Dissertations / Theses on the topic 'Aquatic ecosystem'

Benthic algae a re one of the most important primary producers i n lotic ecosystems, and changes i n their community structure and function (e.g., metabolism) will influence other organisms at higher trophic levels or even the entire aquatic ecosystem through bottom-up effects. Since they are known to be sensiti ve to changes i n ambient conditions, benthic algae and especially diatoms have been widely used as i ndicators of environmental changes in aquatic ecosystems, particular ly i n E urope , through developi ng diatom-based indices. However, these indices have not been widely used i n other continents. Applications of such i ndices in Asia and Oceania first require testi ng to see whether the y can perform as reliable bioindicators across time and space, considering that aquatic systems are constantly changing in terms of their ambient environment such as water physical and chemical conditions. Nevertheless, few studies have been carried out to compare the environmental influences on benthic algal communities among different geographic regions, nor the influences at different spatial scales (e.g., catchment, reach, and habitat). F urthermore, few studies have considered how diatom indices perform compare with other commonly used bioindicators of aquatic ecosystem health.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment.
Science, Environment, Engineering and Technology
Full Text

Orientador : Profª. Ph.D Regina Tiemy Kishi
Coorientador : Prof. D.Sc. Stephan Fuchs
Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia de Recursos Hídricos e Ambiental. Defesa: Curitiba, 15/03/2016
Inclui referências : f.75-78
Resumo: Os metais traço são utilizados na indústria e na agricultura e podem estar presentes em efluentes de mineração e esgoto. Assim, esses elementos atingem o ambiente e podem ser prejudiciais aos organismos, meio ambiente e às pessoas. Um monitoramento representativo é essencial para a gestão dos recursos hídricos e consequente prevenção à poluição. Monitoramentos convencionais da água algumas vezes podem não revelar a real condição do ambiente. Isto acontece devido às condições de lançamento e chegada dos poluentes ao sistema, à tecnologia disponível para quantificar a concentração e devido às características da própria substância monitorada. No caso dos metais traço, estes têm uma atração maior por outras partículas (sólidos suspensos, solo, sedimento, carbono orgânico dissolvido), as quais sedimentam, não permanecendo na coluna d'água. Outro fator a ser considerado é que as fontes de metais traço são geralmente intermitentes e as coletas são não contínuas. Além disto, os limites de detecção são altos e não detectam tais elementos na água. Desta forma, o biofilme é uma técnica alternativa de monitoramento, pois analisa o nível de contaminação em um intervalo de tempo. Para este estudo foram construídos dois amostradores. Amostras de biofilme, água e sedimento foram coletadas ao longo de oito meses para dois pontos de monitoramento, um na bacia do rio Barigüi e outro na bacia do rio Miringuava. Parâmetros de qualidade da água, granulometria e conteúdo de metais traço foram estimados. Os resultados mostram que o biofilme identificou os metais traço em praticamente todas as campanhas, enquanto que para as amostras de água isto não aconteceu. As amostras de sedimento representaram a poluição, porém não foi possível determinar o tempo da contaminação pelo método de coleta utilizado. O biofilme representou as diferenças no uso e ocupação do solo, representando poluição consistente com cada bacia hidrográfica. Palavras-chave: biofilme, metais traço, monitoramento, rio Miringuava, rio Barigüi.
Abstract: Trace metals are used in industries and agriculture and can be present in mining and sewer effluents. In such context, these elements can enter the environment and be very harmful to organisms, environment and people. A representative monitoring is essential for water resources management and, consequently, pollution prevention. Conventional water monitoring do not always show real environment condition. That happens because of effluent release conditions, pollution arrival system conditions, available technology to identify element concentrations and monitoring substance characteristics. Specifically for trace elements, they tend to adhere to other particles (suspended matter, soil, sediment, DOC) and deposit in riverbed. Other factor is that trace metal sources are usually from intermittent discharges and collections are not continuous. Besides that, usual techniques have high quantification limit and do not identify these elements in water. Thus, biofilm is an alternative monitoring technique for trace metals evaluation since it analyses contamination level in a time space. For this study, two biofilm samplers were constructed. Biofilm, water and sediment samples were collected for an eight month period in two monitoring sites, Barigüi and Miringuava watershed. Water quality parameters, granulometry, and trace metals content were estimated. Results showed that biofilm identified metals in almost every campaign, while water samples did not. On the other hand, sediment samples represented pollution but it was not possible to determine the contamination time by the used collection method. Biofilm also represented differences in soil use and occupation, representing consistent pollution potential for each basin. Keywords: biofilm, trace metals, monitoring, Miringuava River, Barigüi River.

As a result of research carried out within the last decade to assess the diversity of macroinvertebrates of the Salt River in the Western Cape Province, South Africa, surveys of macroinvertebrates of 20 sites on 11 selected rivers from the same mountain range source were undertaken. This was done to make a preliminary assessment of the conservation status of the rivers of this region. Aquatic insects from the orders Ephemeroptera, Odonata, Plecoptera, Megaloptera, Trichoptera and the dipteran family Simuliidae were collected using techniques to maximize the number of taxa found. The insects collected were identified to species level where possible. Water physicochemical parameters were recorded at all sites for each sampling trip to characterize these rivers and to establish a set of baseline data for future comparisons. These parameters included measurements made on site and analysis of the concentrations of all the major ions in water samples in the laboratory. Multivariate analyses including Principle Components Analysis and Canonical Correspondence Analysis were used to reveal patterns within the water physicochemistry and species distributional data. Results include the identification of 123 species from 70 genera and 30 families. A total of 31 species were found to be undescribed, of which 17 were not previously collected and are thus completely new to science. In addition, four of these species could not be placed into any known genus. The analysis of water physicochemistry showed a clear distinction between rivers of Table Mountain sandstone and Bokkeveld shale origin. Downstream effects of anthropogenic influences were discernable too. Distinct macroinvertebrate assemblages were found based upon stream order and water chemistry composition. pH proved to be the most important driver of invertebrate assemblage composition. The high levels of endemism of the macroinvertebrates found within the upper reaches of these rivers and their degree of ecological specialization make these systems a priority for the conservation of aquatic biodiversity on a national and global scale.

A major challenge of ecologists is to discover general mechanisms that explain how climate shapes ecological communities and ecosystems. Efforts have traditionally focused on direct effects, but a growing body of evidence suggests that indirect effects of climate, via altering species interactions, may be more important. Predators are often particularly vulnerable to environmental stress, thus effects of climate may cascade through ecosystems by altering top-down trophic interactions. In Costa Rica, where climate change is predicted to decrease the amount of precipitation, bromeliads contain aquatic insect food-webs largely controlled by the top predator, damselfly nymphs. Community composition varies with bromeliad size. Notably, top predators occur only in large bromeliads, possibly because the probability of drought stress decreases with bromeliad size. Thus, bromeliads are ideal systems to study the relative importance of direct and indirect effects of climate on community and ecosystem responses. To determine whether climate governs community composition directly, I regressed insect drought sensitivity, which I obtained experimentally, against insect habitat size sensitivity, which I calculated from observational data. To examine the importance of indirect drought effects from altered trophic interactions, I experimentally manipulated trophic composition and drought in mesocosms mimicking a single bromeliad leaf well and measured changes in community composition, decomposition, and water quality. Climate directly governed community composition at the scale of the bromeliad, as drought sensitivity strongly predicted habitat size sensitivity. At the scale of the leaf well, drought altered community composition and ecosystem properties indirectly by reducing top-down control from the top predator. Moreover, indirect effects of drought cascaded through the food-web to affect ecosystem functioning (decomposition) and state (water quality). These findings suggest that in complex habitats, such as bromeliads, direct (physiological) effects of climate may sufficiently explain community composition. However, in isolated habitats, such as a single leaf well in which dispersal is hindered, indirect effects of climate, via altered trophic interactions, may emerge and cascade through the ecosystem. The relative importance of direct and indirect effects of climate may thus depend on habitat scale.
Science, Faculty of
Zoology, Department of
Graduate

