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Spatio-temporal variability of phytoplankton in the Tagus Estuary : implications to water quality
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Estuaries are systems of ecological importance that also suffer from several anthropogenic pressures. Phytoplankton is considered an important water quality indicator due to its rapid response to variations in the environment. However, to adequately assess phytoplankton in estuaries it is important to understand how phytoplankton reacts to estuarine variability. Thus, the main aim of the present doctoral thesis is to improve the knowledge of the effects of temporal and spatial variations of the Tagus Estuary environment over the water quality metrics and to predict how it will respond in the future, under climate change scenarios. Thus, this study has the following objectives: i) understand the tidal effect over the estuarine physicochemical conditions and phytoplankton community; ii) assess the tidal effect over the water quality metrics; iii) understand the spatial and seasonal variability of physicochemical conditions and phytoplankton in the Tagus Estuary, as well as the effect of such variations over the Water Framework Directive (WFD) water quality metrics and iv) simulate the effects of increased outfall discharges and climate change over the Tagus Estuary physicochemical parameters and phytoplankton community and its effects on the WFD metrics. The results demonstrate that chlorophyll-a concentrations were higher during spring tides along with higher particulate matter concentrations. The low-neap tide was the most appropriate tidal condition to observe the worst-case scenario, mainly in the location more influenced by outfalls. In general, chlorophyll-a concentrations were higher during the Summer and Spring accompanied with higher suspended matter concentrations while nutrients concentrations were higher during the winter. Both, the simulations of sea level rise and reduction of river discharge led to a decrease of chlorophyll-a and nutrients concentrations while increasing salinity. In conclusion, the phytoplankton community of the Tagus Estuary is influenced by both temporal and spatial drivers, with a decrease in nutrients and chlorophyll-a concentrations expected in the future.
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Fitoplâncton variabilidade espacial e temporal Indicadores de qualidade da água Diretiva Quadro da Água alterações climáticas Phytoplankton drivers of variability water quality classifications Water Framework Directive climate change