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

• Published in: Journal of sea research Vol. 144; pp. 133 - 141
• Main Authors: Cravo, Alexandra, Cardeira, Sara, Pereira, Catarina, Rosa, Mónica, Alcântara, Pedro, Madureira, Miguel, Rita, Filomena, Correia, Cátia, Rosa, Alexandra, Jacob, José
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.02.2019; Elsevier BV
• Subjects: Ancão inlet; Biological fertilization; Chemical reactions; Chlorophyll; Chlorophyll a; Coastal environments; Dynamics; Environmental conditions; Exchanges; Exports; Fertilization; Hydrodynamics; Inlets; Inlets (topography); Inlets (waterways); Interactions; Mass transport; Mineral nutrients; Nutrient availability; Nutrients; Ocean circulation; Organic chemistry; Phosphates; Phytoplankton; Plankton; Polls & surveys; Productivity; Ria Formosa; Seasons; Silicates; Spring; Spring (season); Surveys; Tides; Transport; Upwelling; Mass transport; Nutrients; Chlorophyll-a; Exchanges; Ancão inlet; Ria Formosa
• ISSN: 1385-1101; 1873-1414
• DOI: 10.1016/j.seares.2018.12.001

Despite the advances and increase of observations of physical and chemical processes to better understand the functioning of coastal environments, a large gap still exists in quantifying exchanges and interactions between adjacent coastal systems. It is important to bear in mind that the dynamics and mass exchanges depend on the variability of the driving mechanisms and respond to several time scales (tidal, seasonal and inter-annual). The general objective of this work was to unravel the role of the driving forces on the nutrients and chlorophyll-a exchanges at the Ancão inlet of Ria Formosa lagoon during the most productive season - spring. This is the smallest inlet of the western system, the closest to continental interface and the one where migratory patterns are evident. So, the changes along time could be more evident there than at the other two inlets of the western sector. Ancão inlet will serve as a reference to compare the mass budgets exchanged with the ocean with the other two inlets. Specifically, this work intends to: i) better understand the behaviour of this inlet; ii) its role in the mass exchanges; and iii) its interplay with phytoplankton productivity during the peak season. In this context, the transport of water, nutrients and chlorophyll-a (proxy of phytoplankton density) were estimated across the Ancão inlet section during the spring season. Surveys were conducted under extreme fortnightly tidal conditions during 2007, 2009 and 2012, covering different hydrodynamic, meteorological and environmental conditions. To estimate the mass transport, field velocities, nutrients and chlorophyll-a concentrations were measured concurrently along its cross section. Results show that although the hydrodynamic and morphologic changes recorded at this inlet provoked a loss of hydraulic efficiency apparently these did not markedly affect the mass exchanges during the spring productive season. Globally, the contribution and intensity of the meteorological/physical, chemical and biological drivers superimposed those affected by tides, reflected in the differences between the five surveys conducted. Upwelling was frequent during the spring season and played a key role on the exchanges and mass transport through the Ancão inlet. Data also show that nutrients behaved dissimilarly; silicate was consistently exported, nitrate mostly imported, dependent on the intensity of upwelling and biological consumption, while phosphate generally followed the direction of residual circulation. Chlorophyll-a showed 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, the availability of nutrients on the coast will promote afterwards the growth of phytoplankton that enters and fertilizes the Ria Formosa, increasing its productivity. The estimated amounts are relative to the smallest inlet of the western sector of Ria Formosa. In consequence, it may be anticipated that through the other main inlets from this sector the exchanges are intensified and may enhance their contribution to the Ria Formosa fertilization. •Role of driving forces in mass transport in the Ancão inlet, Ria Formosa is presented.•Morphologic changes at Ancão inlet did not affect markedly the mass exchanges.•Physical/meteorological and biological drivers superimposed those of tidal conditions.•During spring, under upwelling events, the coast further fertilizes the Ria Formosa.•Changes at Ancão inlet might affect the interconnectivity with the other main inlets.