Orientador: Gustavo Quevedo Romero
Texto em português e inglês
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Com a intensificação das transformações dos sistemas naturais pela atividade humana, o entendimento dos processos que afetam as comunidades e o funcionamento dos ecossistemas tornou-se um tema central para a ecologia contemporânea. As interações entre as espécies, bem como as interações entre as espécies e os componentes abióticos do meio ambiente, afetam tanto os padões de diversidade biológica como funções ecossistêmicas. Neste trabalho, buscou-se compreender o papel relativo das interações predador-presa e dos componentes abióticos sobre as propriedades das comunidades e funcionamento dos ecossistemas. No primeiro capítulo, investiguei o papel do tamanho do habitat sobre os efeitos de predadores terrestres na estrutura de comunidades e funcionamento de ecossistemas adjacentes. O tamanho do habitat modera cascatas tróficas dentro de ecossistemas, deste modo, esperei que efeitos similares do tamanho do habitat poderiam afetar cascatas tróficas que ocorrem através dos limites dos ecossistemas. No segundo capítulo, explorei predições relacionadas a variação no formato de pirâmides tróficas de biomassa ao longo de gradientes ambientais (tamanho do habitat, concentração de detritos e produtividade). Além disso, investiguei a contribuição relativa dos efeitos de consumo direto e do risco de predação nas interações predador-presa como mecanismos estruturadores de pirâmides tróficas de biomassa. No terceiro capítulo, tive como objetivo investigar os efeitos de dois extremos de um gradiente ambiental e os efeitos de predadores sobre os componentes da diversidade de presas detritívoras (i.e., diversidade funcional, filogenética e taxonômica). Além disso, explorei o papel relativo do ambiente, dos predadores e dos componentes da diversidade sobre o funcionamento ecossistêmico (i.e., decomposição e fluxo de nitrogênio). Os resultados encontrados nos três capítulos demonstram que fatores abióticos são cruciais na determinação das propriedades das comunidades, interações predador-presa e, consequentemente, no funcionamento ecossistêmico. O papel relativo dos efeitos cascatas de predadores é altamente dependente das condições ambientais que medeiam as interações entre predadores e presas
Abstract: In the face of the increasing transformation of environmental conditions by human activity, understanding the processes that affect communities and ecosystem functioning has become fundamental goals in ecology. The interactions between coexisting species and, their interactions with the abiotic components of environment, affect the patterns of biological diversity and functions of ecosystems. In this study, I sought to understand the relative role of predator-prey interactions and of abiotic factors on the communities¿ properties and ecosystem functioning. In the first chapter, I investigated the role of habitat size in mediating the effects of terrestrial predators on the structure of communities and the functioning of adjacent ecosystems. Habitat size mediated trophic cascades within ecosystems; therefore, I expected that similar effects of habitat size affect cross-ecosystem trophic cascades. In the second chapter, I explored predictions related to the variation of trophic pyramids of biomass across environmental gradients (i.e., habitat size, detritus concentration and productivity). Furthermore, I investigated the relative contribution of consumptive and non-consumptive effects of predators on the shape of trophic pyramids of biomass. In the third chapter, I sought to investigate the effects of two extremes of an environmental gradient and the effects of predators on the components of detritivores diversity (i.e., functional, phylogenetic and taxonomic). Moreover, I explored the relative role of environment, predators and detritivore diversity components on the functioning of ecosystems (i.e., detritus processing and nitrogen flux). The results from this study demonstrated that abiotic factors are crucial determinants of community properties, predator-prey interactions and ecosystem functioning. The relative role of the predators cascading effects are strongly dependent on the environmental conditions which mediate the interactions between predators and prey
Doutorado
Ecologia
Doutora em Ecologia

Connectivity in aquatic ecosystems is a broad concept that refers to the transfer of both abiotic (i.e. matter and energy) and biotic (organisms) elements through the landscape across a range of spatial and temporal scales. The present study focuses on the patterns of connectivity between populations of aquatic insects in headwater streams. Dispersal, emigration and immigration are the demographic forms of population connectivity, which are largely thought to be by the winged adult stages that spend much of their lives in the riparian zone. These flying adults may disperse laterally and longitudinally to circumvent terrestrial barriers between headwater streams and catchments, thus allowing gene flow between populations in different streams. Riparian vegetation has a potentially strong influence on the survival and success of adult stages through the alteration of the microclimate, habitat structure and potential food sources. Habitat fragmentation caused by forest harvesting can reduce population connectivity by increasing the area of open forest and altering microclimatic conditions, particularly air temperature and humidity. Degradation of adjacent terrestrial habitat through forest harvesting may egatively affect adult dispersal because altered microclimatic conditions may create a barrier to dispersal. For example, the extreme conditions caused by harvesting may exceed tolerance limits of adult aquatic insects. In addition, aquatic insect life history traits may influence the degree to which forest harvesting affects their populations. For example, if a species with a short emergence period emerges during peak summer temperatures, temperatures could be higher in cleared areas compared to forested, thus exceeding the tolerance limit of the species. However, little direct evidence exists on the effects of selective harvesting and the associated changes to the microclimate on adult dispersal and genetic population connectedness.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

This thesis explores the potential of the emergent macrophyte Sparganium erectum to act as a physical ecosystem engineer and delivers an understanding of the vegetative processes that enable it to function in such a capacity. An ecosystem engineer is an organism that creates or modifies habitat; the habitats in question are rivers, particularly low energy sections, the modification relates to the capacity of the species to trigger geomorphological change via a process of flow velocity reduction, sediment accumulation, and reinforcement by underground biomass. The influence of S. erectum, and other aquatic species, on flow and sediment accumulation has been demonstrated before, but its changeable influence at different energy conditions and a detailed understanding of how its morphology influences physical processes has yet to be revealed. To address these gaps in understanding, the research conducted within this thesis is divided into three distinct results chapters; Chapter 4 investigates the influence of S. erectum on patterns of flow and sediment at three reaches of the River Blackwater, Surrey, UK; Chapter 5 explores the capacity of the species to resist mimicked hydraulic stress, and the biomechanical traits that underpin its influence on physical processes; Chapter 6 measures the changing belowground architecture and biomass of the species. The research demonstrates that growth of S. erectum significantly alters river habitats and physical processes, but the nature of its influence varies substantially at the three study reaches, which are indicative of different energy conditions. The species demonstrates a number of subtle biomechanical and morphological traits that cause it to function so efficiently as an ecosystem engineer; these include its long growth cycle, high resistance to uprooting, and tendency for underground mass to occupy surficial layers of sediment. The study concludes by assessing the management implications of the results, which include the potential of the species as a restoration tool, given its ability to create a diversity of river habitats.

Wetlands exhibit high primary productivity and play a significant role in the global carbon cycle. Brackish and salt marshes co-occur in Southern California; yet, restoration designs often eliminate remnant brackish marshes, along with their ecosystem functions, without evaluation. Vegetation, soil organic matter, and carbon flux were compared between brackish and salt marsh habitats in the Huntington Beach Wetlands. Newland Brackish Marsh had more carbon aboveground in denser and taller vegetation than the other two marshes. Brookhurst Salt Marsh sediments had more organic matter than the other two marshes. CH₄ emissions were negligible at all sites, and there were no differences in CO₂ flux or aerobic and anaerobic microbial respiration among sites. Although these components of the carbon cycle were similar among sites in this project, such quantitative functional evaluations should be part of the restoration planning process.

