Os estudos apresentados nesta tese tiveram como objetivo compreender aspectos da organização de assembleias de algas bênticas em riachos. Foi avaliado especificamente o efeito da heterogeneidade de habitat na escala de rugosidade de substratos e sua interação com distúrbios hidrológicos e organismos pastejadores (grazers). Utilizou-se uma abordagem experimental in situ com substratos lisos e rugosos (com fendas) constituindo os tratamentos. Os experimentos foram conduzidos no Rio do Marco, um riacho de quarta ordem na região dos Campos de Cima da Serra, em São José dos Ausentes, Rio Grande do Sul. Após uma introdução geral acerca do assunto são apresentados os capítulos com os estudos. O Capítulo 1 avaliou os efeitos da rugosidade de substratos sobre a riqueza de espécies, densidade, composição e padrões de distribuição de assembleias de algas bênticas. Assembleias em substratos rugosos foram mais ricas que assembleias em substratos lisos, porém esse resultado diferiu entre grupos com diferentes formas de vida, assim como as diferenças na composição de espécies, indicando que somente alguns grupos foram beneficiados pela ocorrência de refúgios em substratos rugosos. Observou-se também que diferenças na composição da assembleia entre substratos lisos e rugosos resultaram de aninhamento e substituição de espécies. No Capítulo 2 foi testada a hipótese de que substratos rugosos abrigam assembleias mais persistentes que substratos lisos. Os resultados encontrados confirmaram esta hipótese e foram atribuídos ao efeito da rugosidade per se após a exclusão de alguns fatores de confundimento, como estabilidade física dos substratos e diferenças na riqueza de espécies. Concluiu-se que o mecanismo mais plausível para explicar a maior persistência em substratos rugosos é a maior disponibilidade de refúgios em relação a substratos lisos. O objetivo do Capítulo 3 foi avaliar o efeito da rugosidade de substratos sobre assembleias de algas frente a um distúrbio hidrológico experimental, testando especificamente se a resistência e a resiliência de algas é maior em substratos rugosos que em substratos lisos e se a resposta de diferentes formas de vida é distinta. Os resultados indicaram que a rugosidade de substratos não apresenta efeitos pronunciados sobre a resistência e a resiliência de algas bênticas. Porém, grupos de algas com distintas formas de vida diferiram quanto à resistência e resiliência, de forma que o padrão observado está relacionado a atributos biológicos que conferem habilidades para suportar distúrbios. Os resultados deste estudo em conjunto com os resultados obtidos no Capítulo 2 e resultados obtidos por outros autores permitiram que fosse proposto que a importância da heterogeneidade de habitas e de refúgios é mediada pela intensidade de distúrbios. No Capítulo 4 foram avaliados os efeitos independentes e as interações de rugosidade de substratos, peixes pastejadores e tipos de mesohabitats (corredeiras e remansos) sobre a biomassa algal, matéria orgânica e peso seco total. O efeito de peixes pastejadores não foi mediado pelos mesohabitats, sendo que a exclusão de peixes causou aumento nas três variáveis resposta, independente do tipo de mesohabitat. Por outro lado, houve uma interação entre mesohabitats e substratos para determinar o acúmulo de peso seco total, sendo que substratos rugosos acumularam maior quantidade de material em remansos que em corredeiras, enquanto substratos lisos acumularam quantidades similares entre os dois tipos de mesohabitats. Já a biomassa algal e matéria orgânica apresentaram maior acúmulo nos substratos rugosos em relação aos lisos, independente do mesohabitat. Os resultados encontrados indicam que a perda de organismos pastejadores pode afetar o acúmulo de biomassa algal e material orgânico, importantes recursos alimentares em riachos. Finalmente, na última seção são apresentadas as considerações finais. / The studies presented in this thesis aimed at understanding some aspects of the organization of benthic algal assemblages in streams. Specifically, the studies evaluated the effect of habitat heterogeneity on the scale of substrate roughness and its interaction with hydrological disturbances and grazing organisms. An experimental in situ approach was used, in which the treatments were constituted by smooth and rough (with crevices) substrates. The experiments were conducted in the Marco River, a fourth-order stream at the region of Campos de Cima da Serra, São José dos Ausentes, Rio Grande do Sul, Brazil. After a general introduction on the subjects of this thesis, the chapters with the studies are presented. The Chapter 1 describes a study to evaluate the effects of substrate roughness on species richness, density, composition and distribution patterns of benthic algal assemblages. Algal assemblages on rough substrates were richer than on smooth substrates, but this result differed among algal life forms. Similarly, results on species composition also differed among life forms, indicating that only some groups were benefited by the occurrence of refuges on rough substrates. It was also observed that differences in the composition of assemblages between rough and smooth substrates resulted from nestedness and turnover. The Chapter 2 describes a study in which was tested the hypothesis that rough substrates harbor more persistent assemblages than smooth substrates. The results confirmed this hypothesis and were attributed to the effect of roughness per se after the exclusion of some