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On 24 June 2024, we detected foil that tightly adhered to an intertidal wall in Vigo harbor (Spain) during low tide. It covered multiple barnacles, potentially threatening their survival. We present photos of this novel debris-animal interaction and discuss possible effects that such cover could have on barnacles. [Display omitted] • First documented case of anthropogenic foil sealing filter-feeders. • Feeding, breathing and reproduction of the barnacles appear impaired. • Foil likely derived from wet wipe pollution. [ABSTRACT FROM AUTHOR]

Wildfire ash can have an impact on coastal prokaryotic plankton. To understand the extent to which community composition and abundance of coastal prokaryotes are affected by ash, two ash addition experiments were performed. Ash from a massive wildfire that took place in the Ría de Vigo watershed in October 2017 was added to natural surface water samples collected in the middle sector of the ría during the summer of 2019 and winter of 2020, and incubated for 72 h, under natural water temperature and irradiance conditions. Plankton responses were assessed through chlorophyll a and bacterial abundance measurements. Prokaryotic DNA was analyzed using 16S rRNA gene partial sequencing. In summer, when nutrient concentrations were low in the ría, the addition of ash led to an increase in phytoplankton and bacterial abundance, increasing the proportions of Alteromonadales, Flavobacteriales, and the potentially pathogenic Vibrio , among other taxa. After the winter runoff events, nutrient concentrations in the Ría de Vigo were high, and only minor changes in bacterial abundance were detected. Our findings suggest that the compounds associated with wildfire ash can alter the composition of bacterioplanktonic communities, which is relevant information for the management of coastal ecosystems in fire-prone areas. [Display omitted] • Wildfire ash had an impact on bacterioplankton abundance and phytoplankton biomass. • The greatest changes in chlorophyll a and bacterial abundance happened in summer, under low-nutrient conditions. • Exposure to wildfire ash aqueous extracts changed the composition of the bacterioplankton community. • Alteromonadales, Flavobacteriales, and Vibrio increased their relative abundances after exposure to ash. [ABSTRACT FROM AUTHOR]

The high sedimentation rates and high organic matter contents in the sediments of the Ría de Vigo (NW Spain) promote the development of anoxic conditions, determining the dynamics of elements like Fe and conditioning his speciation and reactivity. Four gravity cores were retrieved in anoxic sediments of the Ría de Vigo in November 2012. In order to understand the behavior of Fe in these complex environments different fractions of reactive iron were analyzed. The decrease in highly reactive iron and sulfide contents with depth showed the relationship between the iron and sulfur cycle in the middle and outer zones of the ría. In the inner zone, the apparition of shallow methane gas may cause the slower decrease of the highly reactive iron contents. In zones without methane, sediment layers enriched in iron −with a reactivity higher than in other sediment samples− were observed. An increase was observed in the dithionite and total reactive iron contents from the inner to the outer zone of the ría, according to the gas depth. Furthermore, a decrease in Fe (III)-bearing minerals contents with depth was observed in the outer and middle zones, but not in the innermost area where the gas is shallow. The high organic matter and sulfide contents, mainly in the inner zone of the ría, indicate that the most of the Fe (II) is FeS. Moreover, the high contents of total reactive iron and pH values (6.86–7.98) could contribute the formation of stable minerals like pyrite along the Ría de Vigo. [ABSTRACT FROM AUTHOR]

The potential power output expected from the installation of a tidal farm near the mesotidal Ria de Vigo (NW Spain) is assessed using two different tidal stream energy converters (TEC). For this, the results of a previous resource assessment based on a 28-day long hydrodynamic simulation are used. From this data we identify the areas susceptible of hosting the farms, select the optimal location for them, and assess the total available and extractable energy for each turbine type. Finally, using a simple farm design based on standard inter-turbine separation, we estimate the expected power supplied by the farm. Irrespective of the site, the total available tidal power in the areas susceptible of hosting the farms is around 150 MW; at the optimal location, the hourly extractable power is about 22.5 MW, of which only between 10% and 15% can be harnessed by the designed farms, powering between 4411 and 6638 homes. A local analysis of the most energetic subregions within these sites increases this ratio up to 30%. Nevertheless, the power output is sufficient to fulfil the needs of between 1660 and 2213 households, depending on the chosen site and the selected TEC. [ABSTRACT FROM AUTHOR]