Given the importance of freshwater ecosystems to human health and wellbeing, the resilience of aquatic communities to pollution from a variety of sources is of increasing concern. Current indices concentrate on structural measures to define stream health. These include community assemblages, in-stream water chemistry, and hydrological impairment through physical modifications. However, ecosystem services provided by freshwater communities rely on the underlying biogeochemical cycles that are a function of metabolic processes. At present, these are not routinely used in assessments of ecological status. A paired sub-catchment approach was used to study the effects of different land management practices on in-stream water chemistry, and their consequences to aquatic functional integrity in an agricultural landscape. The study provided an opportunity to assess the potential for ecosystem functional measures to complement the structural measures that are used to define impact on aquatic communities. High resolution analysis of the nutrient chemistry within two study reaches underpinned comparisons of community aerobic respiration, greenhouse gas transfer across the sediment-water interface and macro-invertebrate mediated processing of organic matter. This programme of measures identified clear differences between the study sub-catchments. It revealed that the management of animal waste, and control on the delivery of fine sediments to a watercourse, were key influences on in-stream functional integrity. The delivery of inorganic nutrients as a result of fertiliser application was also evident. However, the significance of this signal was masked by the overriding effect of high loads of organically loaded fine sediments and low flow in the Priors Farm reach.

Black carbon (BC), the incomplete combustion product from biomass and fossil fuel burning, is ubiquitously found in soils, sediments, ice, water and atmosphere. Because of its polyaromatic molecular characteristic, BC is believed to contribute significantly to the global carbon budget as a slow-cycling, refractory carbon pool. However, the mass balance between global BC generation and accumulation does not match, suggesting a removal mechanism of BC to the active carbon pool, most probable in a dissolved form. The presence of BC in waters as part of the dissolved organic matter (DOM) pool was recently confirmed via ultrahigh resolution mass spectrometry, and dissolved black carbon (DBC), a degradation product of charcoal, was found in marine and coastal environments. However, information on the loadings of DBC in freshwater environments and its global riverine flux from terrestrial systems to the oceans remained unclear. The main objectives of this study were to quantify DBC in diverse aquatic ecosystems and to determine its environmental dynamics. Surface water samples were collected from aquatic environments with a spatially significant global distribution, and DBC concentrations were determined by a chemical oxidation method coupled with HPLC detection. While it was clear that biomass burning was the main sources of BC, the translocation mechanism of BC to the dissolved phase was not well understood. Data from the regional studies and the developed global model revealed a strong positive correlation between DBC and dissolved organic carbon (DOC) dynamics, indicating a co-generation and co-translocation between soil OC and BC. In addition, a DOC-assistant DBC translocation mechanism was identified. Taking advantage of the DOC-DBC correlation model, a global riverine DBC flux to oceans on the order of 26.5 Mt C yr-1 (1 Mt = 1012 g) was determined, accounting for 10.6% of the global DOC flux. The results not only indicated that DOC was an important environmental intermediate for BC transfer and storage, but also provided an estimate of a major missing link in the global BC budget. The ever increasing DBC export caused by global warming will change the marine DOM quality and may have important consequences for carbon cycling in marine ecosystem.