confounding factors, such as the physical stability of substrates and differences in species richness. It was concluded that the most plausible mechanism that could explain the higher persistence in rough substrates is the greater availability of refuges in relation to smooth substrates. The main aim of the study described in Chapter 3 was to evaluate the effect of substrate roughness on algal assemblages in the face of an experimental hydrological disturbance. Specifically, it was tested if the resistance and resilience of algae is higher on rough than on smooth substrates and if algal life forms differ in their response to disturbance. The results indicated that substrate roughness had no pronounced effects on benthic algal resistance and resilience. However, algal life forms differ in their resistance and resilience, and the observed pattern was mostly related to biological traits that confer abilities to support disturbances. The results of this study, in addition to the results obtained in Chapters 1 and 2, allowed us to suggest that the importance of habitat heterogeneity and refuges is mediated by the intensity of disturbances. The Chapter 4 describes a study that evaluated the independent and interacting effects of substrate roughness, grazing fish and mesohabitats (pools and riffles) on algal biomass, organic matter and total dry mass accrual. The effect of grazers was not mediated by mesohabitats, and their exclusion caused an increase in the three response variables, regardless of mesohabitat. On the other hand, mesohabitats and substrates interacted to determine the accrual of total dry mass, since rough substrates accumulated greater amounts of dry mass in pools than in riffles, while smooth substrates accumulated similar amounts in both mesohabitats. Algal biomass and organic matter showed greater accrual on rough than on smooth substrates, independently of mesohabitat. These results indicate that the loss of grazers may affect the accrual of algal biomass and organic matter, which are important food resources in streams. Finally, in the last section are presented the concluding remarks.

Submitted by (ana.araujo@ufrpe.br) on 2016-08-01T19:24:52Z No. of bitstreams: 1 Leda Valeria Ramos Santana.pdf: 2437098 bytes, checksum: f1ab02f82d16ec8b95e0800f78ab7585 (MD5) / Made available in DSpace on 2016-08-01T19:26:38Z (GMT). No. of bitstreams: 1 Leda Valeria Ramos Santana.pdf: 2437098 bytes, checksum: f1ab02f82d16ec8b95e0800f78ab7585 (MD5) Previous issue date: 2014-02-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Wind speed distribution depends on relief of a certain region, in the case of Brazilian Northeast (NE) there are four subregions with different characteristics of relief: Atlantic Rainforest zone, Agreste, North-Eastern Backlands and Northeast Mid North. Among probability distributions that were proposed for wind data, Weibull, General-ized Gamma and Rayleigh distributions were found to be most appropriate to model wind speed variability in many locations. In this work we analyze ERA-40 data, during the period 1958-2001, to evaluate which probability distribution is most suitable to describe temporal variability of wind speed in NE. ERA-40 is a re-analysis of meteor-ological observations from September 1958 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The data were produced using different sources such as radiosondes, ocean buoys, satellites and meteorological stations, and have temporal resolution of 6h and spatial resolution of 2.5ox2.5º. The two parameter Weibull distribution is found to be the best for modeling frequency distribution of wind speed data for most of the NE. The coastal zone is characterized by strongest winds and smallest temporal variability. These results can be used to evaluate the wind energy potential at NE and the influence of wind on various environmental phenomena as soil erosion, rainfall, dune formation and dispersion of seeds and poluents. / A distribuição da velocidade do vento depende do relevo de uma determinada região, no caso do Nordeste brasileiro são quatro sub-regiões com características de relevo distintas: Meio Norte, Sertão, Agreste e Zona da Mata. Entre as distribuições de probabilidade que foram propostas para dados de vento, a distribuição Weibull, Gama Generalizada e a Rayleigh são consideradas as mais apropriadas para modelar a variabilidade da velocidade do vento em muitos locais. Neste trabalho foram analisados dados da ERA-40, durante o período 1958-2001, para verificar que distribuição de probabilidade é mais adequada para descrever a variabilidade temporal da velocidade do vento no NE. A ERA-40 é uma re-análise de observações meteoro-lógica de Setembro de 1958 a Agosto de 2002 produzida pelo European Centre for Medium-Range Weather Forecasts (ECMWF) em colaboração com muitas institui-ções. Os dados são produzidos usando diferentes fontes tais como radiossondas, boias oceânicas, satélites e estações meteorológicas. E tem resolução temporal é de 6 h e espacial de 2.5º x 2.5º. A distribuição Weibull de dois parâmetros é considera-da a melhor para modelar a distribuição de frequência dos dados da velocidade do vento para a maior parte do NE. A faixa litorânea é caracterizada por altas velocidades e baixa variabilidade temporal. Estes resultados podem ser usados para avaliar o potencial eólico do NE e, a influência do vento sobre vários fenômenos ambientais como erosão do solo, precipitação, formação de dunas, dispersão de sementes e poluentes.