Two short-range (46 MHz) Coastal Ocean Dynamics Application Radar (CODAR) SeaSonde HF were operating in the Ría de Vigo during one year between September 2012 and August 2013 to permit observations of the surface circulation in the outer region of the Ría de Vigo (NW Spain). An analysis of low-pass current and vorticity conducted over one year revealed two opposite vorticity structures in the HF radar coverage area. Simultaneously, wind stress and its curl, calculated at two meteorological stations (Cíes and Borneira) in the HF radar coverage area, were assessed to establish the main mechanisms promoting the formation of these two opposite vorticity structures. Researchers selected three periods of 58, 41.5, and 77 days within the study year in which radar and wind data were simultaneously recorded at two stations. Examining HF radar vorticity at specific grid points representing both vorticity structures reveals a greater correlation between HF radar vorticity and the y-component of wind stress at the outermost meteorological station (Cíes) for all periods (R=0.52–0.80).Only one period (1 Sep–28 Oct 2012) displayed a correlation between the vorticity and the curl wind stress calculated at these two meteorological stations (R=0.50–0.62). Once wind forcing has been reported as the main factor responsible for generating these dipolar vorticity structures at subtidal frequencies, these structures can be shown to develop in two patterns: (1) counter-clockwise and clockwise relative vorticity in the northern and southern outer ría respectively, mainly developing during the transition from upwelling to downwelling, and with a lifetime normally dependent to the duration of the subsequent downwelling/relaxation conditions; and (2) clockwise and counter-clockwise vorticity in the northern and southern outer ría respectively, mainly generated during moderate or intense upwelling events. The life span of these vorticity structures ranges from 2 to 8 days. The largest range between positive and negative vorticity, or the most extreme vorticity, is observed/recorded during downwelling events. This is the first time these double vorticity structures have been observed at low frequencies in the outer Ría de Vigo. Their existence is key to understanding the mechanisms of transport between the Ría de Vigo and the shelf, and they could help explain the retention of plankton or pollutants inside some regions of the ría. [ABSTRACT FROM AUTHOR]

The Ría de Vigo is a semi-enclosed bay with high primary productivity due to the influence of coastal upwelling-downwelling dynamics. The area is heavily populated and affected by numerous human activities, which lead to sediment modification. Epibenthic megafauna from the non-estuarine zones of this bay has been studied in order to describe its spatial distribution, testing possible differences between inner and outer areas. With that purpose, 75 sites have been sampled by means of a towing dredge. Megafauna was identified to the lowest taxonomic level possible, and each taxon counted and weighted. 113 different taxa were identified and a high spatial heterogeneity was observed in terms of abundance, biomass, taxa richness, diversity and evenness. Suspension-feeding molluscs dominated the innermost part of the studied area, and were substituted by echinoderms towards the external zones; this spatial pattern was also reflected in the results of multivariate analyses. These shifts in taxonomic and trophic guild composition of the assemblages have been tentatively related to differences in pollution levels and primary productivity along the main axis of the bay. [ABSTRACT FROM AUTHOR]

Abstract: San Simón Bay, the inner part of the Ría de Vigo (NW Spain), an area previously identified as highly polluted by Pb, was selected for the application of Pb stable isotope ratios as a fingerprinting tool in subtidal and intertidal sediment cores. Lead isotopic ratios were determined by inductively coupled plasma mass spectrometry on extracts from bulk samples after total acid digestion. Depth-wise profiles of 206Pb/207Pb, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and 208Pb/207Pb ratios showed, in general, an upward decrease for both intertidal and subtidal sediments as a consequence of the anthropogenic activities over the last century, or centuries. Waste channel samples from a nearby ceramic factory showed characteristic Pb stable isotope ratios different from those typical of coal and petrol. Natural isotope ratios from non-polluted samples were established for the study area, differentiating sediments from granitic or schist–gneiss sources. A binary mixing model employed on the polluted samples allowed estimating the anthropogenic inputs to the bay. These inputs represented between 25 and 98% of Pb inputs in intertidal samples, and 9–84% in subtidal samples, their contributions varying with time. Anthropogenic sources were apportioned according to a three-source model. Coal combustion-related emissions were the main anthropogenic source Pb to the bay (60–70%) before the establishment of the ceramic factory in the area (in the 1970s) which has since constituted the main source (95–100%), followed by petrol-related emissions. The Pb inputs history for the intertidal area was determined for the 20th century, and, for the subtidal area, the 19th and 20th centuries. [Copyright &y& Elsevier]