In the mountains of the Gold Coast Hinterland (Queensland, Australia), Euastacus sulcatus (Decapoda: Parastacidae) is the largest aquatic invertebrate, largest member of the aquatic shredder guild, and probably plays a key role in the area’s stream ecology. The objective of this study was to investigate the ecological effects of E. sulcatus in the streams of the Gold Coast Hinterland, but in particular to assess the species’ capacity to act as an effective ecosystem engineer, obtain measures of the ecosystem services provided by the species, and evaluate the likely impacts of the crayfish on downstream water quality. To achieve this objective, an estimate of the population size of E. sulcatus was obtained; a series of experiments measured the species’ capacity to liberate nutrients from leaf litter, reduce the particle-size of the leaf litter, and mobilise and redistribute organic and inorganic materials in a flowing stream environment. This information allowed estimation of the species’ ecological impact(s) per unit time as a measure of the ecosystem services provided by E. sulcatus in the headwater streams of the study area. During this study E. sulcatus was common and abundant with a within-stream density of ~0.5 crayfish m-2. The total population of E. sulcatus in the study area was estimated at >860,000 crayfish. Correction for strong seasonal variation in activity was required for ecological impact calculations, and the “ecologically effective” population was estimated at >570,000 crayfish (biomass ~12 tonnes wet weight (WWT)). Crayfish significantly liberated nitrogen and phosphorus from leaf litter into the water column via consuming leaf litter and excreting nutrients. The phosphorus dynamic was complex, however the overall effect of crayfish was to facilitate eventual “loss” of phosphorus from the system with binding/absorption to substrates, particularly leaf litter, evident as the mechanism. The ecologically effective population was estimated to liberate at least 140 kg of nitrogen, 1.5 kg of phosphorus, and facilitate the loss of around 0.15 kg of soluble phosphorus from leaf litter per annum. Crayfish consumed large amounts of leaf litter while significantly reducing its particle-size. The ecologically effective population consumed at least 14 tonnes WWT of whole leaf litter, producing ~4.5 tonnes WWT of fine particles (<1 mm), with a nett consumption of ~9 tonnes WWT leaf litter per annum. The day-to-day activities of crayfish led to significant mobilisation and downstream export of materials 1 mm diameter, with about half this material of organic origin. The ecologically effective population facilitated the mobilisation and downstream export of around 90 tonne-meters (dry weight) material per annum. Given this annual crayfish-export effect is dramatically overwhelmed by the periodic flood spates in the area, it is unlikely crayfish-mediated export of materials is negative for downstream water quality. In the field it is anticipated that the liberated nutrients will be stripped from the water column by other biota, and/or abiotic processes, and eventually recycled back into and retained in the headwater ecosystems. Similarly, crayfish-mediated particle-size reduction of leaf litter will facilitate further processing by other biota, and recycling and retention of this material in the headwater regions. In the typical baseflow conditions, the instream mobilisation of materials will be positive for maintaining the high quality of water flowing from the headwater streams, by maintaining streambed complexity and ecological processes such as enhanced decomposition of organic detritus. Euastacus sulcatus is a common, abundant and ecologically aggressive species, and the results of this study support a conclusion that this species is an effective ecosystem engineer. The population of E. sulcatus clearly provides a number of ecosystem services, and even lower bound estimates indicate the magnitude of these services are fairly substantial at a local scale, and must be of appreciable benefit in maintaining the function and health of the headwater stream ecosystems.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Anthropogenic impacts such as fishing and eutrophication are significant challenges to the sustainable management of aquatic ecosystems. This study used two ecosystem modelling techniques to investigate the effects of fishing and eutrophication on aquatic ecosystems in Western Australia. Firstly, a qualitative modelling technique called ‘loop analysis’ or ‘qualitative modelling’ was used to characterise the dynamics of the seagrass ecosystem in Shark Bay, Western Australia (Chapter 2). A qualitative model based on differential equations, was developed to represent the dynamics of the seagrass ecosystem, particularly interactions among tiger sharks, megafauna (e.g. dugongs), and megafauna prey (Fig. 2.2). Although the model structure generated some uncertainty about model predictions and model stability, it was possible to assess the stability of the model and to determine the response signs of model variables by applying data and magnifying loops. Qualitative modelling analyses indicated a strong top-down control by tiger sharks and suggested that this controlling effect occurred in four stages. A step-by-step increase in tiger sharks (States 1 and 2) led to a habitat shift by the megafauna out of seagrass meadows and into safer, deeper channel habitat. A step-by-step decrease in tiger shark numbers led to the megafauna returning to seagrass meadows, leading to a decrease of megafauna prey in this habitat (steps 3 and 4). Thus, tiger sharks influenced the use of seagrass habitats by megafauna species through direct and behaviourally mediated impacts. Further, megafauna responses to tiger shark predation risk established alternating predation pressure on different prey groups within seagrass habitats. Curiously, despite the fact that only some megafauna species (e.g. dugongs) are major components of diet of the adult tiger sharks, the perceived predation risk created by the high abundance of of tiger sharks in summer appears sufficient to cause megafauna species to leave (or under-utilise) feeding habitats in seagrass meadows. Thus, the modelling results suggest that the abundance of tiger sharks exerts an important top-down, regulatory influence on the other ecosystem components. This regulatory system has the potential to become imbalanced if there is a decrease in the abundance of adult tiger sharks in Shark Bay, as has occurred tiger shark populations in other areas worldwide. Targeting of tiger sharks by fishers in the waters of Northern Australia and Indonesia has increased steadily during the last years and impact the tiger shark stock in Shark Bay if, as has been hypothesized, there is single common stock. A qualitative trophic model suggested that the activities of recreational fishermen within Shark Bay reduce prey availability for juvenile tiger sharks, an impact which might adversely affect the tiger shark population and, thus, the dynamics of this seagrass ecosystem. Evidence of the ecological importance of tiger sharks and the potential impact of a population decline emphasises the need to sustain the tiger shark population in Shark Bay. In the second part of this study, a quantitative modelling technique, Ecopath with Ecosim and Ecospace, was applied to the ecosystem of the Peel-Harvey Estuary, Western Australia. A key impact on this ecosystem is the the Dawesville Channel, an artificial entrance channel was constructed in the mid-1990s to increase the flushing and reduce nutrient concentrations in the estuary. Ecopath was used to analyse the impact of the Dawesville Channel on the estuarine ecosystem. A large dataset was collected for model development, a process that uncovered significant data gaps (e.g. missing data on detritus pool and dietary information and indicated important areas for further research (Chapter 3). Two identical Ecopath models (comprising 30 living functional groups) were otherwise developed for the Peel-Harvey Estuary to describe the state of the ecosystem before (‘pre DC’) and after (‘post DC’) the opening of the Dawesville Channel (Chapter 4). Modelling found that, in addition to changes in the community structure of plants, fish and invertebrates, the entire ecosystem of the Peel-Harvey Estuary has declined drastically in total biomass since the opening of the Dawesville Channel, as has the biomass at each trophic level and in the size of flows between the functional groups. Changes in flows and transfer efficiencies suggested a change in the functioning of the ecosystem in which consumption has become a more important and more efficient flow since the opening of the channel. Analysis of network and system statistics indicated that food web structure had also changed, with more linkages in the ‘post DC’ model and thus a more web-like structure than in the ‘pre DC’ model. Modelling also identified changes in cycling processes and suggested that the ecosystem in the ‘post DC’ model was not able to keep carbon within the system, even though: (i) the food web has developed more linkages and (ii) with less primary production and less cycling, the size of the ecosystem has decreased drastically since the channel opening. Overall, the results of the Ecopath modelling indicated that the Dawesville Channel has markedly impacted the features, functioning and services of the Peel-Harvey Estuary (Chapter 4). Several indices were applied that suggested that both the ‘pre DC’ and the ‘post DC’ models were highly immature. Ecopath was also applied to investigate the impact of the Dawesville Channel on ecosystem services. Ecopath modelling indicated that all ecosystem services had declined, such as provisioning services (catches), regulating services (CO2-Fixation) and supporting services (nutrient cycling, primary production and biodiversity). Unfortunately, it was not possible to locate data relating to cultural services (tourism) for the ‘pre DC’ model. To support the reliability of the Ecopath and Ecosim predictions, model uncertainty and the sensitivity of the parameter settings were assessed in detail (Chapter 5). Overall, the results of this analysis indicated that the parameter settings for the ‘pre DC and ‘post DC’ models were robust and did not lead to uncertainties regarding modelling results and predictions. However, the vulnerability settings are crucial for Ecosim and Ecospace and need to be treated with caution. Ecosim was applied to identify: 1) the impact and effectiveness of the selective reduction of different primary producers and 2) the impacts of fishing on target and non-target species on the ecosystem model (Chapter 6). The application of Ecosim requires fitting a model to time series data; for this study, the sourcing and fitting of time-series data indicated the importance and uncertainty of vulnerability settings. Three categories of vulnerabilities were identified: (a) vulnerabilities that did not have any effect on time series fitting (category 1); (b) interactions in which the lowest sums of squares occurred at low vulnerability settings (v=1 or 2, category 2); and settings that had a drastic impact on model fitting (category 3). The Ecosim simulations indicated that fishing affected almost all functional groups in the model, not just the target species. The recreational fishing sector also had a very strong impact on many functional groups, particularly Blue Swimmer Crabs and other invertebrate groups like bivalves and gastropods. The commercial fishing sector affected functional groups less than the recreational sector, but affected a range of estuarine fish groups including non-target fish species. Thus, the results of this study suggest that it may be not advisable to close those fleets completely as some aspects of the estuary ecosystem appear to benefit from increasing fishing pressure. Some fish groups and some target species responded positively to the closure of certain fleets, while others – particularly waterbirds and other top predators – did not (Table 6.8). Ecosim analyses highlighted the need for more data to ensure sustainable management, but suggested that the coexistence of fleets might be a better solution for sustaining catches and group biomasses in the future. Ecosim modelling indicated that selective plant removal is a reasonable management tool for this estuary. However, nutrient reduction and, thus, the permanent reduction of microscopic algae appears to be more ecologically and economically worthwhile (Fig. 6.12). Removing aquatic plant groups showed no significant longterm change in biomasses and the magnitude of short-term effects was much higher than for long-term effects. The Ecosim simulations demonstrated that only a permanent reduction in microscopic algae led to a reduction in total biomass. Reducing phytoplankton might be worthwhile because, although blooms of Nodularia spumigena no longer occur in the estuary because the salinities are too high (Huber, 1985), the estuary now contains several phytoplankton species (e.g. Heterosigma akashiwo) that cause blooms in other ecosystems (Guiry & Guiry, 2010). While the effects of phytoplankton blooms on the ecosystem depend on the size (i.e. the biomass) of the bloom, even blooms that only double the biomass of microscopic algae can have drastic long-term effects. This study supports the conclusion that a reduction in phytoplankton through management of nutrient input in the estuarine catchment represents the only ecological and economical management scenario that provides long-term sustainability for this ecosystem (Chapter 6). Ecospace modelling represents biomass dynamics over two-dimensional space and time. For this study, a model with fours habitats (shallow mud, deep sand, rocks and plant habitat) was developed. By applying Ecospace, the effects of reducing plant habitat and the effectiveness of two Marine Protected Areas were investigated, with specific consideration of waterbirds (Chapter 7). The Ecospace simulations suggested that waterbirds and piscivorous waterbirds were impacted by fishing and would benefit slightly from an introduction of a MPA, in particular a MPA at Point Grey. Further, the results of this Ecospace scenario indicated that waterbirds would profit from the reduction of plant habitat, whereas piscivorous waterbirds showed a small decline in biomass after removal of aquatic plants. Under the current fishing effort, the total biomass of the system and of the fish community increased. Thus, while the major prey groups of piscivorous waterbirds increased in biomass, but piscivorous waterbirds did not benefit from increased prey biomasses in the model, presumably because of the competition for fish. Ecospace modelling indicated that the catches would also increase drastically and, thus, that piscivorous waterbirds were in direct competition with the fishing sectors and other piscivorous predators (e.g. dolphins and sharks) and were out-competed for fish. The modelling suggest that the sustainable management of the fishing sectors is essential for bird conservation. A MPA at Peel Inlet led to lower catches under the current fishing scenario and catches declined even further under lower fishing effort. In contrast, after introducing a MPA at Point Grey, the total catch only declined when the fishing effort was lessened. The Ecospace simulations indicated that an MPA at Point Grey increased the biomasses of functional groups and target species and also raised the total biomass of the system; however, these effects strongly depend on fisheries management (Chapter 7). Overall, the qualitative and quantitative modelling methods applied in this study improved our understanding of the dynamics and functioning of the Shark Bay and Peel-Harvey ecosystems (Chapter 8). Both approaches produced robust and reliable results. If precise quantitative predictions are required for a management scenario, Ecopath with Ecosim is the appropriate method to choose, as this approach can deliver detailed changes in biomass and catches. In contrast, qualitative modelling only indicates the direction of change, which might not always satisfy management needs. However, qualitative models are the ideal method when management decisions have to be made fast and when a detailed data set of the ecosystem is not available.