Esta pesquisa foi desenvolvida nas lagoas facultativas das estações de tratamento de esgoto dos municípios de Pariquera-Açu (PA) e Jacupiranga (JA), com diferentes configurações, sendo a primeira composta por lagoa anaeróbia seguida de facultativa com chicanas e a outra por lagoa aerada mecanicamente seguida de facultativa. Estas lagoas são consideradas ambientes hipereutróficos, pois apresentam grande quantidade de matéria orgânica oriunda dos esgotos domésticos e industriais. O conhecimento da estrutura da comunidade fitoplanctônica e sua avaliação em diferentes horários do fotoperíodo são relevantes pois estes organismos são responsáveis pela produção de oxigênio necessário para a degradação da matéria orgânica. Esta pesquisa teve como objetivo principal o estudo sazonal e diário da estrutura da comunidade fitoplanctônica e da produção primária nestas lagoas. Para atingir este objetivo foi caracterizada a estrutura da comunidade, em relação a biomassa e diversidade, e determinada a produção primária com incubações in situ através do método do oxigênio dissolvido. O estudo foi realizado em quatro épocas do ano (variação sazonal) no período das 7 às 16 horas, com amostragens de 3 em 3 horas (diária). Não foram observadas variações temporais e espaciais na estrutura da comunidade fitoplanctônica nas duas lagoas facultativas. Apenas as cianobactérias (principalmente a Synechocystis aquatilis e Phormidium sp) e clorofíceas (Kirchneriella lunaris, Chlorella Kessleri, Monoraphidium contortum, Monoraphidium sp, Chlamydomonas sp, Eutetramorus planctonicus e Micractinium pusillum) foram predominantes, nestas lagoas, porém em períodos alternados. Foram observados altos valores de produção primária bruta (15.891 mg\'O IND.2\'/\'M POT.3\'.h em PA; 5.700 mg\'O IND.2\'/\'M POT.3\'.h em JA) na interface água-sedimento das duas lagoas devido, provavelmente, ao padrão de mistura da coluna de água. Foram também observados altos valores de respiração da comunidade (abril, julho e setembro), devido à alta concentração de matéria orgânica presente nestes sistemas e, portanto, maior decomposição, indicando predominância de processos heterotróficos. / This research was developed in facultative ponds of the waste water treatment plant of Pariquera-Açu and Jacupiranga cities with different configurations, being the first composed by anaerobic pond followed by facultative with chicanas and the another composed by aerated mechanic pond followed by facultative. These ponds are considered hypereutrophic environments because it shows a large quantity of organic matter derived from the domestic and industrial sewage. The knowledge of phytoplanktonic community structure and its evaluation in different times of photoperiod are relevant since such organisms was responsible by production of oxygen necessary to the degrade of organic matter. This research had the main goal the seasonal and daily study of the phytoplanktonic community and the primary production in these ponds. To reach this objective the structure of the community was characterized in relation to biomass and density, and determined the primary production with incubations in situ through the dissolved oxygen method. The study was made in four periods of the year (seasonal variation) between the 7 a.m. to 4 p.m., with samplings of 3-to-3 hours (daily). It was not observed temporal and spatial variations in the phytoplanktonic community structure in the facultative ponds. Only cyanobacteria (mainly Synechocystis aquatilis and Phormidium sp) and chlorophycea (Kirchneriella lunaris, Chlorella Kessleri, Monoraphidium contortum, Monoraphidium sp, Chlamydomonas sp, Eutetramorus planctonicus and Micractinium pusillum) were predominant in these ponds, however, in alternated periods. It was observed high rates of gross primary production (15891 mg\'O IND.2\'/\'M POT.3\'.h, PA; 5700 mg\'O IND.2\'/\'M POT.3\'.h, JA) in the interface water-sediment of both ponds due, probably, to the standard of mixed conditions of water column. It was also observed high rates of community respiration (April, July and September), due to the high concentration of organic matter present in these systems and, therefore, greater decomposition, indicating predominance of heterotrophic processes.