Abstract: Horizontal Lagrangian surface transport is studied in the Ria de Vigo, an estuary in NW Spain with tidal and wind-driven dynamics. Surface drifters and the surface flow from a high-resolution 3-D hydrodynamic model are compared to each other. In particular, our analysis is based on a classical comparison of real and artificial trajectories and on Lagrangian Coherent Structures (LCS) defined as ridges in spatial fields of the Finite-Time Lyapunov Exponent (FTLE). The trajectories of the drifters are in good agreement with the prediction of the model in two out of four cases. Further, FTLE ridges computed from the model velocity fields are found to mark transport barriers for the drifters. The results indicate that the model is able to represent the general circulation in the estuary. Main patterns in the Lagrangian surface transport in the model are shown for two typical meteorological situations, north wind and south wind. They can be interpreted as an imprint of a 3-dimensional circulation pattern in the Ria de Vigo and reveal in detail the separation of the time-dependent in- and outflow at the surface of the estuary. [Copyright &y& Elsevier]

Abstract: The total concentration and chemical speciation of Cu, Pb and Zn were determined by square wave anodic stripping voltammetry (SWASV) in the Ría de Vigo, an estuarine area located in NW Spain. Surface and bottom waters from 6 locations were collected in two seasons during 3 years. The total Pb was below 1nM, and Cu and Zn concentrations, ranged from 3 to 44nM and from 9 to 300nM respectively. A gradient from sampling points located in the port of Vigo to external areas was observed. The speciation of the metals (ligand concentration and apparent complex formation constant K′) was calculated using several methods: The Langmuir and Scatchard linear fits for one and two ligands, the Lorenzo non-linear fit for one ligand and Langmuir non-linear fit for two ligands. The capability of the different methods to achieve reliable results have been discussed and Langmuir linear fit as well as Lorenzo non-linear fit are the most suitable. Cu presented the highest ligand concentrations, followed by Zn and Pb, while mean log K′ values fell in the range 5–9 (±0.6) for all metals and samples. The adjustment of the data treatment methods used to calculate the speciation parameters was found to vary depending on the extent of complexation and on whether one or two ligands needed to be considered. [Copyright &y& Elsevier]

Abstract: Based on the stable isotope composition in 15N and 13C of different potential sources of organic matter and consumers of an intertidal Zostera marina meadow located in San Simón Bay (Ría de Vigo, NW of Spain), a simplified food web of this community was reconstructed. For this purpose, some alternatives in different steps of the most used methodology of stable isotope dietary analysis were developed that cope with some of the limitations associated to the interpretation of isotopic signals for food web analysis, those of uncertainty on the fractionation value, mathematical model to use for the diet resolution and shortage of the isotope number for discriminating many food sources. The application of this protocol to the studied community reported similar results to those from other studies based on similar trophic webs, emphasizing the importance of local primary producers, especially microphytobenthos, which could be available for several primary consumers through resuspension forced by tidal hydrodynamic. The good agreement with previous results suggests that the proposed protocol is a feasible alternative to elucidate the most plausible trophic relationships in complex trophic webs using stable isotopes analysis. [Copyright &y& Elsevier]

Abstract: To contribute to establishing a historical baseline for future evaluations of the environmental quality of the Ría de Vigo (NW Spain), we report metal contents determined in eight gravity cores obtained at representative locations in 1990 – before the installation of any wastewater treatment plants – and in fractions thereof that were obtained by the BCR sequential extraction method. The results suggest that early diagenesis had been influenced by both hydrodynamic conditions and organic matter input (the latter especially in areas devoted to mariculture), and that anthropogenic inputs had also affected the concentrations and between-fraction distribution of Cu, Pb, Zn and other metals in surficial sediments. [Copyright &y& Elsevier]

