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- Dissolved oxygen dynamics in Ria Formosa Lagoon (South Portugal) - A real time monitoring station observatoryPublication . Cravo, Alexandra; Rosa, Alexandra; Jacob, J.; Correia, CátiaDissolved oxygen (DO) is considered one of the most important environmental variables of water quality. This work aimed to provide, for the first time, insights regarding DO dynamics on a representative site of the productive Ria Formosa coastal lagoon, south Europe, using a real time monitoring station observatory (acquiring data every 15 min) deployed for a period of two and a half years. This comprehensive data set represents an added value contributing to a better understanding of the DO variability throughout analyzing semidiurnal, daily, fortnightly tidal cycles (spring tide vs. neap tide), seasonal and interannual periods. This observational station was able to capture distinct temporal signatures, including episodic upwelling and meteorological events advancing the knowledge about the functioning of Ria Formosa. DO was highly variable presenting an evident seasonal distribution with the maximum concentration in spring and the minimum in summer night periods. Critical values < 5 mg/L were recorded only in 3% of the global data set with negligible hypoxia events, showing infrequent DO stressful conditions in the study area. In addition, the disclosure of its did dynamics over long periods, provided by this data set, allows to determine the impact of biological activity upon the DO variability and related ecosystem metabolism behavior (autotrophic vs. heterotrophic), through the metric estimation of Net Ecosystem Metabolism (NEM). NEM in the study area revealed to be slightly heterotrophic along one year of observation, reflecting the median percentage of DO saturation (93%). The acquired data set is highly valuable and can contribute to Ria Formosa management and protection, which is imperative for building knowledge-based societies.
- Integrating physical and biogeochemical processes and oceanic exchanges at a coastal lagoon in Southern West EuropePublication . Cravo, Alexandra; Jacob, José; Rosa, Alexandra; Correia, CátiaCoastal lagoons are highly productive systems and the quantification of mass fluxes, which is of paramount importance for the sustainable management of these systems, remains poorly studied. In this context, a detailed study was conducted to better understand the exchanges between the productive coastal lagoon Ria Formosa (South-West Europe) and the ocean. The exchanges of water, nutrients, chlorophyll-a and suspended solids between the main inlets (Faro-Olhao inlet - BFO; Armona inlet - BAR; and Ancao inlet - BAN) and adjacent channels (Faro - CF and Olhao - CO) and the adjacent ocean were estimated along complete semidiurnal tidal cycles, under extreme fortnightly tidal ranges and different seasonal and environmental/oceanographic conditions. The net tidal prism was highest during spring tides. Among the three inlets, BFO was the most important in terms of exchange, followed by BAR and BAN. Net transport at BFO was lowest during the Summer campaign, although it exported material that fertilised the adjacent coast. The persistent net export of suspended solids and ammonium suggests the higher biological productivity of Ria Formosa compared to that found in coastal waters. In the Winter campaign, after a period of rainfall and increased land runoff, there was a remarkable export of matter, on which, ammonium and suspended particles exported can exceed 0.3 times and almost 0.9 times, respectively, those imported from coastal water. However, the import of phosphate and nitrate can be attributed to a weak coastal upwelling event, as well to low consumption and nitrification at this period of low temperature. During the Spring and Autumn campaigns, the Ria Formosa was fertilised either by upwelling events or due to rapid consumption of nutrients by phytoplankton in this shallow system. BFO and the other two inlets of the western sector of Ria Formosa are interconnected by CF and CO. The higher nutrient transport was recorded at CF, despite the highest nutrients concentrations was recorded at CO. The data show the strong link between physical and biogeochemical processes with meteorological/oceanographic factors. The study showed that associated biological processes are superimposed on the tidal effect in this system. Data from this study could be used as a reference, particularly important for management of Ria Formosa, a productive system where bivalves production depends deeply on water quality. In addition, the nutrient concentrations and mass exchanges resulting from the different processes can be used as a reference for other lagoon systems where shellfish production is practised.