Anthropogenic activities are often considered to be the main sources of mercury (Hg) found in aquatic systems. The aim of this study was to reconstruct the historic input of Hg to a large lake (Lake Ekoln) situated downstream the City of Uppsala using a dated sediment core. The main objective was to reveal general long-term (millennia-scale) trend in mercury loadings to the lake assess to what extent the lake has received an increase input of mercury during the last century from atmospheric inputs or local sources (mining activities, hospital effluents, industries or agricultural activities). Sediment samples were analyzed with X-ray fluorescence spectroscopy for measurements of lead and phosphorous (used as a proxy for atmospheric inputs and effluent water, respectively). Total Hg was analyzed using a mercury analyzer. My results indicate high Hg concentrations in sediment of Lake Ekoln during the last three centuries. Hg concentrations was not correlated to atmospheric derived metals (Pb) or effluent water derived nutrients (P) and only weakly correlated to the organic matter content of the sediment. Highest concentrations was found during a period around 1850 and in the last few years. The weak correlation with Pb suggest that the Hg is entering the lake from other sources than atmospheric inputs. The most likely local sources are argued to be mining activities (including fossil fuel burning during the production of iron) or Uppsala university hospital situated upstream of Lake Ekoln. However, there is a large uncertainty regarding the importance of these historical Hg sources for the lake.

Following the decline of the UK metal mining industry by the 1920s, over 3,000 abandoned metal mines exist in England and Wales. Contaminated drainage from this historical industry causes approximately 20% of all water quality failures in England and Wales. In this thesis, a holistic geographical approach, incorporating aspects of hydrology, hydrogeochemistry and freshwater ecology, is employed to investigate the hydrological, sedimentological and ecological impacts of the abandoned Dylife lead/zinc mine on the Afon Twymyn (central Wales). Examination of river sediment quality highlights the need for measurements of the quality of this component of the river ecosystem and, in particular, measurement of bioavailable as opposed to total metals. The majority of heavy metals in bed sediments of the Afon Twymyn exist in highly mobile geochemical phases, potentially posing serious threats to ecological integrity. Significant metal flushing occurred during flood events at Dylife mine and a distinct seasonal pattern was observed with greater levels of flushing occurring during flood events in the summer months. It is suggested that investigations of contaminant/ecosystem relations and potential remediation strategies should include high-resolution temporal sampling of river water chemistry under conditions of flood flow. Paradoxically, a range of biological indices failed to identify significant negative impacts of metal mine contaminants on macroinvertebrate communities, suggesting there is little contamination of the river ecosystem. However, Canonical Correspondence Analysis did identify significant differences in community structure between polluted and unpolluted river stretches, suggesting that standard unimetric biological indices might only be successful in identifying impacts at the most severely polluted mine sites. It is suggested that the ecological approach of the European Union Water Framework Directive to the assessment of river ecosystem status may not yield an accurate representation of contamination in rivers such as the Afon Twymyn where contamination by mining is moderate, circum-neutral and the mining operation is long abandoned.

Radionuclides are widely used in energy production and medical, military and industrial applications. Thus, understanding the behaviour of radionuclides which have been or may be released into ecosystems is important for human and environmental risk assessment. Modelling of radionuclides or their stable element analogues is the only tool that can predict the consequences of accidental release. In this thesis, two dynamic stochastic compartment models for radionuclide/element transfer in a marine coastal ecosystem and a freshwater lake were developed and implemented (Paper I and III), in order to model a hypothetical future release of multiple radionuclides from a nuclear waste disposal site. Element-specific mechanisms such as element uptake via diet and adsorption of elements to organic surfaces were connected to ecosystem carbon models. Element transport in two specific coastal and lake ecosystems were simulated for 26 and 13 elements, respectively (Papers I and III). Using the models, the concentration ratios (CR: the ratio of the element or radionuclide concentration in an organism to the concentration in water) were estimated for different groups of aquatic organisms. The coastal model was also compared with a 3D hydrodynamic spatial model (Paper II) for Cs, Ni and Th, and estimated confidence limits for their modelled CRs. In the absence of site-specific CR data, being able to estimate a range of CR values with such models is an alternative to relying on literature CR values that are not always relevant to the site of interest. Water chemistry was also found to influence uptake of contaminants by aquatic organisms. Empirical inverse relationships were derived between CRs of fish for stable Sr (CRSr) and Cs (CRCs) and water concentrations of their biochemical analogues Ca and K, respectively (Paper IV), illustrating how such relationships could be used in the prediction of more site-specific CRCs and CRSr in fish simply from water chemistry measurements.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Limitations from reduced light and increasing water depth on Nelumbo lutea seedlings were determined in tank experiments. Survival was high in all tested light levels. Total biomass increased significantly with increasing light. Biomass allocation shifted significantly to root production between 3 and 6 weeks in the 10 and 24% levels. Survival decreased with increasing planting depth, and biomass of survivors reduced significantly between 0.5, 1.0, and 1.5 m depths. Nelumbo lutea and Myriophyllum spicatum populations were monitored for one season in a 0.7 ha pond to track changes in species dominance. Myriophyllum spicatum dominated early, and N. lutea dominated from July through October, suppressing M. spicatum at all depths. Competitive interactions between N. lutea and M. spicatum were investigated for two seasons in a container experiment situated within a pond. Where established, N. lutea dominated in the presence of M. spicatum. However, N. lutea could not be established in depths greater than 1 meter.

Natural resources management is one of the world‟s greatest concerns. It is a difficult task due to its complex nature. Natural resources are limited and scarce. Unfortunately and worst of all, they are under pressure, and stress due to unprecedented increase in their demand and inefficient use. But it is still possible to tackle this complex problem. This study focuses on understanding the value of the ecosystem services that human well-being depend on, as for more sustainable environment strategy on aquatic ecosystems management, such as lakes and rivers. Changing behavior and attitude can be a crucial complement and likely can stimulate our conscious effort towards saving our ecosystems beyond money contribution. This way of thinking seems to be overlooked and most people think that the development of technology and advancement in knowledge alone can provide solution. One way to overcome the problem of pressure and stressing of the environment is to develop adequate strategy and environmental policy. This policy should include economics measures where, when necessary and feasible. Since there are "no one solution and no one answer" to achieve the desired outcome of a sustainable future, it becomes necessary to adopt a multidisciplinary approach to environmental management and the understanding of the value and dynamism change of the ecosystem services. Adoption of efficient management is not enough; we have to adjust our attitude as well. To discuss this issue, the aquatic ecosystem, which the lake Vänern in Kristinehamn Municipality served as a case study.

El presente estudio tiene como objetivo proporcionar una base de conocimiento sólida para la restauración ecológica de ríos, basada en la respuesta de comunidades acuáticas a cambios en la conectividad hídrica, factores medioambientales y presión antrópica. La conectividad hídrica lateral resultó ser el factor principal que estructura hábitats y comunidades acuáticas en el Ebro; mientras que la turbidez, salinidad y concentración de nutrientes fueron factores secundarios. La combinación de estos factores establece un marco ecológico que permite realizar predicciones acerca de los patrones taxonómicos y funcionales con más probabilidades de ocurrir en la llanura del Ebro. La posibilidad de que se creen nuevos humedales de forma natural en el Ebro es muy baja, mientras los que quedan están amenazados por una baja renovación del agua. El objetivo de la restauración ecológica debe por tanto consistir en re-establecer un amplio rango de condiciones hídricas, de acuerdo con el potencial sostenible del ecosistema.
The present study aims to provide a solid background for river-floodplain restoration based in the response of aquatic communities, to changes in hydrological connectivity, environmental factors and human pressure across the floodplain of a Mediterranean river.The lateral hydrological connectivity was found to be the key factor structuring the habitats and aquatic communities of the Middle Ebro floodplain, while turbidity, salinity and nutrient status were secondary drivers. These factors created a template for the aquatic community development that enabled predictions about the taxonomic and functional patterns in those aquatic communities more likely to occur under particular conditions. In the Middle Ebro River, there are very few possibilities of new wetlands creation, while the diversity and functionality of the remaining ones are threatened by the limited hydrological connectivity. The objective of floodplains restoration should thus consist in re-establishing a wide range of wetland types in accordance with the river-floodplain potential of sustainability.

