Groundwater in upland floodplains has an important function in regulating river flows and controlling the coupling of hillslope runoff with rivers, with complex interaction between surface waters and groundwaters throughout floodplain width and depth. Heterogeneity is a key feature of upland floodplain hydrogeology and influences catchment water flows, but it is difficult to characterise and therefore is often simplified or overlooked. An upland floodplain and adjacent hillslope in the Eddleston catchment, southern Scotland (UK), has been studied through detailed three-dimensional geological characterisation, the monitoring of ten carefully sited piezometers, and analysis of locally collected rainfall and river data. Lateral aquifer heterogeneity produces different patterns of groundwater level fluctuation across the floodplain. Much of the aquifer is strongly hydraulically connected to the river, with rapid groundwater level rise and recession over hours. Near the floodplain edge, however, the aquifer is more strongly coupled with subsurface hillslope inflows, facilitated by highly permeable solifluction deposits in the hillslope–floodplain transition zone. Here, groundwater level rise is slower but high heads can be maintained for weeks, sometimes with artesian conditions, with important implications for drainage and infrastructure development. Vertical heterogeneity in floodplain aquifer properties, to depths of at least 12 m, can create local aquifer compartmentalisation with upward hydraulic gradients, influencing groundwater mixing and hydrogeochemical evolution. Understanding the geological processes controlling aquifer heterogeneity, which are common to formerly glaciated valleys across northern latitudes, provides key insights into the hydrogeology and wider hydrological behaviour of upland floodplains.

Stable isotopes (δ¹⁸O, δD), dissolved silica (DSi) concentration and major ion composition were used to indicate groundwater/surface-water interaction between the aquifers, the rivers and a lake in the high-latitude Lake Pyhäjärvi catchment in Finland. Significant differences were recorded in water chemistry between the groundwater and surface waters, especially in the stable isotope composition and DSi concentrations, which could thus be used as tracers. The baseline data on isotopic patterns and hydrogeochemistry in the hydrological cycle were provided by a 1-year monitoring survey in this snow-type catchment area. The proportions of groundwater in the rivers, the lake inshore area and in a groundwater abstraction plant were calculated using stable isotopes and DSi. Two inflowing rivers had distinct differences in their water chemistry. DSi has potential as a tracer in the river environment, whereas stable isotopes were more applicable in the lake environment. Locally, near the shoreline, the effect of discharging groundwater on the lake-water quality could clearly be observed. Furthermore, infiltration of the lake water into the aquifer could be observed near the pumping wells onshore. This infiltration presents a potential risk for the water quality of water supply (intake) wells. Frequent sampling is needed as part of the evaluation of the level of groundwater/surface-water interaction in snow-type catchments in order to estimate the magnitude of seasonal variation. In groundwater/surface-water interaction studies, spring thaw and high-precipitation events could be problematic, in terms of both sampling and interpreting results.

