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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.
- Impacts of decommissioning and upgrading urban wastewater treatment plants on the water quality in a shellfish farming coastal lagoon (Ria Formosa, South Portugal)Publication . Jacob, J.; Correia, Cátia; Torres, Ana Flor; Xufre, Gustavo; Matos, André Filipe; Ferreira, Cristina; Reis, Margarida; Caetano, Sandra; Freitas, Carla; Barbosa, Ana B.; Cravo, AlexandraRia Formosa is a productive coastal lagoon, located on the south coast of Portugal, and represents the largest national producer of shellfish bivalves (ca. 90% production). This ecosystem is subjected to various anthropogenic pressures, including the discharge of urban wastewater treatment plants (UWWTP), which impacts the lagoon water quality. This study aimed to assess the impact of alterations in the functioning of two UWWTP on the water quality of Ria Formosa, based on chemical variables, phytoplankton composition ( including potential harmful species) and faecal contamination. During the period September 2018 - October 2019, water sampling was conducted along dominant longitudinal gradients of the effluent dispersion from the discharge point (1-2 km), for two sites: a decommissioned (OP) and a modified (FO) UWWTP. After modification, the later started receiving a higher influent volume (ca. 40%), under an innovative technology system (biological treatment in aerobic granular sludge). Based on chemical water quality variables, phytoplankton and indicators of faecal contamination, a significant improvement along the longitudinal gradient from the discharge point was observed after OP decommissioning. This improvement was fast, being detected two months after decommissioning, positively affecting areas used as shellfish farming grounds. However, distribution patterns of bacteriological indicators and regular shellfish harvesting interdictions suggested an alternative source of faecal contamination after OP decommissioning. At FO, both chemical variables and bacteriological indicators of faecal contamination revealed a slower improvement, only six-months after the UWWTP alteration. Before that, increased and highly variable ammonium, chlorophyll a concentration, phytoplankton abundances and Escherichia coli densities, revealed an unstable phase. Overall, a lower water quality at FO in respect to OP reflected not only a higher effluent volume but also more restricted water circulation for the former.
- Nutrients and chlorophyll-a exchanges through an inlet of the Ria Formosa Lagoon, SW Iberia during the productive season - Unravelling the role of the driving forcesPublication . Cravo, Alexandra; Cardeira, Sara; Pereira, Catarina; Rosa, Monica; Alcantara, Pedro; Madureira, Miguel; Rita, Filomena; Correia, Cátia; Rosa, Alexandra; Jacob, J.Despite the advances and increase of observations of physical and chemical processes to better understand thefunctioning of coastal environments, a large gap still exists in quantifying exchanges and interactions betweenadjacent coastal systems. It is important to bear in mind that the dynamics and mass exchanges depend on thevariability of the driving mechanisms and respond to several time scales (tidal, seasonal and inter-annual). Thegeneral objective of this work was to unravel the role of the driving forces on the nutrients and chlorophyll-aexchanges at the Ancão inlet of Ria Formosa lagoon during the most productive season - spring. This is thesmallest inlet of the western system, the closest to continental interface and the one where migratory patterns areevident. So, the changes along time could be more evident there than at the other two inlets of the westernsector. Ancão inlet will serve as a reference to compare the mass budgets exchanged with the ocean with theother two inlets. Specifically, this work intends to: i) better understand the behaviour of this inlet; ii) its role inthe mass exchanges; and iii) its interplay with phytoplankton productivity during the peak season. In thiscontext, the transport of water, nutrients and chlorophyll-a(proxy of phytoplankton density) were estimatedacross the Ancão inlet section during the spring season. Surveys were conducted under extreme fortnightly tidalconditions during 2007, 2009 and 2012, covering different hydrodynamic, meteorological and environmentalconditions. To estimate the mass transport,field velocities, nutrients and chlorophyll-aconcentrations weremeasured concurrently along its cross section. Results show that although the hydrodynamic and morphologicchanges recorded at this inlet provoked a loss of hydraulic efficiency apparently these did not markedly affectthe mass exchanges during the spring productive season. Globally, the contribution and intensity of the me-teorological/physical, chemical and biological drivers superimposed those affected by tides, reflected in thedifferences between thefive surveys conducted. Upwelling was frequent during the spring season and played akey role on the exchanges and mass transport through the Ancão inlet. Data also show that nutrients behaveddissimilarly; silicate was consistently exported, nitrate mostly imported, dependent on the intensity of upwellingand biological consumption, while phosphate generally followed the direction of residual circulation.Chlorophyll-ashowed a general import except in both 2012 campaigns, when it was exported in small amounts(< 1 kg). Data support that during spring season, particularly in periods when upwelling is relevant, theavailability of nutrients on the coast will promote afterwards the growth of phytoplankton that enters andfertilizes the Ria Formosa, increasing its productivity. The estimated amounts are relative to the smallest inlet ofthe western sector of Ria Formosa. In consequence, it may be anticipated that through the other main inlets fromthis sector the exchanges are intensified and may enhance their contribution to the Ria Formosa fertilization.