Le compartiment phytoplanctonique joue un rôle prépondérant dans les écosystèmes marins de par sa position comme principal producteur primaire et fixateur de carbone, mais aussi en raison de sa capacité de multiplication élevée, qui lui permet de réagir rapidement aux changements environnementaux et d'en faire un potentiel bio indicateur. La plupart des études antérieures ne se sont basées que sur des observations réalisées à basse fréquence, ou bien ne ciblant qu'une partie des groupes/espèces phytoplanctoniques entraînant une perte importante d'information sur la variabilité d'abondance et composition du phytoplancton. Cette thèse a été réalisée dans le cadre du projet européen transfrontalier DYMAPHY dont l'objectif principal visait à améliorer les connaissances et l'évaluation de la qualité des eaux marines de la Manche et de la Mer du Nord, à travers l'étude de l'ensemble du compartiment phytoplanctonique et ses paramètres complémentaires. Dans ce contexte, une approche à haute fréquence et/ou haute résolution spatiale, via l'utilisation de la cytométrie en flux semi-automatisée, a permis de mieux caractériser la variabilité spatiale et temporelle du phytoplancton en Manche Orientale. Pour cela on a utilisé 3 approches complémentaires dont les résultats principaux obtenus lors de ce travail de thèse sont les suivants : (i) une étude à haute fréquence, avec une analyse cytométrique toutes les 10 minutes, qui a permis de révéler une forte variabilité spatiale du phytoplancton, à une échelle régionale (Manche Orientale), dont l'assemblage communautaire n'était pas déterminé par l'hydrologie ; (ii) un suivi saisonnier de l'ensemble du spectre de taille des cellules phytoplanctoniques le long d'un gradient côte-large proche du détroit du Pas de Calais, qui a révélé, au-delà d'une certaine hétérogénéité spatiale, une forte variabilité temporelle permettant de définir les successions saisonnières et les principaux facteurs les régissant, à savoir la luminosité et la concentration en sels nutritifs ; (iii) un suivi de 3 ans sur un point fixe en eaux côtières, qui a permis de mettre en relation les traits de vie des groupes phytoplanctoniques avec l'environnement, afin de comprendre comment les communautés phytoplanctoniques s'assemblent en réponse à la variabilité environnementale. Les résultats ont montré une différenciation fonctionnelle liée à l'utilisation des ressources et des stratégies de croissance, associées à un gradient de ressources. Cette étude confirme notamment l'importance de "l'hypothèse du ratio de masse", qui prédit que les traits de vie de l'espèce la plus abondante au sein d'une communauté, seraient le moteur des processus les plus importants au sein d'un écosystème. / Phytoplankton micro-organisms play a key role in marine ecosystems as main primary producers, being responsible for most of carbon uptake, but also due to their fast division rates which allow them to effectively react to environmental changes and which make them potentially good bio-indicators. Most previous studies have based their observations on low frequency sampling, only considering one fraction of phytoplankton communities, resulting in a significant loss of information on the dynamics of phytoplankton abundance and diversity. This thesis was carried out in the frame of the European cross-border DYMAPHY project, which main objective was to improve the understanding and the evaluation of the quality of marine waters in the English Channel and the North Sea, through the study of the whole phytoplankton compartment and related environmental parameters. A high frequency and/or high resolution approach, through the use of semi-automated flow cytometry, allowed us to reduce this loss of information and to better characterize the phytoplankton spatial and temporal variability in coastal water of the eastern English Channel.Three approaches were applied, leading to the ollowing results : (i) A high frequency study, performing one analysis every 10 minutes, which revealed a strong phytoplankton variability at the regional scale, with community assemblages that were not governed by hydrology ; (ii) A seasonal monitoring of the whole phytoplankton size-spectrum, which revealed the seasonal successions and the main factors governing them : nutrient concentrations and the daily light level which structured the transition of most phytoplankton groups ; (iii) A three-year follow-up at a coastal station, which made it possible to relate the traits-based characterization of each functional phytoplankton group to the environmental conditions, in order to better understand phytoplankton community assembly in response to environmental variability. The results have revealed a functional differentiation mainly due to the use of resources and the growth strategies, both of them driven by a resource gradient. This study confirms the importance of the "mass ration hypothesis", which predicts that the dominant life traits of the most abundant species, would be the main driver of the key ecosystem processes.

