquática. Tendo isto em consideração, o objetivo deste trabalho foi estudar a transferência das nanopartículas de prata numa cadeia trófica aquática modelo, e comparar os mesmos processos com a exposição a nitrato de prata (AgNO3). Para alcançar este objetivo, este trabalho foi dividido em quatro estudos: avaliação da toxicidade das AgNP e do AgNO3 para as espécies em estudo, uma posterior avaliação da bioconcentração das AgNP e do AgNO3 pela alga verde P. subcapitata, o estudo da bioacumulação da prata em Daphnia magna, exposta a diferentes vias de contaminação (água, alimento e ambos) e por último a avaliação da transferência das AgNP e de AgNO3 através de um desenho experimental que incluiu o peixe Carassius auratus expostos a água e alimento contaminados. Os resultados obtidos com estes estudos indicam que a bioacumulaçãoo da prata na alga P. subcapitata ocorre devido à internalização dos iões de prata, e não das nanopartículas. Estas aparentemente encontram-se em aglomerados próximas às células das algas, não entrando nas células/algas. Relativamente à Daphnia magna, o maior fator de bioacumulação foi obtido quando estas foram expostas à água e alimento contaminados com AgNP. Finalmente observou-se que os peixes não atingiram um equilíbrio na concentração interna de prata, e que o órgão que apresentou maior bioacumulação de prata foi o fígado. Para além disso, foi verificada no fígado uma taxa de eliminação muito baixa, o que nos pode levar a sugerir que as nanopartículas de prata podem persistir neste órgão. Apesar de não se verificar um potencial para transferência trófica, as nanopartículas de prata podem representar risco para as espécies aquáticas aqui estudadas.

Conceptual models of stream continua predict that energy flow and consumer functional structure change predictably with the physical attributes of a stream. To quantify these relationships in a prairie landscape, I estimated macroinvertebrate production, benthic organic matter standing stocks, and resource consumption and egestion by consumer groups along a longitudinal continuum of Kings Creek, a tallgrass prairie stream draining the Konza Prairie Biological Station in Eastern Kansas. I sampled benthic macroinvertebrates for 1 year from three stream reaches, each bordered by distinct riparian vegetation. Riparian vegetation along the continuum ranged from grassy headwaters to shrubby mid-reaches to lower reaches bordered by gallery forest. Total habitat-weighted production ranged from 31.9 g ash-free dry mass (AFDM) m-2 y-1 in the grassy headwater reach to 9.1 g AFDM m-2 y-1 in the shrubby reach to 17.0 g AFDM m-2 y-1 in the gallery forest. Functional group contributions to production generally were similar along the continuum, with collector-gatherers (40%-56% of total) and Predators (23%-38%) dominating all reaches. Quantitative food webs indicated detrital pathways dominated energy flow in all reaches, with collector-gatherers accounting for most energy flow through primary consumers. Predators were well represented and consumed 75% - 135% of total macroinvertebrate production whereas shredders (2-4%), scrapers (11-15%), and filterers (<1%) consumed a small percentage of their particular resources. High production and consumption estimates for macroinvertebrate predators suggest top-down controls are important in this system. Although functional structure was fairly similar among reaches, changes in energy flow through some groups reflected longitudinal changes in resource availability. Results indicate that this tallgrass prairie stream ecosystem is intermediate in the context of predictions of conceptual stream continua models, and biotic interactions may override some predicted responses to changes in the physical template.

