A series of 25 Nimbus 7 coastal zone color scanner images obtained from July 1981 to September 1983 in Portuguese coastal waters was analyzed in order to study the space‐time distribution of phytoplankton pigment. In the images from winter and spring, the phytoplankton distributions showed no significant spatial patterns. During the upwelling season, from late June to October, several recurrent patterns were observed. Filaments of high pigment concentration extended zonally 200 km off the west coast of Portugal, north of Lisbon. Pigment‐rich plumes were observed south of capes along the west coast, south of Lisbon, and parallel to the south coast of Portugal. The location of the filaments and plumes coincided with topographic features such as submarine ridges. South of Lisbon the location of plumes was also related to coastal morphology. The temporal variability of the pigment patterns was compared with the wind‐induced offshore Ekman transport calculated from measurements made at two meteorological stations, located at Lisbon and Faro, on the south coast. A significant relationship was found: well‐developed phytoplankton structures were generally related to moderate or intense offshore transport, whereas the absence of plumes corresponded to either weak offshore transport or coastal convergence. For each of the three coastal areas in this study, scatter plots showed linear relationships between digital counts of phytoplankton concentration and sea surface temperature. The spatial variation of the temperature range decreased in time after the onset of an upwelling event. One cause of this variation could be the north‐south change in temperature of the upwelled Eastern North Atlantic Central Water along the Portuguese coast.

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The circulation in estuaries promotes the transport of organisms, nutrients, oxygen and sediments. Simultaneously, the mixture of fresh and salt water leads to variations of the physicochemical and biological components of the region. Therefore, it is important to further understand the hydrodynamic patterns of an estuary as one of the bases to understand the whole dynamic of these systems, ecologically important regions that must be preserved. However, little is known about the hydrodynamics of some estuarine systems. In order to bridge the knowledge gap about the Sado estuary, sampling was conducted with the purpose of evaluating some circulation patterns of the estuary and classifying it according to the stratification of the water column. The campaigns were conducted to collect monthly data on the intensity and direction of the currents, and on the temperature and salinity of the water column, between September 2018 and September 2019. The data indicated that water circulation in the Sado estuary, occurred through the two main navigation channels (North and South), according to the tidal regime. Both the temperature and the salinity were homogeneous along the water column, revealing little stratification. The analysis suggests possible hydrodynamic changes of the estuary in the past years.

To establish effective water quality monitoring strategies in estuaries, it is imperative to identify and understand the main drivers for the variation of water quality parameters. The tidal effect is an important factor of the daily and fortnightly variability in several estuaries. However, the extent of that influence on the different physicochemical and biological parameters is still overlooked in some estuarine systems, such as the Sado Estuary, a mesotidal estuary located on the west coast of Portugal. The main objective of this study was to determine how the water quality parameters of the Sado Estuary varied with the fortnightly and the semidiurnal tidal variation. To achieve this goal, sampling campaigns were conducted in May/18, Nov/18 and Jun/19, under neap and spring tidal conditions, with data collection over the tidal cycle. Results were observed to be significantly influenced by the tidal variation, in a large area of the estuary. Flood seemed to mitigate possible effects of nutrient enrichment in the water column. Additionally, significant differences were also observed when considering the different sampling stations. Temperature, Suspended Particulate Matter (SPM) and nutrients showed the highest values at low water. Lastly, the implications of the tidal variability in the evaluation of the water quality according to Water Framework Directive were also discussed, highlighting the importance of studying short-time scale variations and the worst-case scenario to ensure water quality is maintained. These findings are relevant for the implementation of regional management plans and to promote sustainable development.