Les Hydrocarbures Aromatiques polycycliques (HAP) sont des polluants organiques persistants, dont la faible disponibilité dans les sols historiquement contaminés limite leur biodégradation. La capacité des plantes à favoriser l’élimination de ces polluants par l’action des microorganismes associés à leur rhizosphère a été montrée (rhizodégradation). Toutefois les résultats sont variables, suggérant la variabilité spatio-temporelle des processus. Des études à différentes échelles de temps et d’espace, utilisant des microcosmes et des dispositifs in situ ont été menées pour préciser ces phénomènes. L’étude de la variabilité spatiale des HAP et de la diversité bactérienne a été menée au sein de deux rhizosphères contrastées (ray-grass et luzerne), à l’échelle centimétrique après 37 jours de culture sur un sol de friche industrielle. Les résultats ont montré une spatialisation de la teneur en sucre et du pH, de la diversité bactérienne et de l’abondance microbienne, spécifique de l’espèce végétale, mais sans structuration de la teneur en HAP. L’étude de la variabilité temporelle de ces processus a révélé la dissipation en 6 jours des polluants biodisponibles ainsi qu’un effet positif des plantes par rapport au sol nu sur la dissipation des HAP et sur l’expression des gènes de HAP-dioxygénase. Une étude à plus long terme (6 ans) et in situ a montré que le couvert végétal ralentit la dissipation des HAP et influencent fortement la diversité microbienne, tout comme certains paramètres édaphiques. L’ensemble de ces résultats montre l’importance de la biodisponibilité des HAP qui conditionne leur dissipation, et de la dynamique des communautés microbiennes dans la rhizosphère / Polycyclic Aromatic Hydrocarbons (PAH) are persistent organic pollutants in soil, whose degradation in aged-contaminated soil is limited by their low bioavailability. The ability of plants to promote pollutant dissipation through the action of rhizosphere microorganisms has been shown (rhizodegradation). However contrasted results were obtained suggesting spatio-temporal variability of processes. Different experiments, with different time and space scales, using microcosm and field trials were achieved to precise phenomena. Study of spatial variability of PAH and bacterial diversity were done in two-contrasted rhizospheres (ryegrass and alfalfa) at centimeter scale after 37 days of plant growth, on a wasteland aged contaminated soil Results showed spatial structuration of sugar content, pH, bacterial diversity and microbial density, depending on plant species, but no vertical gradient was observed for PAH concentration. Study of temporal variability of processes showed dissipation of bioavailable fraction of pollutant in just 6 days and in comparison with bare soil, a positive impact of plant was shown on PAH dissipation and on expression of PAH dioxygenase genes. A long-term study (over 6 years) in a field trial revealed that plant cover slowed down PAH dissipation and impacted bacterial and fungal diversity as edaphic parameters. All these results underlined the importance of PAH bioavailability for the dissipation process and of spatio-temporal dynamic of microbial community, in the rhizosphere

Usualmente la producción de sedimentos en suspensión (Qss) de un río es calculada utilizando datos de caudales medios diarios o mensuales. Considerando que la mayor Qss ocurre durante los eventos de lluvias y también que los caudales medios no son capaces de representar adecuadamente los máximos caudales, principalmente en zonas de alta variabilidad climática, la forma usual de cálculo de Qss puede subestimar esta producción. En este sentido, esta investigación buscó analizar la influencia de la variabilidad temporal de los datos de caudales en el cálculo de la producción de sedimentos. Adicionalmente fue analizada el uso de diferentes tipos de curvas de sedimentos: (i) para todo el periodo de estudio, (ii) por años hidrológicos y (iii) asociación por épocas características (húmedas, semi-húmedas y secas). El estudio fue realizado en la subcuenca del río Torata, ubicada en una zona semiárida al sur del Perú, entre 2100 y 5200 m de altitud con pendiente promedio de 21.0% y alta variabilidad climática, en especial la precipitación que se ve reflejado en los caudales, ya que en un lapso de horas puede variar de 4 a 34 m3/s. El error entre la descarga prevista y estimada para el periodo de estudio (2001-2012) utilizando los diferentes tipos de curvas fue (i) -65.85%, (ii) -15.36% y (iii) -8.74%, presentando mejora en el coeficiente de eficiencia de Nash-Sutcliffe de 0.248 para 0.500. Los resultados mostraron que la diferencia entre la descarga de sedimentos en suspensión total para el periodo calculado con caudales medias mensuales y diarias fue de -92% y -62%, ambos en comparación de producción para valores medios horarios. También fue constatado que el 99.7% de la producción de sedimentos ocurre en temporada de lluvias, inclusive, un único evento de lluvia llegó a producir 80% de la producción anual. Los resultados de esta investigación ponen en manifiesto la importancia de utilizar registros de caudales con escalas pequeñas de tiempo (minutos, horas), que puedan representar la alta variabilidad de los caudales característicos de zonas semiáridas. / The usual methods that calculate the suspended sediment flux (Qss) of rivers employ discharge mean values daily or monthly. As most of the sediments are transported during overflow events and a mean value smooths the flood peak discharge, mainly in high climatic variability areas, the usual method to evaluate the Qss might underestimate the production of river sediments. This paper reports on an analysis of the gauge influence of temporal variability on the sediment yield estimation. Additionally, the use of different types of sediment rate curves was analyzed for (i) the whole time-series data, (ii) per hydrological year, and (iii) per hydrological pattern characterization (flood, intermediary and drought). A study case was conducted in the Torata river sub-catchment, a Peruvian semi-arid area located between altitudes of 2100 and 5200 meters and whose average slope is 21%. The high climatic variability is expressed by the huge river flow amplitude, which ranges from 4 to 34 m3/s in a few hours. The errors for the sediment yield from 2001 to 2012 estimated by the different sediment rating curves were (i) -65,85%, (ii) -15,36% and (iii) -8,74%, with a 0,248 to 0,500 Nash-Sutcliffe efficiency coefficient improvement. The differences between the sediment yield in total suspension for the period calculated monthly and daily were -92% y and -62%, respectively, in comparison with the production for hourly average values. Results show that 99,7% of the sediment are produced during the flood season and a single overflow event could represent 80% of the annual sediment discharge flow. This research highlights the importance of collecting and using discharge data of a short time interval (minutes or hours) to compute and represent the overflow peaks typical of semiarid regions.