Abstract: The influence of suspended mussel culture on the benthic–pelagic coupling was evaluated in the Ría de Vigo, in the coastal upwelling system of the NW Iberian Peninsula, during the month of July 2004. Measurements of water column properties were carried out at three stations in the Ría de Vigo: under a mussel raft (1), and at two reference sites in the main channel (2) and in the inner part (3) of the Ría. Dissolved nutrients, dissolved oxygen and inorganic carbon benthic fluxes were measured by means of a benthic chamber at stations 1 and 3. Sediment traps were deployed at 6 locations to estimate vertical fluxes. The water column structure at the three study stations was very similar, characterized by upwelling conditions during the second week of July and a posterior stratification showing a strong thermocline, with a depth fluctuation mainly modulated by the shelf wind regime. Vertical POC fluxes underneath the mussel raft (3gCm− 2 d−1) were 3 times higher than those obtained between rafts and 10 times higher than in the main channel reference site. Dissolved oxygen, ammonium, silicate and phosphate benthic fluxes were significantly higher under the raft than at the inner Ría reference site. A 1D carbon budget showed the importance of benthic metabolism under the raft (2.3±0.8gCm−2 d−1), being higher than the organic carbon produced at the photic layer (0.7±0.3gCm−2 d−1), as a result of higher organic loading compared to the inner Ría reference site. The results show for the first time the important role that suspended mussel cultures play in the benthic–pelagic coupling in this coastal upwelling ecosystem. [Copyright &y& Elsevier]

Abstract: The spatial and vertical distributions of live benthic foraminifera from the muddy central axis of the Ría de Vigo were examined under downwelling and upwelling conditions. The spatial distribution of the main benthic foraminiferal species is controlled by salinity variations (San Simón Assemblage), food availability (Outer Ría Assemblage) and oxygen concentrations and/or reducing microenvironmental conditions in the sediment (Inner Ría Assemblage). The microhabitat distribution of benthic foraminifera is mainly dependant on the oxygenation/redox conditions in the sediment and the vertical segregation of food. In the inner areas of the ría, low oxygen and/or reducing microenvironmental conditions prevent the vertical segregation of microhabitats. In outer areas oxygen penetration is deep but microhabitat partitioning only occurs in the presence of additional food resources (mainly fresh organic carbon from phytoplankton blooms) which triggers the colonisation of the surface layer by new species and the migration upwards and reproduction of opportunistic species. [Copyright &y& Elsevier]

Abstract: Methane (CH4) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH4 concentration and stable isotopic signatures (δ 13CH4) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH4 were determined in sediment incubations. Surface water column CH4 (2 m depth) was in the range 3–180 nmol l−1 (110–8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH4 inputs from underlying porewaters in which CH4 concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l−1). Surface water CH4 concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH4 flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH4 and δ 13CH4 in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH4 oxidation, with an apparent isotopic fractionation factor (r c) of ∼1.004. Using turbulent diffusion models of air–sea exchange we estimate an annual emission of atmospheric CH4 from the Ría de Vigo of 18–44×106 g (1.1–2.7×106 mol). This estimate is approximately 1–2 orders of magnitude lower than a previous estimate based on a bubble transport model. [Copyright &y& Elsevier]

Abstract: Dinoflagellate blooms in coastal upwelling systems are restricted to times and places with reduced exchange and mixing. The Rías Baixas of Galicia are four bays in the NW Iberian upwelling with these characteristics where harmful algal blooms (HABs) of dinoflagellates are common. These blooms are especially recurrent at the end of the upwelling season, when autumn downwelling amplifies accumulation and retention through the development of a convergence front in the interior of Rías. Because oceanic water enters the Rías during downwelling, it has been hypothesised that dinoflagellate blooms originate by the advection and subsequent accumulation of allochthonous populations. To examine this possibility, we studied the microplankton succession in relation to hydrographic variability in the Ría de Vigo (one of these four bays) along an annual cycle making use of a high sampling frequency. The results indicated that upwelling lasted from May to August, with downwelling prevailing in winter. Microplankton during upwelling, although dominated by diatoms, evidenced a progressive increase in the importance of dinoflagellates, which achieved maximum abundance at the end of the upwelling season. Thus, diatoms characterised the spring bloom, while diatoms and autochthonous dinoflagellates composed the autumn bloom. Diatoms dominated during the first moments of the autumn downwelling and dinoflagellates were more abundant later, after stronger downwelling removed diatoms from the water column. Since the dinoflagellates selected by downwelling belonged to the local community, it is concluded that advection of alien populations is not required to explain these autumn blooms. [Copyright &y& Elsevier]