Doutoramento em Biologia
Cadmium is considered one of the most toxic metals to aquatic organisms. This naturally occurring metal is found in the environment in low concentrations due to natural processes, such as volcanic eruptions, natural crust erosion and also anthropogenic activities, such as mining and smelting. As a by-product of zinc mining, cadmium can reach aquatic environment through leaching or to rainwater runoff from the mine areas. It is a non-essential metal for organisms that even at relatively low concentrations can be toxic and may cause adverse effects due to its high bioaccumulation tendency. Considering this, the objective of this work was to study the toxicity and bioaccumulation potential of cadmium within different model marine trophic levels. To achieve this goal, this work was divided into four studies: i) assess the eco- and genotoxicity of cadmium to three marine test-species, representing different marine trophic levels, ii) determine the bioconcentration potential of cadmium in the calanoid copepod Acartia tonsa under different environmental conditions, such as pH, salinity and temperature, iii) evaluate the uptake and depuration kinetics of cadmium by the estuarine ditch shrimp Palaemon varians considering three different uptake routes: water, diet, water + diet and iv) assess the bioaccumulation patterns of cadmium in the Senegalese sole Solea senegalensis, a final consumer, and the possible risk and implications the consumption of the edible fraction of both shrimps and fish may bear to human health upon Cd exposure. We observed that the toxicity of cadmium is highly influenced by its speciation. Highest sensitivity to cadmium was observed by A. tonsa while the most sensitive endpoint was the Larval Development Ratio (LDR). Cadmium induced DNA damage to all species with increasing concentrations. The bioconcentration of cadmium by A. tonsa is strongly affected by different environmental conditions due to biological processes. The simultaneous exposure of P. varians to cadmium-contaminated water + diet showed that cadmium internal concentration was higher when compared to the individual pathways. Finally, by exposing S. senegalensis for 14 days through contaminated water and diet (supplied as Hediste diversicolor), with another 14 days of depuration phase, it was concluded that the 14 days of exposure were not enough for the fish to reach a steady state on cadmium internal concentration, and neither the 14 days of elimination were sufficient to cause total depuration of the accumulated cadmium in any of the organs. Moreover, a higher concentration of cadmium was found in the intestine of the fish when compared with the rest of the organs, and the elimination rate constant of cadmium in the liver was nule. The Target Hazard Quotient (THQ) and the Estimated Weekly Intake (EWI) values for cadmium for the edible fraction of S. senegalensis were below the acceptable levels set by the European Regulation while for the shrimps both THQ and EWI exceeded the acceptable levels established
O cádmio é considerado um dos metais mais tóxicos para organismos aquáticos, podendo ocorrer naturalmente no ambiente em concentrações muito baixas, devido a processos naturais (e.g., erupções vulcânicas, erosão da crosta natural) mas também devido a atividades antropogénicas, como a atividade mineira. Como um subproduto da exploração mineira de zinco, o cádmio pode ser libertado para o ambiente aquático através de lixiviação ou escorrências. O cádmio é um metal não essencial para os organismos mas, mesmo em concentrações relativamente baixas, pode ser tóxico, provocando efeitos adversos devido à sua elevada tendência para bioacumular. Neste contexto, o objetivo deste trabalho foi estudar a transferência de cádmio em diferentes modelos de níveis tróficos marinhos. O estudo foi dividido em quatro etapas: i) avaliar a eco- e genotoxicidade de cádmio em três espécies marinhas, representando diferentes níveis tróficos marinhos ii) determinar a bioconcentração de cádmio por Acartia tonsa sob diferentes condições ambientais, tais como pH, salinidade e temperatura, iii) a avaliação de toxicocinética de cádmio pelo camarão estuarino Palaemon varians sob três vias de exposição diferentes: água, alimentação e água + alimentação, e iv) avaliar os padrões de bioacumulação de cádmio no linguado Solea senegalensis como consumidor final, e os possíveis riscos e implicações do consumo da fração edível de camarões e peixe que pode ter para a saúde humana, após a exposição a cádmio. Foi observado que a toxicidade de cádmio é influenciada pela sua especiação. A maior sensibilidade ao cádmio foi observada em A. tonsa tendo como parâmetro mas sensível o Índice de Desenvolvimento Larvar (LDR). O cádmio induziu danos no ADN de todas as espécies utilizadas. A bioconcentração de cádmio por A. tonsa é fortemente afetada por diferentes condições ambientais devido a processos biológicos. P. varians foi exposto a cádmio através de diferentes vias de exposição: água ou alimento ou água e alimento. A exposição simultânea de P. varians a água e alimento contaminado com cádmio mostrou que a concentração interna de cádmio foi maior quando comparada com as outras duas vias de exposição. Finalmente, mesmo uma exposição através de água e alimento contaminado (fornecido como Hediste diversicolor) não foi suficiente para que o peixe S. senegalensis atingisse um plateau na concentração interna de cádmio, sendo os 14 dias de depuração insuficientes para que os organismos depurassem totalmente a concentração interna que havia sido acumulada. Adicionalmente, foi encontrada uma maior concentração de cádmio no intestino de S. senegalensis quando comparada com os outros órgãos, e a constante de eliminação de cádmio no fígado foi inexistente. Os valores do Coeficiente de Perigo Alvo (THQ) e o Consumo Semanal Estimado (EWI) para o cádmio estavam abaixo dos níveis aceitáveis estabelecidos em regulamentos europeus para a fração edível de S. senegalensis, enquanto que para P. varians tanto o THQ quanto o EWI excederam os níveis aceitáveis estabelecidos.