Although it is well documented how introduced species can negatively affect native species, we only poorly understand how they may alter ecosystem functions. We investigated how an invasive fish affected the flux of aquatic insects to terrestrial food webs using mesocosms in a desert spring ecosystem. We compared aquatic insect emergence between alternative community states with monocultures and polycultures of two native species of fish, least chub (Iotichthys phlegethontis) and Utah chub (Gila atraria) plus, introduced western mosquitofish (Gambusia affinis). We tested three hypotheses: (1) aquatic insect biomass will be greater than terrestrial insect biomass and thus, constitute a vital source of energy for terrestrial consumers (2) invasive mosquitofish will negatively impact the biomass of emerging aquatic insects, and (3) terrestrial consumers will negatively respond to decreased emerging aquatic insect biomass. Aquatic insects represented 79% of the flying insect community, and treatments with mosquitofish significantly reduced emergent aquatic insect biomass by 60% relative to the control without mosquitofish. Behavioral traits of invasive species are important, because mosquitofish most heavily affected insects that emerged during the day. Also, spiders that build horizontal webs were negatively correlated with decreasing aquatic insect biomass. Invasive mosquitofish can achieve very dense populations because of their high intrinsic rate of population increase, which can significantly disrupt the flow of energy between aquatic and terrestrial ecosystems, thereby reducing the energy available for terrestrial consumers.

This study has contributed to the development of the reference condition approach in disturbed landscapes. The reference condition approach has been an important development for the bioassessment of aquatic ecosystems by providing a practical tool for the accurate assessment of river condition. The selection of appropriate reference sites is critical to the success of the predictive model in terms of being able to distinguish between natural variation in biota and the effects of human disturbance. Capturing natural variability and explaining it is a key difference between the reference condition approach and other study designs (e.g. before/after/control/impact). Natural disturbances such as drought or bushfire can significantly alter the ecological condition of streams, and although the ecological condition of streams affected by natural drought or bushfire is part of the natural cycle, this natural variation of the ecological condition is rarely incorporated into many study designs because of a mismatch in time scales. Human disturbance has also significantly altered the condition of landscapes through the development of agriculture and urbanisation. In urban or agricultural landscapes it can be impossible to locate streams that have not been modified by human activity for use as a reference condition. This study looked at the effects of natural disturbance on the reference condition, in terms of the way natural disturbance affects the prediction of stream condition and also the incorporation of the condition of streams experiencing natural disturbance into a predictive model. Additionally this study identified an alternative benchmark for modified landscapes based on the presence of good management practices for river protection, and tested this benchmark for the assessment of streams impacted by urbanisation. Drought and bushfire regularly disturb aquatic ecosystems in Australia, and affected reference sites in the ACT and South Coast region of New South Wales in 2002 and 2003. Drought and bushfire conditions affected macroinvertebrates and environmental variables across these streams, and the majority of sites were assessed as significantly impaired using regional AUSRIVAS (AUstralian RIVers Assessment System) models. This indicated the existing reference conditions for these regions had not incorporated the ecological conditions of reference sites suffering these natural disturbances. Many of the environmental variables used to predict the condition of streams were also affected by drought or bushfire. The changes to environmental variables affected how sites were assessed in models, but the overall assessment was not significantly changed from the initial assessment that drought or bushfire had significantly impaired the ecological condition. To reduce potential assessment errors associated with changes to predictor variables an attempt was made to construct new models with changeable variables excluded. However, it was not possible to completely exclude these types of variables, and subsequent models were no better than the original models in terms of changes to predictor variables affecting the generation of expected taxa lists. The changes to environmental variables did not affect the actual assessment of site condition because although group membership probabilities were changed the probabilities of taxon occurrence did not change significantly. The different reference site groups all contained some common taxa that occurred at most sites and even when group probabilities changed this did not change the probability of these taxa occurring at a test site. For regional models, such as the ACT or NSW South Coast, changes to predictor variables may not significantly affect the assessment of site condition. Incorporating reference sites under drought conditions into a predictive model was an effective way of discriminating the effects of drought from human disturbance. The model only provided two different ecological conditions, a single drought measurement and a single non-drought measurement, so the model did not fully encompass the potential natural variability. The model has value as a starting point and was effective in distinguishing sites affected by human disturbance from sites affected by drought. Good Management Practice (GMP) for river protection is any intervention that minimises human impact on stream condition. Urban sites protected by GMP were used as an alternative benchmark to a minimally impacted reference condition. The criteria used to select reference sites were not sufficiently robust to detect a significant benefit of GMP on physical or chemical characteristics of protected sites, compared to sites without GMP. In general however, the physical and chemical condition of GMP sites was better than sites without GMP and there were significant differences in macroinvertebrate assemblages of GMP and non-GMP sites. A refinement to the site selection process is proposed to include a specific assessment of GMP effectiveness for the protection it is designed to provide. This will substantially improve the robustness of a GMP benchmark and provide a clearer picture of the factors controlling biota in urban streams protected by GMP. The GMP benchmark was developed into a predictive model for the assessment of urban stream health, and in terms of the assessment of test site condition, it did not differ significantly from a model using minimally impacted sites. The purpose of the GMP benchmark was to provide an alternative reference condition for the assessment of stream health in modified landscapes when minimally impacted sites are unavailable or provide an unattainable benchmark. The GMP reference condition as an alternative can provide an attainable and realistic benchmark. The development and application of the suggested site selection protocol will improve the robustness of the GMP benchmark and better account for natural variation in the biota and physical characteristics of the sites used to determine the reference condition.

The introduction of lake trout Salvelinus namaycush into Yellowstone Lake preceded the collapse of the native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri population. As a system with a simple fish assemblage and several long-term data sets, Yellowstone Lake provided a unique opportunity to evaluate the ecology of a native salmonid in the presence of a non-native salmonid population undergoing suppression in a large natural lake. Diet data for Yellowstone cutthroat trout and lake trout were evaluated at varying densities to determine the effects of density on diet composition. Temporal diet shifts from 1996-1999 to 2011-2013 were likely caused by limitation of prey fish for lake trout. Diets, stable isotopes, and depth-related patterns in CPUE indicated lake trout > 300 mm consumed primarily amphipods, making them trophically similar to Yellowstone cutthroat trout from during 2011-2013. A lake trout removal program was initiated during 1995 to reduce predation on Yellowstone cutthroat trout. Abundance and fishing mortality were estimated for lake trout from 1998 through 2013 and Yellowstone cutthroat trout from 1986 through 2013. Density-dependence was evaluated by examining individual growth, weight, maturity, and pre-recruit survival as a function of abundance. In addition, a simulation model was developed for the lake trout-Yellowstone cutthroat trout system to determine the probability of Yellowstone cutthroat trout abundance persisting at performance metrics given potential reductions in lake trout abundance. Estimates of Yellowstone cutthroat trout abundance varied 5-fold and lake trout abundance varied 6-fold. Yellowstone cutthroat trout weight and pre-recruit survival decreased with increasing Yellowstone cutthroat trout abundance; however, individual growth and maturity were not related to abundance. Lake trout population metrics did not vary with lake trout abundance. Simulation model results were variable because of uncertainty in lake trout pre-recruit survival. Conservative estimates for required lake trout reductions were > 97% of 2013 abundance for a > 70% probability of Yellowstone cutthroat trout persistence at the performance metrics outlined in the Native Fish Conservation Plan. Lake trout removal will likely reduce lake trout abundance and result in Yellowstone cutthroat trout recovery if the amount of fishing effort exerted in 2013 is maintained for at least 15 years.