Accelerating rates of change in ecosystems globally heighten the need for improved predictions of future ecological conditions. Freshwater lakes and reservoirs, which provide numerous ecosystem services, are particularly threatened by global change stressors and have already exhibited substantial changes to their physical, chemical, and biological functioning. Thus, to provide useful predictive tools for managing freshwater resources in the face of global change, we must improve our ability to build, apply, and communicate understanding of lake and reservoir ecosystem dynamics. To address this, I first built ecosystem understanding by conducting multiple whole-ecosystem surveys to quantify the spatial and temporal variability of biogeochemistry in two reservoirs over a year. We found that temporal heterogeneity was higher than spatial heterogeneity for most biogeochemical variables, with the stream-reservoir interface as a consistent hotspot of biogeochemical processing. Second, I applied ecosystem understanding by producing ecological forecasts of physical (water temperature), chemical (dissolved oxygen), and biological (chlorophyll-a) variables across three waterbodies using diverse modeling methods. I developed daily, weekly, and fortnightly forecasts of chlorophyll-a at two drinking water reservoirs using a Bayesian linear model, and found process uncertainty dominated total forecast uncertainty. Additionally, I produced forecasts of water temperature and dissolved oxygen in an oligotrophic lake using a hydrodynamic-ecosystem model and found that water temperature was more predictable than oxygen despite variable performance over depth and between years. Across these two forecasting studies, forecast skill relative to a null model varied among water quality metrics: water temperature forecasts outperformed the null model up to 11 days ahead, oxygen forecasts outperformed the null model up to 2 days ahead, and chlorophyll-a forecasts outperformed the null model up to 14 days ahead. Third, to communicate forecasts for decision-making, I developed an educational module for undergraduate ecology students which taught important concepts on visualization and decision science. Following completion of the module, students' ability to identify methods for uncertainty communication increased significantly, as well as their understanding of the benefits of ecological forecasting. Overall, my dissertation provides insight into how reservoirs function in global biogeochemical cycles, the predictability of multiple water quality variables, and deepens our understanding of how to communicate ecosystem science for improved management and protection of ecosystems. / Doctor of Philosophy / Human activities such as changing land use and climate have altered ecosystems around the world. As a result, many ecosystems no longer exhibit the same patterns from year to year as they have in the past, motivating the need for new tools to predict their future conditions. Among all ecosystems, freshwater lakes and reservoirs have been especially vulnerable due to human activities, threatening the critical services they provide to society, including drinking water and food, opportunities for recreational and cultural activities, and flood protection. Thus, because freshwater ecosystems are rapidly changing, forecasts of important water quality variables are needed. However, in order to use these forecasts effectively, a better understanding of how lakes and reservoirs change over space and time is needed, in addition to thoughtful communication of scientific findings for users. In my dissertation, I first addressed these needs by monitoring two reservoirs to examine how water quality varies over time and space. I found that water quality was more different over time (i.e., seasons) than over space (i.e., from one location to another within the reservoir). Second, I made ecological forecasts of water quality variables over space and time at different lakes. I forecasted phytoplankton levels in two drinking water reservoirs using a relatively simple model and water temperature and dissolved oxygen in a large clear-water lake using a more complex model. Comparing across forecasts in the three waterbodies, I found that my temperature forecasts provided valuable information above a baseline model up to 11 days ahead, oxygen forecasts up to 2 days ahead, and phytoplankton forecasts up to 14 days ahead. Third, because forecasts must be communicated effectively to be used as decision-making tools, I designed an educational module to teach forecast visualization and decision-making concepts. I found that students who completed the module better understood the benefits of forecasting for decision-making, and identified more ways to communicate forecasts after they completed the module. Overall, my dissertation shows the importance of measuring water quality over time and space to develop lake and reservoir forecasts, and demonstrates how forecast communication can help build students' understanding of the importance of forecasts for protecting and managing ecosystems.