Les changements d'intensité dans l'utilisation des sols et la dégradation de l'environnement en raison de activités humaines ont entraîné une forte altération des écosystèmes tropicaux, en particulier dans les cours d'eau de tête de bassin de la savane néotropicale. Les pressions humaines liées à l'expansion agricole et à l'urbanisation ont conduit à une réduction drastique de la couverture végétale indigène, affectant les zones riveraines et altérant le fonctionnement des écosystèmes aquatiques. Il est urgent de quantifier et de prévoir comment les communautés aquatiques répondent aux changements de l'utilisation des sols pour guider les efforts de conservation et de gestion des ressources naturelles. Dans ce contexte, cette thèse visait à évaluer à quelles échelles spatiales la relation entre habitat et communautés de macroinvertébrés benthiques s'exprimait le plus fortement et comment l'intensité d'utilisation des sols affectait les relations trophiques et la composition en traits biologiques des communautés de macroinvertébrés benthiques. Dans le chapitre 1, j'évalue comment l'intensité d'utilisation des sols (représentée par un gradient depuis la végétation autochtone, au pâturage, et à la plantation de canne à sucre et la végétation indigène) influe sur les flux d'énergie et les niches trophiques des macroinvertébrés benthiques. Ensuite, j'ai évalué à quelle échelle spatiale (bassin versant, localité) et pour quelles variables, le lien entre la composition taxonomique et fonctionnelle des assemblages de macroinvertébrés benthiques était le mieux exprimé (chapitre 2). Enfin, j'ai montré que les perturbations anthropiques avait unj impact sur la diversité fonctionnelle des assemblages de macroinvertébrés benthiques (chapitre 3). Les résultats présentés ici montrent que les changements d'intensité de l'utilisation des sols conduisent les assemblages de macroinvertébrés benthiques vers des comportements d'alimentation plus généralistes avec un chevauchement des niches trophiques (chapitre 1). De plus, les variables environnementales à l'échelle locale et du bassin versant expliquent de façon significative les variations de la composition taxonomique et fonctionnelle des assemblages d'Ephéméroptères, Plécoptères et Trichoptères, mais les variables décrivant l'intensité d'utilisation des sols expliquent le mieux les différences de composition fonctionnelle entre les différents sites (chapitre 2). Enfin, J'ai montré que les sites quasi-naturels (dans des conditions de référence) ont des assemblages de macroinvertébrés plus spécialisés comparés aux sites perturbés (chapitre 3). Les résultats corroborent le fait que la biodiversité doit être évaluée en tenant compte de variables agissant à de multiples échelles spatiales et que les éléments fonctionnels des communautés biologiques doivent être considérés, en vue de la conservation et du développement d'outils prédictifs. Cette étude contribue à une meilleure compréhension de la structure et du fonctionnement des cours d'eau dans la savane néotropicale dans le contexte du développement d'outils d'évaluation environnementale. Ces approches contribueront à l'élaboration de mesures de gestion et de conservation plus appropriées et permettront d'examiner les conséquences futures d'une poursuite de la dégradation des conditions écologiques dans les cours d'eau tropicaux
Changes in land cover and use and the associated environmental degradation due to human activities have resulted in extreme alterations of tropical ecosystems, especially in headwater streams and their watersheds in the neotropical savanna. Human pressures related to agricultural expansion and urbanization have led to drastic reductions in native vegetation cover, affecting riparian zones and degrading aquatic ecosystem functioning. There is an urgent need to quantify and predict how aquatic communities respond to different intensities of land use to guide conservation and natural resource management efforts. This thesis aims to evaluate how spatial scales influence the relationship between habitat and benthic macroinvertebrate communities and how land use intensity affects the trophic relationships and biological traits of macroinvertebrates. In Chapter 1, we evaluated how the intensity of land use (represented by a gradient moving from native vegetation toward pasture and sugar cane plantations) influences the energy flow and trophic niches of macroinvertebrates. In Chapter 2, we investigated the spatial scales (e.g., catchment, local) that most influence the taxonomic and functional composition of macroinvertebrate assemblages. Finally, in Chapter 3, we examined the impacts of human pressures on the functional diversity of macroinvertebrate assemblages. we showed that the intensity of land use affects benthic macroinvertebrate assemblages, yielding more generalist feeding behaviors with greater overlap of trophic niches (Chapter 1). In addition, environmental variables at the local and catchment scales significantly explained the variations in the taxonomic and functional composition of Ephemeroptera, Plecoptera and Trichoptera assemblages, but land use