The "Metabolic Theory of Ecology (MTE) uses temperature as the environmental variable that predicted diversity patterns of ectothermic organisms. Specifically, the MTE predicts that the relationship between species richness (dependent variable) and the inverse of temperature (independent variable) has a slope ranging from -0.6 and -0.7. Thus, this study tested whether the pattern of species richness of freshwater fishes in Brazilian reservoirs fits of the MTE predictions. Besides temperature, other variables (potential evapotranpiration, actual evapotranspiration, precipitation, net primary productivity, elevation, age and area of reservoirs and b of EER - Energetic Equivalence Rule - slope of the relationship between body size and abundance of species) were used to test the MTE predictions. The MTE was tested using data from compilations (without control of the sampling effort) and sampled data (with standardized effort). For the latter data set all the MTE assumptions (ectothermic organisms, with high levels of taxonomic organization and whose body size and abundance do not vary spatially) were met. The tests were performed using OLS regressions and autoregressive models (SAR) and spatial filtering approach were used to minimize the effects of spatial autocorrelation when it was detected. To evaluate whether the lack of fit to the MTE predictions results from the violation of the spatial invariance assumption in abundance and species body size, it was added the slope's values of the b of EER as a predictor variable. The Akaike Information Criterion was used to select the best model and the spatial filters approach was used to minimize the autocorrelation when it was present. Partial regressions were used to evaluate the pure effect of the different components (local, regional, spatial/population) for the explanation of species richness. It was found that the species number increased toward the lower latitudes. The analyses for compiled data revealed consistency with the MTE predictions after removing the autocorrelation in the regression's residuals. For sampled data was not observed spatial autocorrelation in the regression residuals. However, the results were discordant with the MTE predictions, even adding the b of EER in model. For compiled data the variables temperature, precipitation and habitat age were retained in the best model, explaining 61.7% of the variation in the species richness after removing the spatial autocorrelation. Using the sampled data the same variables plus b EER were retained in the best model, which explained 90% of the variation in richness. Controlling the sampling effort and adding variables to the model originally proposed by the MTE, the slope of the relationship between species richness and temperature was consistent with the MTE predictions. The regional component effect (temperature and precipitation) contributed to explain the most variation of richness. We conclude that the MTE's failure in supporting empirical evidences should not be attributed to the assumptions violation and that the theory should consider the sampling effort control as an important condition to test the MTE prediction. The sampling effort control may reduce the problems of the spatial autocorrelation, besides generate parameters that modify quantitatively the results and qualitatively the interpretations. The relevant factors to the MTE's adjustment were the sampling effort control to obtain the specimens, no violation of assumptions and incorporating other variables in the model, which can vary substantially according to the taxonomic groups and habitats that occupy. | A "Teoria Metabólica da Ecologia" (MTE - Metabolic Theory of Ecology) usa a temperatura como variável ambiental preditora dos padrões de diversidade de organismos ectotérmicos. Especificamente, a MTE prediz que a relação entre riqueza (variável dependente) e temperatura (variável independente) apresenta um valor de inclinação de reta variando entre -0,6 e -0,7. Assim, este estudo testou se o padrão de riqueza de espécies de peixes de água doce em reservatórios brasileiros se ajusta às predições da MTE. Além da temperatura, outras variáveis (evapotransiração potencial, evapotranspiração atual, precipitação, produtividade primária líquida, elevação, idade e área dos reservatórios e b da EER (Energetic Equivalence Rule - inclinação da relação entre abundância e tamanho do corpo das espécies) foram usadas para testar as predições da MTE. Foi verificado se houve diferenças nos ajustes utilizando-se dados de riqueza provenientes de compilações (sem controle do esforço amostral) e amostragens (com controle do esforço amostral). Para este último conjunto de dados todos os pressupostos da MTE (organismos ectotérmicos; com altos níveis de organização taxonômica, cujo tamanho do corpo e abundância não variem espacialmente) foram atendidos. Os testes foram feitos utilizando-se regressões OLS, sendo que modelos autorregressivos (SAR) e abordagem de filtros espaciais foram utilizados para minimizar os efeitos da autocorrelação espacial quando esta foi detectada. Verificou-se também se a falta de ajuste dos dados à MTE é decorrente da violação do pressuposto da invariância espacial na abundância e tamanho do corpo das espécies acrescentando-se como preditor os valores do b da EER. O critério de informação de Akaike foi utilizado para selecionar o melhor modelo e regressões parciais utilizadas para avaliar o puro efeito dos diferentes componentes (local, regional, espacial/populacional) para a explicação da riqueza. No geral, verificou-se que o número de espécies aumentou em direção às menores latitudes. As análises para dados compilados revelaram compatibilidade com as predições da MTE após a remoção dos efeitos da autocorrelação espacial nos resíduos da regressão. Para dados amostrados não foi observada autocorrelação nos resíduos da regressão e os resultados mostraram-se bastante discordantes das predições da MTE, mesmo acrescentando-se o b da EER no modelo. Para dados compilados, as variáveis temperatura, precipitação e idade dos reservatórios foram constituintes do melhor modelo e explicaram 61,7% da variação na riqueza após a remoção da autocorrelação. As mesmas foram retidas para dados amostrados adicionando-se o b da EER, as quais explicaram 90% da variação da riqueza. Padronizando o esforço amostral e adicionando variáveis ao modelo originalmente proposto pela MTE, o valor da inclinação da relação entre a riqueza de espécies e a temperatura foi compatível com as predições da teoria. O puro efeito do componente regional (temperatura e precipitação) foi responsável pela maior porcentagem de explicação da riqueza. Foi possível concluir que a falha da MTE em suportar evidências empíricas não pode ser atribuída à violação dos pressupostos e que a teoria deveria assumir como condição importante o controle do esforço amostral, pois além de reduzir problemas de autocorrelação nos resíduos da regressão pode gerar parâmetros que modificam quantitativamente os resultados e qualitativamente as interpretações. Além disso, concluiu-se que os fatores relevantes para o ajuste da MTE foram o controle do esforço amostral, a não violação de pressupostos e a incorporação de outras variáveis no modelo, as quais podem variar de acordo com os grupos estudados e hábitats que ocupam. | PhD

