Abstract
The present study aims to research the physico-chemical processes in two under-researched coastal systems located on the west and south Portuguese coast—Mira Estuary and Ria de Alvor—through the development and exploitation of dedicated coupled physical and water quality models. Both systems are highly dynamic, supporting a wide range of biological diversity; however, they are characterized by distinct environmental and oceanographic conditions, enhancing the importance of a comparative approach. In this context, the Delft3D modeling suite was implemented and successfully calibrated and validated for both systems, accurately reproducing their hydrodynamic, hydrographic, and chemical features. A broad characterization of Mira Estuary and Ria de Alvor was carried out. Results show that the tidal wave interacts differently with the different geomorphology of each estuary. The tidal wave amplitude decreases as it propagates upstream for both estuaries; however, the magnitude for Ria de Alvor is higher. A flood tidal dominance was found for Mira Estuary, allowing the transport of well-oxygenated water into the estuary, contributing to high residence times in the middle estuary and therefore to poor dissolved oxygen (DO) replenishment. Ria de Alvor shifts from ebb dominance at the central area to flood dominance upstream with low residence times, allowing an effective exchange of water properties. Results also reveal that the water temperature is the dominant driver of seasonal dissolved oxygen variations in both estuaries, with the lowest levels occurring during the late summer months when the water temperature is highest. In addition, pH is influenced by biological activity and freshwater inflow.
Highlights
Coastal systems are very important interface areas between land and open sea, supporting productive ecosystems
In situ monitoring was collected in the frame of this study in each estuary in order to obtain the data required for model calibration and validation purposes
The results for Mira Estuary and Ria de Alvor are portrayed in Figures 2 and 3, respectively, considering hydrodynamic (sea surface elevation (SSE) and current velocity—u and v components), salt and heat and water quality (DO and pH) parameters
Summary
Coastal systems are very important interface areas between land and open sea, supporting productive ecosystems. There is a growing interest in studying estuarine systems, especially their functioning and evolution, using novel dedicated coupled physical–biological models [3,4] These models constitute valuable tools that complement observational gaps and provide continuous estimates and forecasts of the water state. The study of the smallest estuarine systems has been neglected, despite its extreme importance as valuable local resources, such as Mira Estuary and Ria de Alvor. These coastal systems are located on the Portuguese west (Alentejo) and south (Algarve) coasts, respectively, and they are subjected to different environmental and oceanographic forcing conditions.
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