A study of macroinvertebrate colonization and assemblages, including secondary productivity of the familiar bluet damselfly or Enallagma civile Hagen (Odonata: Coenagrionidae), associated with the aquatic macrophytes Heteranthera dubia (Jacq.) MacMill. (water stargrass) and Potamogeton nodosus Poir. (American pondweed) was conducted at the Dallas Floodway Extension Trinity River Project (DFE) Lower Chain of Wetlands (LCOW), Dallas, TX, from September 2010 through November 2011. Macroinvertebrate abundance, taxa richness, Simpson's index of diversity, and Simpson's evenness from the two macrophytes and from three different wetland cells of varying construction completion dates, water sources, and native aquatic vegetation establishment were analyzed along with basic water quality metrics (temperature °C, pH, dissolved oxygen mg/L, and conductivity µs/cm). E. civile nymphs were separated into five developmental classes for secondary productivity estimations between macrophytes and wetland cell types. Mean annual secondary productivity in the DFE LCOW among two macrophytes of E. civile was 1392.90 ash-free dry weight mg/m²/yr, standing stock biomass was 136.77 AFDW mg/m2/yr, cohort production / biomass (P/B) ratio was calculated to be 4.30 / yr and the annual production / biomass (P/B) ratio was 10.18 /yr.

Mestrado em Engenharia do Ambiente - Gestão Ambiental - Instituto Superior de Agronomia
With the main aim of verifying whether Daphnia magna is sufficient for the evaluation of the environmental risk of pesticides to aquatic ecosystems, toxicity values of 218 insecticides were analyzed. For each one the relative tolerance (Trel) value was calculated to compare the sensitivity of species from different taxonomic groups with that of D. magna. The taxonomic groups were grouped in arthropods, non-arthropod invertebrates, fish, algae/macrophytes and based on Trel values the species sensitivity distribution (SSD) were defined. For the arthropods the influence of the mode of action (MOA) on vulnerability to the insecticide was also analyzed. Still in the arthropods group, for each species, the class, order and family they belong to were identified. To check the necessity of inclusion of a second species studies of relationship were performed, between D. magna, Americamysis bahia and Chironomus riparius. As far as the SSD curves are concerned, for the different groups the most sensitive one was the arthropods group in both values of EC50 and NOEC. Taking into consideration MOA the group of neonicotinoids was the most sensitive one in EC50 case and the GABA – gated chloride channel antagonists in NOEC. The most sensitive taxonomical group was Mysida and it was the combination of Daphnia plus A. Bahia that generated the greater percentage of protection.

Peatlands are wetlands where gross primary production exceeds organic matter decomposition causing an accumulation of partially decomposed matter, also called peat. Peat ecosystems can accumulate more carbon (C) than tropical rainforests. However, dissolved fluxes of C (as dissolved organic carbon (DOC), carbon dioxide (CO₂) and methane (CH₄)) must also be considered to determine if these ecosystems are net sinks or sources of greenhouse gases (GHGs) to the atmosphere. This research was conducted in Burns Bog, Delta, BC, Canada, one of the largest bogs on the west coast of the Americas, but which has been heavily impacted by a range of human activities. Currently, ecological restoration efforts are underway by a large-scale ditch blocking program, with the aim of re-establishing water table conditions that promote peat accumulation. Here I present data on ecosystem-scale fluxes of CO₂ and CH4 determined by eddy covariance (EC), together with data on (i) evasion fluxes of CO₂ and CH₄ from the water surface, and (ii) the flux and characteristics of DOC in water draining Burns Bog. The net ecosystem carbon balance (NECB) was determined as the sum of EC fluxes and DOC export. Concentrations of dissolved CO₂ and CH₄ were determined by headspace equilibration, and evasion rates from the water surface were quantified and used to estimate the role of the hydrosphere in the ecosystem-scale measurements. Water samples collected from five saturated areas in the flux tower footprint were analyzed for DOC concentrations and characteristics. Satellite imaging showed that during the dry season 10% of the area was covered by water, while on the wet season, it was 60%. The hydrosphere was found to be a continual C source, emitting 271 g C m-² yr-¹. NECB was found to be -98 g C m-² yr-¹. DOC export was found to offset about 60% of the apparent net C emissions determined by EC during the wet season and 3% of the net C uptake during the dry season, indicating that the EC measurements by themselves underestimate C emissions during the wet season and overestimate C accumulation in the dry season by not accounting for DOC drainage.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The level of alteration in response to the same level of exposure can vary greatly among different ecosystems: in particular, effects provoked by chemicals are not only relying on their “absolute toxicity” and on their concentration, but also on the ecological vulnerability of the system. Vulnerability is often overlooked in current risk assessment procedure, but its knowledge is pivotal in site-specific studies, where the object of the protection is shifted from a generic scenario to a real ecological system. The study of ecological vulnerability confirms that risk assessment, as becoming site-specific, needs more ecological knowledge. In this path, the use of ecological and biological traits of organisms has proven to be a promising approach to evaluate the ecological vulnerability at different level of biological organization. In this work the issue of the ecological vulnerability has been considered from several different perspectives, using multiples methodologies and working at completely different scales. The leading thread is to show how an ecologically based approach can enhance our understanding of environmental processes and thus improving risk assessment methodologies.

The transfer of prey resources between ecosystems can have dramatic consequences for both recipient and donor systems by altering food web stability and the likelihood of trophic effects cascading across the ecosystem boundary. Landscape-scale factors influence the importance, direction and magnitude of energy flows, but may also alter the ability of consumer organisms to respond to spatio-temporal changes in allochthonous prey availability. Here, I used flood and drying disturbance gradients to investigate interactions between these two processes on populations of a riparian fishing spider Dolomedes aquaticus (Pisauridae). The abundance of aquatic insects with a winged adult stage, a major component of the diet of D. aquaticus, was markedly higher at less flood-prone rivers and declined with increasing flood disturbance. It was expected that spider populations would be largest at these stable rivers where the aquatic prey abundance was highest. However, a habitat (loose, unembedded riverbank rocks) manipulation revealed that the lack of scouring floods at these sites led to habitat-limited populations, preventing response to the increased prey resource. In fact a peak shaped relationship of spider biomass and abundance was found, with the largest spider populations at intermediately disturbed rivers. In addition, patchy habitat availability was the most likely cause of the small scale (4 m2) aggregation of spiders seen at the most stable and disturbed rivers. These patterns were also associated with strong interactions between the spiders. Stable isotope analysis of field collected spiders and an experimental manipulation of spider densities and food availability indicated that cannibalism rates were likely to be significantly higher at stable and disturbed rivers than those intermediate on the disturbance gradient. Differences in D. aquaticus population size structure and life history traits across the flood disturbance gradient were driven by interactions between resource availability, environmental stability and cannibalism rates. To separate the effects of habitat availability and aquatic prey abundance I used drying rivers, as the amount of aquatic insect prey alters as the water recedes. Desiccation mortality and low aquatic prey biomass most likely caused the spiders' spatial distribution and size class structure to alter in drying river reaches, potentially also leading to differences in cannibalism rates. Overall, cross-ecosystem transfers of prey had large impacts on the distribution, cannibalism rates and life history traits of D. aquaticus but their effects were modified by the nature of the ecosystem boundary. Thus river flow regime controlled the magnitude of the subsidy and its use by a consumer. Hence, cross-ecosystem subsidies will not always lead to larger consumer populations and consumer responses will depend on interactions between large-scale processes.