variables best explained the differences in functional composition among sites (Chapter 2). Finally, we showed that less impacted sites (under reference conditions) had more specialized and more functional diverse macroinvertebrate assemblages compared to disturbed sites (Chapter 3). These results corroborate the idea that biodiversity should be evaluated at multiple spatial scales and that the functional elements of biological communities should be considered when aiming for conservation and the development of predictive tools. This study contributes to a better understanding of the structure and functioning of streams in the neotropical savanna by subsidizing the development of environmental assessment tools. Such approaches will contribute to the development of more appropriate management and conservation measures that will allow for evaluation of the impacts on biota of further degradation of the ecological conditions in tropical streams

This study is part of a project that was conducted by Florida International University (FIU), which designed, built, and characterized a constructed wetland (CW) wastewater treatment system in El Salvador, Central America. This study focuses on the detailed performance of a field-scale CW in the tropics, consisting of a subsurface flow wetland (SSF) and a surface flow wetland (SF). The SSF had a total area of 151.2 sq. m., filled with gravel and planted with Phragmites, Thalia, and Brachiaria, along three independent cells operating with a flow in parallel and receiving the influent domestic wastewater from a facultative lagoon and preceded the SF. The SF was a shallow open basin containing alternating regions of open water (195 sq. m. total) with submerged aquatic plants (Elodea) and regions of shallower water (605 sq. m. total) filled with emergent wetland vegetation (Typha, Thalia, and Cyperus). The design, construction, startup and operation phases of the field scale CW in that tropical setting are thus described with detail, including both SSF and SF characterization of influent and effluents. The SSF average hydraulic detention times during the wet and dry season were 2 days ± 0.9 days and 4 days ± 0.4 days, respectively; and the SF average hydraulic detention times during the wet and dry season were 20 days ± 11.1 days and 77 days ± 19.5 days, respectively. Brachiaria/Cyperus presented better results during the wet season with average BOD5 residuals of 36% ± 25%, and Thalia/Thalia during the dry season with average BOD5 residuals of 33% ± 22%. Phragmites/Typha presented better results during both seasons with average TSS residuals of 2% ± 3% (wet season), and 2% ± 2% (dry season). Residuals are also presented for COD, Oil & Grease, Total Fecal Coliform, Total Phosphorus, and Total Nitrogen. In addition, an assessment of the empirical models used in the design of the system is completed, having the EPA methodology as the preferred for BOD5 removal and three methodologies for TSS removal under tropical climate conditions. A comparison of the differences in treatment associated with each one of the selected plants and their combinations is also discussed. In summary, results strongly suggest that the CW system can effectively reduce contaminants in wastewater to levels that are comparable with the objective levels (i.e., secondary treatment levels).

While empirical examples have demonstrated the openness of ecosystems to resource flows, we still have a limited ability to make general predictions about the magnitude of, or controls on, the effects of subsidies. I studied the impacts of spatial resource subsidies, and the controls on those effects, using several different consumer species in stream and riparian habitats. I quantified the variation in effect size between habitats, recipient consumers, trophic level of the consumer, and productivity of recipient and donor habitats and tested the magnitude of the effect of a subsidy in a system where theory predicted small magnitude or little impact based on productivity contrasts. I tested the consequences of subsidies on the individual fitness of a riparian spider when delivery of a subsidy is variable in time. I demonstrated that the quantity of a subsidy arriving in a recipient habitat may be altered by consumers (waterstriders) feeding at the interface between habitats and that this control varies with habitat type. Overall, three key themes emerge: 1) the identity of consumers and habitats matters, subsidies do not act the same way in all circumstances, 2) the quantity and timing of a subsidy can interact with the specific ecological requirements or life history o f an organism such that a subsidy received at the wrong time in an organism's development may actually have negative consequences for relative adult fitness, and 3) the species composition of both boundaries and recipient habitats may alter the consequences of subsidies. This thesis supports the developing consensus that understanding the factors that determine the response of consumers in a recipient community to a resource subsidy is essential to the development of landscape level approaches to open systems.