<p>Fresh groundwater quality and availability in coastal areas is affected by seawater intrusion into coastal aquifers, and coastal water quality and ecosystem status may be significantly affected by groundwater pollutants that are transported into coastal waters by submarine groundwater dis-charge (SGD). This thesis uses an overall regional perspective for investigating: i) seawater intru-sion and its possible control in sustainable coastal groundwater management; ii) SGD and its relevant quantification as one interacting part among the diverse main regional pathways of freshwater and tracer/pollutant inputs from land to sea; and iii) the integrated system functioning of both i) and ii) as main components of the same coastal groundwater system.</p><p>Results show that intensive pumping rates may be maintained for a long time before major re-gional seawater intrusion problems are recognized by too high salinities in pumped groundwater. After such late recognition, pumping wells are no longer useful and a common strategy of mov-ing groundwater pumping further upstream from the coast only increases the extent of the salt-water intrusion zone into the aquifer. An alternative strategy may be to control seawater intrusion through artificial groundwater recharge, for instance by sufficiently treated wastewater, which may considerably reduce long-term trends of salinity increase in pumped groundwater, even for small artificial recharge rates compared to pumping rates. In general, account for natural spatial-temporal variability and randomness may be essential for relevant prediction of groundwater dynamics for management purposes. Spatial and temporal randomness effects, however, may not be additive, but rather largely overlapping, with either spatial or temporal randomness being the dominating part that must be accounted for in predictive groundwater dynamics calculations. Aquifer depth is identified as an important control parameter in this context, yielding much greater temporal randomness effects in shallow than in deep aquifers.</p><p>Combined simulation results suggest a simple, approximately linear regional relationship between total SGD and its hydrologically determined freshwater component. Tidal oscillation may signifi-cantly affect such linear dependence of steady-state SGD, but primarily for low SGD conditions. High SGD appears to depend mainly on a dominant freshwater component, which effectively counteracts density-driven flow of seawater into the aquifer and thus decreases also effects of sea-level oscillation on the seawater component of total SGD. Comparative analysis between different SGD estimation methods in different reported high-SGD regions of the world indicates possible anomalously large regional SGD estimation from tracer concentrations in coastal waters, by confusing different main pathways of groundwater flow and pollutant inputs to the sea.</p>

Freshwater bodies such as lakes and streams release the greenhouse gases methane (CH4) and carbon dioxide (CO2) into the atmosphere. Global freshwater CH4 and CO2 emissions have been estimated to be of a similar magnitude to the global land or ocean carbon sink, and are thus significant components of global carbon budgets. However, the data supporting global estimates frequently lacks information regarding spatial and temporal variability and are thus highly inaccurate. In this thesis, detailed studies of the spatio-temporal variability of CH4 and CO2 fluxes were conducted in the open water areas of lakes and streams within a whole catchment in Sweden. One aim was also to evaluate the importance of spatio-temporal variability in lake and stream fluxes when making whole catchment aquatic or large scale assessments. Apart from the expected large spatio-temporal variability in lake fluxes, interactions between spatial and temporal variability in CH4 fluxes were found. Shallow lakes and shallow areas of lakes were observed to emit more CH4 as compared to their deeper counterparts. This spatial variability interacted with the temporal variability driven by an exponential temperature response of the fluxes, which meant that shallow waters were more sensitive to warming than deeper ones. Such interactions may be important for climate feedbacks. Surface water CO2 in lakes showed significant spatio-temporal variability and, when considering variability in both space and time, CO2 fluxes were largely controlled by concentrations, rather than gas transfer velocities. Stream fluxes were also highly variable in space and time and in particular, stream CH4 fluxes were surprisingly large and more variable than CO2 fluxes. Fluxes were large from stream areas with steep slopes and periods of high discharge which occupied a small fraction of the total stream area and the total measurement period, respectively, and a failure to account for these spatially distinct or episodic high fluxes could lead to underestimates. The total aquatic fluxes from the whole catchment were estimated by combining the measurements in open waters of lakes and streams. Using our data, recommendations on improved study designs for representative measurements in lakes and streams were provided for future studies. Thus, this thesis presents findings relating to flux regulation in lakes and streams, and urges forthcoming studies