Little is known about the spatial distribution and abundance of tree holes in New Zealand’s native forests, or the invertebrate communities that they support. I found that tree holes were common on five endemic tree species, belonging to the families Fagaceae and Podocarpaceae in the mixed broadleaf-podocarp rainforest of Orikaka Ecological Area, Buller District, New Zealand. However, tree holes were not uniformly distributed throughout the forest, with more holes found on the three podocarp species, Prumnopitys ferruginea, P. taxifolia and Dacrycarpus dacrydioides, than on Nothofagus fusca or N. menziesii. Nevertheless, Nothofagus fusca had the largest holes of any of the tree species sampled and larger trees generally had larger holes. Large, hole-bearing Nothofagus fusca trees support a specialist hole-dwelling vertebrate fauna in New Zealand and worldwide, tree holes provide habitat for a range of invertebrate species. Using specially-designed emergence traps, I collected invertebrates emerging from naturally-occurring dry tree holes and compared this assemblage with invertebrates inhabiting leaf litter on the forest floor and those dispersing aerially throughout the study area. At the higher taxonomic resolution (i.e., Order or Class), community composition within the tree holes was highly variable, and there was no strong distinction between invertebrates from tree holes, leaf litter or Malaise traps. Moreover, although some beetle species emerging from tree holes were found exclusively in tree holes, most of these were represented by a single individual. Consequently, only minor differences in species composition were detected between beetle assemblages from tree holes, leaf-litter and those aerially dispersing throughout the forest. In contrast, the aquatic invertebrate assemblage within water-filled tree holes was highly distinctive from that in ground-based freshwater ecosystems, with only six aquatic taxa in common between all freshwater habitats. Using experimental water-filled tree-hole microcosms, I found that species richness and community composition within these microcosms were primarily driven by resource concentration, although habitat quality (i.e., water chemistry parameters) was also an important determinant of the identity and composition of colonising species. Overall, my study has shown that tree holes are common in the study area, and are likely to be more abundant in New Zealand’s indigenous forests than previously thought. Moreover, these generally small, discrete forest ecosystems support a diverse array of terrestrial invertebrates as well as a distinctive aquatic invertebrate community that is primarily structured by organic matter resource availability. These findings not only represent an important advance in our knowledge of New Zealand’s freshwater invertebrate biodiversity, but also highlight the need for further investigation into these unique forest canopy habitats which may well be at risk from deforestation and land use change.

Forests are an important component of the global carbon (C) cycle and contribute to climate change mitigation through atmospheric C uptake and storage in biomass and soils. However, the forest C sink is susceptible to disturbance, which modifies physical and biological structure and limits spatial extent of forests. Unlike severe, stand-replacing disturbances that reset forest successional trajectories and may simplify ecosystem structure, moderate severity disturbances may instead introduce complexity in ways that sustain net primary production (NPP), leading to the phenomenon of “NPP resilience.” In this study, we examined the linkage between disturbance severity and ecosystem biological and physical structural change, and implications for NPP within an experimentally disturbed forest in northern Michigan, USA. We computed spatially resolved and spatially agnostic metrics of forest biological and physical structure before and 10 years after disturbance across a continuum of severity. We found that while biological structure did not change in response to disturbance, three of four physical structural measures increased or were unimodally related to disturbance severity. Physical structural shifts mediated by disturbance were not found to directly influence processes coupled with NPP. However, decadal changes in the spatial aggregation index of Clark and Evans, though not a function of disturbance severity, were found to predict canopy light uptake, leaf physiological variability, and relative NPP within plots. We conclude that ecosystem structural shifts across disturbance severity continua are variable and differ in their relationship to NPP resilience.

Sediment Quality Guidelines (SQGs) serve as scientific benchmarks, or reference points of chemical contaminants levels for evaluating the possibility of occurrence of adverse biological responses in the aquatic environment. SQGs are important because the quality of sediment has significant influences on the health of aquatic organisms, and the use of SQGs is a critical means to protect and manage various aquatic ecosystems. In this study, nine conventional derivation methods are described and contrasted. Their uses and limitations, which in general reduce the ecological relevance of SQGs in applications, are discussed. Improvements can be made through implementing elements like site-specific, field-based, chemical mixtures assessments, etc. in the SQG derivation process. The Hong Kong sediment management system, which focuses on classification of dredged sediment for their disposal options, is reviewed. I suggest that the current system shall be subject to major review. First, SQG values (i.e., LCEL and UCEL) shall be reviewed with the establishment of a new database. Second, a new set of guidelines shall be derived site-specifically for the disposal area. Third, the chemical priority list shall be expanded to include other contaminants of environmental concerns. Forth, a tier of evaluating bioavailability of the target contaminant can be incorporated in the classification framework in order to assess the portion of chemicals that causes toxicity in the sediment. Finally, the biological test can be improved by using ecologically relevant local species. The need of the site-specificity in SQG derivation is justified in this study, by deriving two sets of SQGs (i.e., ERL, ERM, TEL, PEL and AET) using data from two geologically distinct areas in Hong Kong, which are the Hong Kong-Zhuhai-Macao Bridge (HZMB) area and the Kai Tak development area. The derived SQGs of arsenic, chromium, nickel and zinc are higher in the HZMB areas, but those of copper, mercury, lead and silver are higher in the Kai Tak area. In addition, the incidence rates of effect data with the same contaminants concentrations are different between the HZMB and Kai Tak area. The discrepancies among the derived SQGs and the incidence rates indicate that site-specific SQGs are essential. Furthermore, the analysis of incidence rates of effect data with different contaminants concentrations shows that the HKSQG (i.e., LCEL and UCEL) has to be reviewed, especially for arsenic, because high toxicity is not resulted at a high arsenic concentration range in the dataset.
published_or_final_version
Environmental Management
Master
Master of Science in Environmental Management

Diel dissolved oxygen (DO) data were used to characterize seasonal, inter-annual, and longitudinal variation in production and respiration for the James River Estuary. Two computational methods (Bayesian and bookkeeping) were applied to these data to determine whether inferences regarding DO metabolism are sensitive to methodology. Net metabolism was sensitive to methodology as Bayesian results indicated net heterotrophy (production < respiration) while bookkeeping results indicated net autotrophy (production > respiration). Differences in net metabolism among the methods was due to low seasonal variation in respiration using the Bayesian method, whereas bookkeeping results showed a strong correlation between production and respiration. Bayesian results suggest a dependence on allochthonous organic matter (OM) whereas bookkeeping results suggest that metabolism is dependent on autochthonous OM. This study highlights the importance in considering the method used to derive metabolic estimates as it can impact the assessment of trophic status and sources of OM supporting an estuary.

Baltic archipelago areas have high nature values despite being polluted from various antrophogenic activities within the Baltic Sea catchment area and from long-range transport of airborne substances. The discovery of environmental problems in the Baltic Sea in the 1960s led to countermeasures that gradually gave results in reducing the toxic pollution, e.g. from PCBs. Today, much of the environmental management is focused on reducing the effects of eutrophication. There is a demand from society on science to develop strategies that can direct remedial actions so that the cost-effectiveness is maximised. This work focuses on how mass-balance models can be used to understand how coastal ecosystems are controlled by abiotic processes and to predict the response to changes in loading of different substances. Advection, sedimentation and burial are examples of general transport processes that are regulated by morphometrical characteristics, e.g. size, form, effective fetch and topographical openness. This is why different coastal areas have different sensitivity to loading of pollutants. A comparison of six phosphorus and chlorophyll models of different complexity showed that the model performance was not improved with more state variables of total phosphorus (TP) than two water and two sediment compartments. Modelling chlorophyll as a separate state variable did not improve the results for individual values compared to a simple regression against total phosphorus in surface water. Field investigations of the phosphorus content in accumulation sediments along the coast of Svealand showed a distribution pattern that probably is related to differences in the redox status. The average content of mobile phosphorus was much higher than previously found in offshore Baltic sediments indicating that sediments may play an important role for the phosphorus turnover in Baltic archipelago areas. A one-year field study to measure the levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in water, sediments and fish during different seasons was carried out in Kallrigafjärden Bay. The collected data set was used to test a mass-balance model for PCCD/F-turnover. It was possible to reproduce the concentrations of different PCDD/F-congeners with high accuracy using a general model approach, including one water compartment and two sediment compartments, indicating that the applied model has the necessary qualifications for successful predictions of PCDD/F-turnover in Baltic coastal areas.
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