Forestry, Faculty of
Graduate

Large areas in the humid tropics are currently undergoing land-use change. The decrease of tropical rainforest, which is felled for land clearing and timber production, is countered by increasing areas of tree plantations and secondary forests. These changes are known to affect the regional water cycle as a result of plant-specific water demand and by influencing key soil properties which determine hydrological flow paths. One of these key properties sensitive to land-use change is the saturated hydraulic conductivity (Ks) as it governs vertical percolation of water within the soil profile. Low values of Ks in a certain soil depth can form an impeding layer and lead to perched water tables and the development of predominantly lateral flow paths such as overland flow. These processes can induce nutrient redistribution, erosion and soil degradation and thus affect ecosystem services and human livelihoods. Due to its sensitivity to land-use change, Ks is commonly used to assess the associated changes in hydrological flow paths. The objective of this dissertation was to assess the effect of land-use change on hydrological flow paths by analysing Ks as indicator variable. Sources of Ks variability, their implications for Ks monitoring and the relationship between Ks and near-surface hydrological flow paths in the context of land-use change were studied. The research area was located in central Panama, a country widely experiencing the abovementioned changes in land use. Ks is dependent on both static, soil-inherent properties such as particle size and clay mineralogy and dynamic, land use-dependent properties such as organic carbon content. By conducting a pair of studies with one of these influences held constant in each, the importance of static and dynamic properties for Ks was assessed. Applying a space-for-time approach to sample Ks under secondary forests of different age classes on comparable soils, a recovery of Ks from the former pasture use was shown to require more than eight years. The process was limited to the 0−6 cm sampling depth and showed large variability among replicates. A wavelet analysis of a Ks transect crossing different soil map units under comparable land cover, old-growth tropical rainforest, showed large small-scale variability, which was attributed to biotic influences, as well as a possible but non-conclusive influence of soil types. The two results highlight the importance of dynamic, land use-dependent influences on Ks. Monitoring studies can help to quantify land use-induced change of Ks, but there is a variety of sampling designs which differ in efficiency of estimating mean Ks. A comparative study of four designs and their suitability for Ks monitoring is used to give recommendations about designing a Ks monitoring scheme. Quantifying changes in spatial means of Ks for small catchments with a rotational stratified sampling design did not prove to be more efficient than Simple Random Sampling. The lack of large-scale spatial structure prevented benefits of stratification, and large small-scale variability resulting from local biotic processes and artificial effects of destructive sampling caused a lack of temporal consistency in the re-sampling of locations, which is part of the rotational design. The relationship between Ks and near-surface hydrological flow paths is of critical importance when assessing the consequences of land-use change in the humid tropics. The last part of this dissertation aimed at disclosing spatial relationships between Ks and overland flow as influenced by different land cover types. The effects of Ks on overland-flow generation were spatially variable, different between planar plots and incised flowlines and strongly influenced by land-cover characteristics. A simple comparison of Ks values and rainfall intensities was insufficient to describe the observed pattern of overland flow. Likewise, event flow in the stream was apparently not directly related to overland flow response patterns within the catchments. The study emphasises the importance of combining pedological, hydrological, meteorological and botanical measurements to comprehensively understand the land use-driven change in hydrological flow paths. In summary, Ks proved to be a suitable parameter for assessing the influence of land-use change on soils and hydrological processes. The results illustrated the importance of land cover and spatial variability of Ks for decisions on sampling designs and for interpreting overland-flow generation. As relationships between Ks and overland flow were shown to be complex and dependent on land cover, an interdisciplinary approach is required to comprehensively understand the effects of land-use change on soils and near-surface hydrological flow paths in the humid tropics.