Abstract: Live benthic foraminifera in the superficial sediments from the muddy central axis of the Ría de Vigo were examined under two contrasting hydrographic conditions: downwelling and upwelling. During downwelling conditions the abundance of benthic foraminifera does not show large differences between sites with different organic carbon contents. The arrival of labile organic carbon to the seafloor delivered during upwelling events causes an increase in the abundance of the most significant species and the appearance of new species in the life assemblage. This suggests that benthic foraminiferal faunas strongly depend on high quality organic carbon supply and the sedimentary organic carbon is not a good indicator of food availability to benthic foraminifera. The response of benthic foraminifera to phytoplankton blooms differs between outer and inner sites. In outer and middle areas benthic foraminiferal assemblages show quick population growth in reaction to phytoplankton blooms (r-strategists), whereas in inner sites the most abundant species displays both growth and reproduction (k-strategists). It is suggested that r-strategy results of adaptation to perturbations on short time-scales (downwelling/upwelling cycles) under favourable microenvironmental conditions, while the k-strategy represents the adaptation to long term perturbations, such as relatively low oxygen concentrations and/or reducing microenvironmental conditions in the sediment. [Copyright &y& Elsevier]

Abstract: The seismic analysis of the sedimentary infill of the Ría de Vigo reveals that the infill comprises of a fifth order sequence (18 ky) bounded by a major discontinuity surface. Within the Holocene sequence, several seismic units have been identified; the oldest one originated after the Würm glaciation and the origin of its top discontinuity was eroded during the regression (sea level at −120 m) of this last glacial episode (isotopic stages 2 to 4), 18 ky B.P. In some places below this ría infill, another sequence can be identified. This older sequence is associated with the pre-existing faults and troughs in the deepest parts of the ría, and it was deposited during the Würm glaciation (Miocene–Pleistocene). Eroded sediments were moved from the rías area to deeper zones, where they accumulated in the lowstand system tract. The next sea level rise occured in two steps, producing two transgressive units separated by an hiatus surface. This cycle was interrupted by the next sea level fall (to −55 m) marked on the seismic records by another recognizable boundary. The next sea level rise took place in several steps (back-stepping) with some stillstands, generating another transgressive system tract in the ría. From that time on, the relative sea level continued rising, depositing the most recent unit which represents the highstand system tract. Separating the highstand system tract and the transgresive unit below there is a consensed section. The analysis of 29 cores provides groundtruthing for our hypothesis. The identified main lithologic units show a transgressive sequence: a granitic rock base, an overlying second unit-locally wedge shaped- and most recently, a marine muddy unit covering the present ría seafloor. [Copyright &y& Elsevier]

Abstract: We used wind data measured at six meteorological stations to study their spatial representativity on atmosphere–ocean interactions along the western shelf of Galicia and inside the Ría of Vigo. The correlation as a function of distance and complex empirical orthogonal functions of the wind field were computed, allowing us to divide the region into three sub-domains: the open ocean, the shelf and the Ría of Vigo. Afterwards, wind gradients among stations were computed to determine specific spatial wind features: results showed an expected wind channelling effect inside the Ría of Vigo, but also a zonal onshore negative frictional gradient on the shelf that generates Ekman pumping during upwelling favourable winds. Finally, the Ekman transport estimated from meteorological stations was compared with measured transport from two moorings located inside the Ría of Vigo and on the shelf, and we determined that the meteorological station most representative of the wind field in the shelf is the one installed in a moored buoy on the shelf. [Copyright &y& Elsevier]

Abstract: The Ensenada de San Simón is the inner part of the Ría de Vigo, one of the major mesotidal rías of the Galician coast, NW Spain. The geochemistry of its bottom sediments can be accounted for in terms of both natural and anthropogenic sources. Mixture-modelling enables much of the Cr, Ni, V, Cu, Pb and Zn concentrations of the bottom and subaqueous sediments to be explained by sediment input from the river systems and faecal matter from manmade mussel rafts. The compositions and relative contributions of additional, unknown, sources of anomalous heavy-metal concentrations are quantified using constrained nonlinear optimization. The pattern of metal enrichment is attributed to: material carried in solution and suspension in marine water entering the Ensenada from the polluted industrial areas of the adjacent Ría de Vigo; wind-borne urban dusts and/or vehicular emissions from the surrounding network of roads and a motorway road-bridge over the Estrecho de Rande; industrial and agricultural pollution from the R. Redondela; and waste from a former ceramics factory near the mouth of the combined R. Oitabén and R. Verdugo. Using 137Cs dating, it is suggested that heavy metal build-up in the sediments since the late 1970s followed development of inshore fisheries and introduction of the mussel rafts (ca. 1960) and increasing industrialisation. [Copyright &y& Elsevier]