to better consider spatio-temporal variability so as to achieve unbiased large-scale estimates. / Sötvatten som sjöar och vattendrag är källor till växthusgaserna metan (CH4) och koldioxid (CO2) i atmosfären. De globala utsläppen av CH4 och CO2 från sötvatten har uppskattats vara av samma storleksordning som den globala land- eller havskolsänkan och är därmed viktiga delar av jordens växthusgasbudget. De globala uppskattningarna saknar ofta information om variation i tid och rum och är därmed mycket osäkra. Denna avhandling behandlar hur CH4- och CO2-flöden från öppet vatten i sjöar och vattendrag i ett avrinningsområde varierar rumsligt och tidsmässigt. Ett syfte var också att utvärdera betydelsen av dessa variationer när data extrapoleras för att göra storskaliga uppskattningar av växthusgasflöden från vattenmiljöer. Förutom de förväntade stora rumsliga och tidsmässiga variationerna i sjöars gasflöden identifierades interaktioner mellan rumsliga och tidsmässiga variation för CH4-flöden. Den rumsliga variabiliteten med högre CH4-flöden från grunda vatten interagerade med tidsvariationen, som i sin tur drevs av en exponentiell temperaturrespons av gasflödena. Det betyder att grunda vattenområden var mer känsliga för uppvärmning än djupare vatten och därmed att vattendjupet har betydelse för hur sjöars CH4-utsläpp påverkas av klimatet. Koncentrationer av CO2 i sjöars ytvatten uppvisade också en betydande rumslig och tidsmässig variation som tillsammans visar att CO2-flöden över längre perioder till stor del styrs av koncentrationer snarare än av gasutbyteshastigheter. Vattendragens gasflöden varierade också mycket i tid och rum. Detta gällde i synnerhet CH4-flödena vilka var förvånansvärt stora och mer varierande än CO2-flödena. Gasflödena var höga från områden i vattendrag med högre lutning och då det var höga vattenflöden, trots att dessa områden och tidsperioder utgjorde en bråkdel av den totala arean och mätperioden. Att inte räkna med dessa gasflöden från bäcksektioner med höga vattenhastigheter eller korta perioder med höga flöden, leder till underskattningar. De totala CH4- och CO2-flödena från öppet vatten i hela avrinningsområdet uppskattades genom att kombinera mätningar i sjöar och vattendrag. Denna avhandling visar att rumslig och tidsmässig variabilitet har stor betydelse, och den ger information om hur denna variation kan beaktas för bättre framtida mätningar och storskaliga uppskattningar av växthusgasflöden från sjöar och vattendrag.

Cette thèse traite de la variabilité temporelle intrinsèque de l'éclairement solaire reçu au sol. Les échelles caractéristiques de variabilité sont mises en évidence par l'analyse de longues séries temporelles de moyennes journalières de l'éclairement, pour différents endroits du monde, issues de mesures pyranométriques au sol, d'estimations satellitaires ou de réanalyses météorologiques .Compte-tenu de la nature non linéaire et non stationnaire des données, la transformée adaptative de Hilbert-Huang est utilisée comme outil d'analyse pour tenir compte de la diversité de ces échelles temporelles. On montre ainsi la nature variable des échelles caractéristiques et de leur intensité, ainsi que leur dépendance vis-à-vis du climat.L'application d'une technique adaptative de ré-échantillonnage fractionnaire montre la juxtaposition d'une composante déterministe et d'une stochastique. Pour tous les jeux de données, le cycle annuel déterministe représente la plus grande partie de la variabilité. Toutes les séries temporelle contiennent une composante de variabilité stochastique à haute fréquence, qui est modulée en amplitude par le cycle annuel.L'approche permet également d'évaluer, échelle par échelle, les performances des estimations satellitaires ou issues de ré-analyses par comparaison avec des mesures pyranométriques au sol. Une étude de cas confirme que les estimations satellitaires surpassent les ré-analyses à toutes les échelles temporelles. / The center of focus for this PhD thesis is the intrinsic temporal variability of the surface solar irradiance (SSI). The characteristic time-scales of variability are revealed by analysing long-term time-series of daily means of SSI, such as ground measurements, satellite estimates, or radiation products from global atmospheric re-analyses, for different geographical locations around the world.To account for the wide range of the time-scales of variability, and given the non-linear and non-stationary nature of the data, the adaptive, data-driven Hilbert-Huang Transform is employed as an analysis tool. The time-varying nature of the characteristic time-scales of variability, along with variations in intensity, are thus revealed.An adaptive fractional re-sampling technique is used to discriminate between the deterministic and the stochastic variability constituents. For all datasets, the deterministic yearly cycle is found to account for the largest part of variability. Furthermore, all time-series are found to contain a high-frequency stochastic variability component, that exhibit cross-scale amplitude modulation by the yearly cycle.A refinement to existing methods for assessing the fitness for use of surrogate SSI products in lieu of ground measurements is also proposed. A case study confirms that satellite estimates outperform re-analyses across all time-scales.