Tropische Regionen sind einem andauernden Landnutzungswandel unterworfen. Einerseits wird tropischer Regenwald für Holz- und Flächengewinnung abgeholzt, andererseits fallen Flächen im Zuge der Urbanisierung brach. Diese werden zum Teil mit Nutzholz-Plantagen aufgeforstet, zum Teil entwickelt sich auf ihnen natürlicher Sekundärwald. Änderungen in der Landnutzung beeinflussen Bodeneigenschaften und dadurch implizit den Wasserkreislauf der Region. Eine dieser wichtigen landnutzungsabhängigen Bodeneigenschaften ist die gesättigte hydraulische Leitfähigkeit oder Permeabilität, die maßgeblich die Versickerungsrate im Boden bestimmt. Eine niedrige Permeabilität hemmt die (vertikale) Versickerung und kann dazu führen, dass laterale hydrologische Fließpfade wie z.B. Oberflächenabfluss aktiviert werden. Dadurch wird sowohl die Bodenerosion und Nährstoffverlagerung verstärkt als auch die Auffüllung des Grundwasserspeichers verringert. In welchem Maße jedoch die Änderung der Permeabilität während des Landnutzungswandels eine Änderung der hydrologischen Fließpfade nach sich zieht, ist noch unzureichend erforscht. Die Zielstellung der vorliegenden Dissertation war, mit Hilfe der Permeabilität als Indikatorvariable die Auswirkungen des Landnutzungswandels auf bodennahe hydrologische Fließpfade zu beurteilen. Dabei sollten die Quellen der Variabilität der Permeabilität anhand des Einflusses von Bodentyp und Landnutzung eingeschätzt, diese Variabilität in das Design einer Probenahmestrategie für die Permeabilität integriert und die Auswirkungen dieser Einflüsse auf die Aktivierung lateraler Fließpfade untersucht werden. Die Studien wurden in Panama durchgeführt, da dieses Land stark vom Landnutzungswandel betroffen ist, eine gute Forschungsinfrastruktur aufweist und sich durch die hohen Niederschläge des tropischen Klimas Änderungen im Wasserkreislauf besonders stark auswirken. Zwei Teilstudien zu den Quellen der Variabilität der Permeabilität lieferten Hinweise auf einen möglichen Einfluss des Bodentyps, der jedoch durch den lokal stärkeren Einfluss der Landnutzung überprägt wurde. Auf regionaler Skala wurde die Erholung der Permeabilität unter Sekundärwald nach einer vorhergehenden Weidenutzung belegt. Beide Studien deuteten auf einen maßgeblichen Einfluss der Landnutzung und der räumlichen Struktur der Permeabilität auf die untersuchten Prozesse hin. Für die effiziente Abschätzung zeitlicher Veränderungen der Permeabilität, wie sie im Zuge des Landnutzungswandels auftritt, ist die Einbeziehung dieser räumlichen Strukturen in das Design einer Probenahmestrategie für die Permeabilität von großer Bedeutung, wie in einem Vergleich vier verschiedener Designs gezeigt wurde. Der Zusammenhang zwischen der Permeabilität und der Entstehung von Oberflächenabfluss konnte nicht durch einfache Ansätze, wie dem Vergleich der Permeabilität mit Regenintensitäten oder der Betrachtung des Gebietsabflusses, erklärt werden. Vielmehr scheint ein komplexes Zusammenspiel aus meteorologischen, biologischen, bodenkundlichen und hydrologischen Faktoren zu wirken. So wurde die räumliche Struktur des Oberflächenabflusses im Untersuchungsgebiet vermutlich durch eine Kombination aus Landnutzungs- und Permeabilitäts-Einflüssen bedingt, zu deren Aufklärung weitere notwendige Messungen vorgeschlagen werden. Zusammengefasst konnte anhand der Permeabilität der Einfluss des Landnutzungswandels auf die hydrologischen Fließpfade gut aufgezeigt werden. Eine besondere Bedeutung kommt hierbei der Betrachtung der landnutzungsabhängigen räumlichen Struktur der Permeabilität zu. Für die Prozessaufklärung der Aktivierung lateraler Fließpfade müssen jedoch Messungen aus verschiedenen Disziplinen kombiniert werden.

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Universidade Federal de Sao Carlos
The objective of this study was to analyze the structure, composition, trophic ecology and food items shared by the fish fauna in the stream Beija -Flor, located in Jataí Ecological Station ( 21 ⁰ 36'32 .8 " S 47 ⁰ 48'0 .54 " W ), besides characterizing the trophic ecology of the species Hemigrammus marginatus, one of the most abundant in the Beija-Flor stream. The samples of fish were collected monthly from August 2011 to July 2012, using gill nets, trawl nets and baited traps in five sampling stations distributed along the Beija-Flor stream. The fish were fixed in 10% formalin in the field and in the laboratory were identified and subjected to biometric measurements. The stomachs were weighed and transferred to 70% alcohol and stomach contents were examined under a stereomicroscope to the lowest possible taxonomic level. Forty four fish species belonging to 33 genera, 16 families and 5 orders were collected. Most species were accidental ( 43.18 % ), followed by constant species ( 38.64 % ) and accessory (18.18 % ). The diet of 30 species was analyzed. The main dietary habit was insectivorous, followed by omnivorous habits, herbivorous, piscivorous and detritivore. The dietary overlap was high in several species during periods of dry and flood. Hemigrammus marginatus was classified as an insectivore. Food items of autochthonous origin of the orders Ephemeroptera and Trichoptera were more important during the dry season, while the items of allochthonous origin of the order Hymenoptera, were more important in the rainy season. The increase in the quantity and variety of food items during the flooding causes some species of fish to become more generalist and share food resources. Hemigrammus marginatus, Astyanax altiparanae, Metynnis maculatus, Serrapinnus notomelas and Oligosarcus pintoi, have complex of interactions with the food items and can be considered key species for stream Beija- Flor. The results showed that the stream Beija-Flor is a preserved, with high species diversity by being located within the Jataí Ecological Station, but is highly threatened by being surrounded by sugar cane plantations.