Microorganisms play a key role in aquatic biogeochemical cycles and in the flow of matter and energy through planktonic food webs. The first two chapters of this thesis aimed to investigate the main factors affecting bacterial abundances in tropical freshwater environments, due to an apparent paradox which emerged from previous studies: despite the higher bacterial production in the tropics, the bacterial abundance found in those regions is lower, compared to temperate environments. This fact raised the hypothesis that bacterial abundance could be controlled by heterotrophic flagellates in the lower latitudes. By analyzing a large data set, we showed that both bacterial and heterotrophic flagellate abundances are consistently lower in tropical when compared to temperate regions, resulting in a similar coupling between those communities. A stronger top-down control on both microbial communities exerted by ciliates and cladocerans, may explain those patterns. The experimental approach allowed us to demonstrate that protists, mainly ciliates, are likely the main responsible for bacterial loss in a tropical lake and that predation pressure also influences bacterial community size-structure. In the third chapter, we aimed to comprehend the role of temporal and spatial scales in structuring the planktonic ciliate communities from Neotropical floodplains, through a metacommunity approach. Contrasting results have been reported in the literature: while some authors advocated that microorganisms have a cosmopolitan distribution, others argued that they displayed biogeographic patters similar to those found for larger sized organisms. Taking into account both spatial and temporal scales, our analysis allowed us to demonstrate a clear influence of the temporal variation in structuring the planktonic ciliate communities, and with the analysis of a great spatial extent, it was possible to verify that biogeographic patterns also occur for those small-sized organisms. | Os microrganismos são fundamentais nos ciclos biogeoquímicos e participam ativamente do fluxo de matéria e energia através das teias alimentares planctônicas. Investigou-se os principais fatores que afetam a abundância bacteriana em ambientes de água doce tropicais, uma vez que um aparente paradoxo surgiu de estudos prévios: apesar da maior produção bacteriana encontrada em regiões tropicais, quando comparada à das regiões temperadas, menores abundâncias bacterianas eram registradas. Esse fato levantou a hipótese de que a abundância bacteriana seria controlada por flagelados heterotróficos nos trópicos. Através da análise da base de dados de diversos ambientes tropicais, constatamos que tanto a abundância bacteriana quanto a de flagelados heterotróficos é consistentemente menor em regiões tropicais quando comparada à das regiões temperadas, resultando em um acoplamento similar entre essas comunidades. Um maior controle top-down exercido sobre ambas as comunidades microbianas por ciliados e cladóceros, pode explicar os padrões encontrados. A abordagem experimental demonstrou que os protistas, principalmente os ciliados, são provavelmente os principais responsáveis pela perda bacteriana em uma lagoa tropical, e que a pressão de predação também influencia a estrutura de tamanho da comunidade bacteriana. Investigaram-se também, na estruturação da comunidade de ciliados planctônicos de planícies de inundação Neotropicais, as escalas temporais e espaciais, através da abordagem de metacomunidades. Estudos acerca desse tema mostraram resultados contraditórios: enquanto para alguns os microrganismos apresentavam uma natureza cosmopolita, para outros, padrões biogeográficos seriam semelhantes àqueles encontrados em macrorganismos. Análise da escala espaço-temporal indicou a influência da variação temporal na estruturação da comunidade de ciliados. Conforme a análise de uma grande extensão espacial foi possível verificar que padrões biogeográficos também ocorrem para organismos de pequeno tamanho. | PhD

Aquifers within the Pampa del Tamarugal Basin (Atacama Desert, northern Chile) are the sole source of water for the coastal city of Iquique and the economically important mining industry. Despite this, the regional groundwater system remains poorly understood. Although it is widely accepted that aquifer recharge originates as precipitation in the Altiplano and Andean Cordillera to the east, there remains debate on whether recharge is driven primarily by near-surface groundwater flow in response to periodic flood events or by basal groundwater flux through deep-seated basin fractures. In addressing this debate, the present study quantifies spatial and temporal variability in regional-scale groundwater flow paths at 20.5°S latitude by combining a two-dimensional model of groundwater and heat flow with field observations and δ¹⁸O isotope values in surface water and groundwater. Results suggest that both previously proposed aquifer recharge mechanisms are likely influencing aquifers within the Pampa del Tamarugal Basin; however, each mechanism is operating on different spatial and temporal scales. Storm-driven flood events in the Altiplano readily transmit groundwater to the eastern Pampa del Tamarugal Basin through near-surface groundwater flow on short time scales, e.g., 10⁰–10¹ years, but these effects are likely isolated to aquifers in the eastern third of the basin. In addition, this study illustrates a physical mechanism for groundwater originating in the eastern highlands to recharge aquifers and salars in the western Pampa del Tamarugal Basin over timescales of 10⁴–10⁵ years.

Stable isotopes of the water molecule (δ¹⁸O and δD) for groundwater, lake water, streams, and precipitation were coupled with physical flux measurements to investigate groundwater–lake interactions and to establish a water balance for a structurally complex lake. Georgetown Lake, a shallow high-latitude high-elevation lake, is located in southwestern Montana, USA. The lake is situated between two mountain ranges with highlands primarily to the east and south of the lake and a lower valley to the west. An annual water balance and (δ¹⁸O and δD) isotope balance were used to quantify annual groundwater inflows of 2.5 × 10⁷ m³/year and lake leakage outflows of 1.6 × 10⁷ m³/year. Roughly, 57% of total inflow to the lake is from groundwater, and 37% of total outflow at Georgetown Lake is groundwater. Stable isotopes of groundwater and springs around the lake and surrounding region show that the east side of the lake contains meteoric water recharged annually from higher mountain sources, and groundwater discharge to the lake occurs through this region. However, springs located in the lower western valley and some of the surrounding domestic wells west of the lake show isotopic enrichment indicative of strong to moderate evaporation similar to Georgetown Lake water. This indicates that some outflowing lake water recharges groundwater through the underlying west-dipping bedrock in the region.