A numerical simulation study of the hydrodynamic effects caused by morphological changes in the Guadalquivir River Estuary.

This study presents an analysis of the impacts of the changes in bottom depth along the Guadalquivir Estuary on tidal dynamics. A realistic non-linear 1D numerical model, incorporating changes in both breadth and bottom depth, was employed to investigate the involved effects. The findings reveal a significant amplification of the M2 tidal wave towards the upper region of the Estuary, resulting from the gradual deepening caused by multiple dredging operations. The Estuary exhibits a pronounced tendency towards resonance, which is further enhanced by its deepening, resulting in reduced bottom friction and a smaller decrease in tidal wave amplitude as it propagates through the Estuary. The alterations in depth, particularly in breadth, along the Estuary play a crucial role in determining the magnitude of the resonant response of the M2 tidal wave.

Trace metals distribution between the surface waters of the Gulf of Cadiz and the Alboran Sea.

This study was conducted to address the changes in the surface distribution of trace metals (cobalt, copper, iron, cadmium, nickel, zinc, lead and molybdenum) as they are advected from the Gulf of Cadiz to the Alboran Sea, through the Strait of Gibraltar (south Iberian Peninsula), regions of great ecosystemic importance. Trace metals concentrations were measured in samples collected during two oceanographic cruises, together with the main factors affecting their spatial distribution and temporal variability (i.e., wind and surface currents). Several rivers, the main source of trace metals in this region, flow into the Gulf of Cadiz which is connected with the Alboran Sea through the Strait of Gibraltar by the general circulation pattern. The surface circulation pattern leads to an offshore-eastward gradient that is highly influenced by wind variability. An increase in vertical turbulence induced by the winds or the tidal cycle causes the dilution of trace metals' concentration by mixing rich-metal superficial waters with poor-metal subsurface waters. Additionally, along the eastward displacement of surface waters, several water retention zones have been described (Trafalgar, Camarinal, the Coastal Cyclonic Gyre) that imply an increase in trace metals concentration close to the coast. In addition, our results suggest that the coastal edges of the Strait of Gibraltar also act as a source of certain metals to the Alboran Sea, probably due to the industries in the proximity areas.

The fate of Guadalquivir River discharges in the coastal strip of the Gulf of Cádiz. A study based on the linking of watershed catchment and hydrodynamic models.

A catchment model for river basins and a hydrodynamic model were combined in order to simulate the spreading of the turbidity plume produced by sediment discharges from the Guadalquivir River basin within the Gulf of Cádiz under different meteorological conditions. The current fields provided by the hydrodynamic model and a transport-diffusion scheme based on tracking virtual particles tracking released at the river mouth have enabled us to simulate turbidity plumes that show great similarity with the plumes observed in satellite images. The most relevant results of the study show that in the absence of winds, the plume tends to spread very slowly, gradually progressing northwards; this is because of the symmetry between the filling and draining flows at the mouth of the Guadalquivir and low intensity of the tidal currents beyond the mouth. In addition, the transport of the plume towards the Strait of Gibraltar requires wind conditions with a northerly, north-westerly or westerly component. Westwards transport, however, requires winds with an easterly, southerly, or south-easterly component. The periods of heaviest rainfall in the Guadalquivir River basin coincide with winds mainly from the west; therefore, the times of maximum discharge at the mouth of the river occur when there are wind conditions that favour the transport of the matter suspended in the plume, southwards along the coast, towards the Strait of Gibraltar and the Alboran Sea. Linking the watershed catchment and hydrodynamic models has proved its suitability to predict the evolution and reaching of the sediment plumes from the Guadalquivir River discharges and the experience encourages the use of that methodology to be applied in a future prediction system for the creation and evolution of those sediment plumes.

Types and Distribution of Bioactive Polyunsaturated Aldehydes in a Gradient from Mesotrophic to Oligotrophic Waters in the Alborán Sea (Western Mediterranean).

Polyunsaturated aldehydes (PUAs) are bioactive molecules suggested as chemical defenses and infochemicals. In marine coastal habitats, diatoms reach high PUA production levels during bloom episodes. Two fractions of PUA can usually be analyzed: pPUA obtained via artificial breakage of collected phytoplankton cells and dissolved PUA already released to the environment (dPUA). In nature, resource supply arises as a main environmental controlling factor of PUA production. In this work, we monitored the vertical distribution and daily variation of pPUA associated with large-size phytoplankton and dPUA, at three sites located in the Alborán Sea from mesotrophic to oligotrophic waters. The results corroborate the presence of large-size PUA producers in oligotrophic and mesotrophic waters with a significant (58%-85%) diatom biomass. In addition to diatoms, significant correlations between pPUA production and dinoflagellate and silicoflagellate abundance were observed. 2E,4E/Z-Heptadienal was the most abundant aldehyde at the three sites with higher values (17.1 fg·cell-1) at the most oligotrophic site. 2E,4E/Z-Decadienal was the least abundant aldehyde, decreasing toward the oligotrophic site. For the first time, we describe the daily fluctuation of pPUA attributable to cellular physiological state and not exclusively to taxonomical composition. Our results demonstrate the persistence of threshold levels of dPUA deep in the water column, as well as the different chromatographic profiles of dPUA compared with pPUA. We propose different isomerization processes that alter the chemical structure of the released PUAs with unknown effects on their stability, biological function, and potential bioactivity.