Nutrients and particulate matter dynamics - exchanges between a COAstal LAgoon and the adjacent ocean through a multiple inlet system: the case of Ria Formosa, south of Portugal - COALA

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Qual a importância das trocas entre a Ria Formosa e o oceano adjacente para a produtividade biológica destes sistemas?

Publication . Cravo, Alexandra; Jacob, J.

A Ria Formosa é a lagoa costeira mais importante do sul de Portugal, com grande influência nas trocas de água e de matéria com o oceano adjacente, as quais controlam a produtividade biológica destes ecossistemas intimamente ligados. Neste capítulo são apresentadas as características geomorfológicas da Ria Formosa e as características dinâmicas que a tornam um sistema bastante produtivo e peculiar, com forte impacto no oceano adjacente. São ainda apresentadas, pela primeira vez, as trocas através das três barras do setor oeste da Ria Formosa, em condições de maior produtividade biológica, típicas de Primavera, evidenciando a importância da interligação entre estes dois sistemas, particularmente num período sob afloramento costeiro.

2021Book part

Open Access

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 forces

Publication . 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.

2019-02Journal article

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Water exchanges between a multi-inlet lagoon and the ocean: the role of forcing mechanisms

Publication . Fabião, João Pedro Farinha; Rodrigues, Marta Filipa Gomes; Fortunato, André Bustorff; Jacob, J.; Francisco Cravo, Alexandra Maria

Understanding the influence of the main drivers controlling the circulation and the transport in coastal lagoons is a necessary step towards the description of the dynamics of their ecosystems. Thus, the influence of the main physical drivers on the water exchanges in a multi-inlet barrier island (western sector of the Ria Formosa coastal lagoon, Portugal) was investigated. Several scenarios of tide, wind, bathymetry and point source discharges were simulated using a three-dimensional circulation model and a particle-tracking model. The circulation is adequately reproduced by the hydrodynamic model, with root mean square errors of about 5-8 cm for the water levels and 5-10 cm/s for the cross-sectional averaged velocities in the western inlets and main channels. Wind has a negligible effect on the modelled water levels and cross-sectional velocities, with differences smaller than 1 % between the simulations with and without wind. However, results show that wind influences significantly the transport by affecting the residual circulation, with distinct effects depending on the wind direction. Upwelling favourable winds (with west component) increase the landward transport through the Faro-Olho inlet and promote a larger dispersion of the water-borne material inside the lagoon. The residual circulation between the three inlets of the western sector of the lagoon is also significantly affected by the bathymetry. Results show a decrease of about 50 % of the tidal prism of the Anco inlet between 2002 and 2011, which reduces its capacity to export waterborne material to the adjacent coastal area and increases the residence times in some areas of the lagoon, with potentially adverse effects on the ecosystems' health. The dispersion of potential contaminants from point sources inside the lagoon to the coastal area depends on the combined effect of the tidal phase and amplitude and the location of the source. Mean residence times for the discharges from the wastewater treatment plants of the western sector ranged from 7 to 18 days. These findings improve the understanding of the influence of the physical forcings in the circulation and transport dynamics of multi-inlet coastal systems.

2016-02Journal article

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