O Córrego Beija-Flor, localizado na Estação Ecológica de Jataí (21⁰36 32.8 S 47⁰48 0.54 W), é formado pelos córregos da Bandeira, do Jordão e das Cabaças, e deságua no rio Mogi-Guaçu, bacia do alto Paraná. O objetivo deste trabalho foi analisar a estrutura, a composição, a ecologia trófica, e o compartilhamento de itens alimentares pela ictiofauna e caracterizar a ecologia trófica da espécie Hemigrammus marginatus, uma das espécies mais abundantes do córrego Beija-Flor. As coletas de peixes foram realizadas mensalmente no período de agosto de 2011 a julho de 2012, utilizando-se redes de espera, rede de arrasto e armadilhas iscadas do tipo covo, em cinco estações de coleta distribuídas ao longo do córrego Beija-Flor. Os peixes foram fixados em formol 10% no campo e em laboratório foram identificados e submetidos a medidas biométricas. Os estômagos foram pesados e transferidos para álcool 70% e o conteúdo estomacal foi analisado em estereomicroscópio até o menor nível taxonômico possível. Foram coletadas 44 espécies de peixes pertencentes a 33 gêneros, 16 famílias e 5 ordens. A maioria das espécies foi de ocorrência acidental (43,18 %), seguida pelas espécies constantes (38,64 %) e acessórias (18,18 %). A dieta de 30 espécies foi analisada. O principal hábito alimentar foi insetívoro, seguido pelos hábitos onívoro, herbívoro, piscívoro e detritívoro. A sobreposição alimentar foi alta em diversas espécies nos períodos de seca e cheia. Hemigrammus marginatus foi considerado insetívoro. Os itens alimentares de origem autóctone das ordens Ephemeroptera e Trichoptera foram mais importantes no período de seca, enquanto os itens de origem alóctone, da ordem Hymenoptera, tiveram maior importância no período de cheia. O aumento na quantidade e variedade de itens alimentares no período de cheia faz com que algumas espécies de peixes se tornem mais generalistas e partilhem os recursos alimentares. Hemigrammus marginatus, Astyanax altiparanae, Metynnis maculatus, Serrapinnus notomelas e Oligosarcus pintoi, possuem um complexo de interações com os itens alimentares e podem ser consideradas espécies chaves para o córrego Beija- Flor. Os resultados mostraram que o córrego Beija-Flor é um riacho preservado, com alta diversidade de espécies por estar localizado dentro da Estação Ecológica de Jataí, mas encontra-se fortemente ameaçado por estar cercado por plantações de cana de açúcar.

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems, while intensive exploitation of commercial marine species has already caused large-scale reorganizations of biological communities in many of the world’s marine ecosystems. Whilst our understanding on the impact of warming and acidification in isolation on individual species has steadily increased, we still know little on the combined effect of these two global stressors on marine food webs, especially under realistic experimental settings or real-world systems. We particularly lack evidence of how the top of the food web (piscivores and apex predators) will respond to future climate change (ocean warming and acidification) because responses of ecological communities could vary with increasing trophic level. The picture is further complicated by the interaction of global and local stressors that affect our oceans, such as fishing pressure. Accurate predictions of the potential effects of these global and local stressors at ecosystem-levels require a comprehensive understanding of how entire communities of species respond to climate change. Mechanistic insights revealed by a combination of different approaches such as experimental manipulation of food webs, and integrated with ecosystem modelling approaches provide a way forward to improve our understanding of the functioning of future food webs. In this thesis, I show how the combined effect of such global and local stressors could affect a three trophic level temperate marine mesocosm food web and how these outcomes could be translated to predict the response of ecological communities in a four trophic level natural food web. Using a sophisticated mesocosm experiment (elevated pCO2 of approximately 900 ppm and warming of +2.8°C), I first modelled how energy fluxes are likely to change in marine food webs in response to future climate. I experimentally show that the combined stress of acidification and warming could reduce energy flows from the first trophic level (primary producers and detritus) to the second (herbivores) and from the second to the third trophic level (carnivores). Although warming and acidification jointly boosted primary producer biomass, most of it was constrained to the base of the food web as consumers were unable to transfer unpalatable cyanobacterial production up the food web. In contrast, ocean acidification affected the food web positively by increasing the biomass from producers to carnivores. I then developed a unique approach that combines the empirical data on species response to climate change from our mesocosms experiments with historical population data (fisheries biomass and catch data) to predict future changes in a natural food web. I incorporated physiological and behavioural responses (complex species-interactions) of species from primary producers to top predators such as sharks within a time-dynamic integrated ecosystem modelling approach (Ecosim). I show that under continuation of the present-day fishing regime, warming and ocean acidification will benefit most of the higher trophic level community groups (e.g. mammals, birds, demersal finfish). The positive effects of warming and acidification in isolation will likely be reduced under their combined effect (antagonistic interaction) which is likely to be further negated under increased fishing pressure, decreasing the individual biomass of consumers. The total future fisheries biomass, however, will likely still remain high compared to the present-day scenario. This is because unharvested species in present day fishery will likely benefit from decreased competition and an increase in biomass. Nevertheless, ecological indicator such as the Shannon diversity index suggests a trade-off between biomass gain and loss of functional diversity within food webs. The mechanisms behind the increase in biomass at higher trophic level consumers and a decrease in the biomass of lower trophic levels is mostly driven by the increasing top down control by consumers on their prey through increasing trophic interaction strength and a positive response of some of the prey groups under warming irrespective of acidification. I show that in a future food web, temperature-driven changes in direct trophic interactions strength (feeding and competition) will largely determine the direction of biomass change (increase or decrease) of consumers due to higher mean interaction strength (magnitude of change). In contrast, although acidification induces a relatively small increase in trophic interaction strength it shows a much larger change in the percent interactions altered for indirect interactions. Hence, ocean acidification is likely to propagate boosted primary consumer biomass to higher trophic levels. The findings of this thesis reveal that warming in combination with acidification can increase trophic interaction strengths (top down control), resulting in a reorganization of community biomass structure by reducing or increasing the biomass of resources and consumers and a loss of functional diversity within the food web. Also, the degree to which warming and acidification will be beneficial or detrimental to functional groups in future food webs will largely depend on how interaction strengths affects individual consumers or resource groups due to multi-trophic species interaction, the availability of prey resources and the complexity of the food web considered (e.g. three or four trophic level and more diverse ecological communities).
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2018

Spatial dynamics of surface chlorophyll concentrations, diatom abundance and carbon and nitrogen stable isotope signatures of surface suspended particulate matter (SPM) were investigated during a bloom event observed in March 2003 in the vicinity of the sub-Antarctic Prince Edward Islands. The surface water composition was studied to estimate the overall importance and spatial extent of kelp derived SPM in the water column of the islands. It was observed that high chlorophyll concentrations (up to 2 mg m–3) between and downstream of the islands could not be explained by the development of the diatom bloom. Instead, microscopic and stable isotope analyses suggested that the chlorophyll signal was largely derived from the residual chlorophyll in fresh and decaying particles of small fragments of the kelp Macrocystis laevis, an endemic kelp species abundant along the shoreline of the islands. The findings of this study suggest that the dietary subsidy of kelp-derived carbon and nitrogen to benthic communities and possibly the plankton is not limited to the vicinity of kelp beds, but rather is a widespread phenomenon between the islands. Due to the dominating unidirectional Antarctic Circumpolar Current, large quantities of kelp-derived SPM may be transported and utilised tens of kilometres downstream of the islands.

Bythotrephes longimanus is an invasive, macroinvertebrate from Eurasia that was introduced into the Great Lakes region in the mid 1980s. Bythotrephes introductions into lake ecosystems have resulted in substantial changes in zooplankton communities, including declines in species richness, abundance, biomass and production. Changes in zooplankton communities may alter the quantity and quality of prey to other predators such as cisco (Coregonus artedii), a pelagic forage fish. Here, I conduct a current day comparison of cisco populations to determine if prey consumption by cisco differs in the presence of Bythotrephes, and whether changes in diet result in energetic consequences (changes in growth and condition) for cisco. Effects of Bythotrephes on native zooplankton communities have resulted in substantial changes in the variety and proportion biomass of zooplankton and macroinvertebrate prey types in cisco stomachs, which have in turn modified growth of cisco. Cisco taken from invaded lakes achieve greater total lengths but changes in condition were not detected. This effect may be driven by improved growth in the second and subsequent growing seasons, suggesting that growth consequences for young fish (that do not feed on Bythotrephes) are different than for older individuals. Length-at-structure age data indicate that by the end of the first growing season (age 1) cisco achieve comparable total body lengths in invaded and reference lakes, suggesting that food consumption by young cisco remains unchanged by Bythotrephes. Alternatively, young cisco forage may be reduced in the presence of Bythotrephes, resulting in decreased survival and similar growth among individuals that survive to age 1. In contrast, despite changes in the zooplankton community; growth of older fish (≥ age 2) was enhanced in lakes that have Bythotrephes. Improved growth among older cisco (≥ age 2) in invaded lakes may be related to the presence of a newly attainable, high energy prey source (Bythotrephes). Alternatively, enhanced growth may be explained by lower competition due to reduced recruitment of young cisco (≤ age 1) in invaded lakes. Increased knowledge regarding the effects of Bythotrephes on growth of cisco is important in furthering our understanding of its impact on lake ecosystems.
Thesis (Master, Biology) -- Queen's University, 2010-04-28 22:46:07.756