Abstract: A combined study of coccolith assemblages and biomarkers in a gravity core collected from the Ría de Vigo (NW Spain) allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years. The quantitative distribution of coccolithophore species points to three different intervals within the core, dated by AMS radiocarbon measurements. The first interval (ca. 975 BC–252 AD), characterized by high abundances of Calcidiscus leptoporus and Gephyrocapsa muellerae, is thought to represent moderate water temperatures, suggesting a transition from a warmer to a cooler period. The second interval (ca. 252–1368 AD), characterized by the dominance of Coccolithus pelagicus, Helicosphaera carteri and Syracosphaera spp., and a high concentration of hexacosanol linked to terrestrial input, is interpreted as having been a humid period with fluvial input. The third interval (ca. 1368 AD–1950) is characterized by a high abundance of Gephyrocapsa oceanica, high alkenone values and low values of hexacosanol, and is thought to represent a period dominated by oceanic conditions within the Ría. Taking into account the ocean–atmospheric system affecting the region studied, here we propose an alternation in the mean state of North Atlantic Oscillation (NAO) at millennial time scales. A well-developed upwelling system and an active Ría–ocean connection during the warmer interval I suggest a NAO+ phase influenced by a Hypsithermal period. The occurrence of the humid and relatively warm interval II is consistent with a negative phase in the NAO, as well as a relative restriction in ocean–Ría exchange. Interval III, which was drier and more productive, again suggests the dominance of a positive phase in the NAO, with a more intense oceanic connection and more energized upwelling. [Copyright &y& Elsevier]

The accumulation of plastic waste in estuaries is growing due to the increase in their use in daily life and their inadequate treatment on wastewater plants (WWTPs). Hydrodynamic and particle-tracking models were validated and used to improve the knowledge about the distribution and concentration of microplastics released by WWTPs in the Ria de Vigo. Results showed that the Vigo WWTP is the main driver of microplastics to the Ria de Vigo. Besides, 21% of the released microplastics reach the adjacent ocean, 24% remain anchored around the Cies Islands, and a negligible percentage reaches the upper estuary when the emission occurs under ebb on spring tide conditions. A negligible number of released microplastics is exported to the nearby ocean when the emission occurs under neap tide conditions. This research can provide a useful tool to support the identification of monitoring processes and debris removal. • Delft3D model successfully detected critical zones for microplastics pollution. • Wastewater treatment plants are the main source of microplastics in the Ria de Vigo. • The microplastics distribution is strongly depend on the tidal stage in Ria de Vigo. • Ria de Vigo exports a large quantity of microplastics to the adjacent ocean. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) pollution in marine environments has received considerable attention over the past two decades due to the increased awareness of its potential risks to ecosystems. Numerical simulations can be used to provide estimates of MPs fate and distribution, but so far this approach has been largely applied to the open ocean. In this work, the distribution patterns of MPs in a prototype coastal upwelling environment (Ría de Vigo estuary, Spain) is investigated using a combined approach of field data and modelling. Water and sediment samples were collected at different locations along the Ría during both upwelling and downwelling conditions. Experiments using an idealized 2D-vertical model were conducted to explain the observed MP distribution and elucidate the relative importance of river discharge, wind-driven and density-driven circulation. Microplastics were found at all stations in all samples. The largest observed fraction of MPs corresponded to fibres followed by plastic paint sheets and fragments. The trapping or flushing of MPs was mainly controlled by the wind forcing, whose effects on the circulation normally exceeds those of the density-driven and river flows. During upwelling conditions, more MP items were collected near the surface at the outer half of the estuary than during downwelling. The seaward near-surface circulation induced by the wind and density gradient jointly contributed to flushing out floating MPs. Near the bottom, the landward wind-induced and gravitational circulation formed estuarine MP maxima (EMPM) inside the estuary. Pellets, fragments, and films were more efficiently trapped than fibres, as their EMPM were located more upstream. The results suggested that downwelling-favourable winds caused an overall landward (seaward) displacement of the distribution of floating (sinking) MPs. Modelling results indicate that winds dominate the circulation in the outer part of the estuary, whereas near the head the gravitational circulation takes over the control of the net flow. The particular location of the EMPM appears to be controlled by the competition of density-driven and wind-driven flows. • The distribution of microplastics (MPs) in the Ría de Vigo is quantified • A combined approach of sampling, laboratory analyses and modelling is adopted • Hotspots of floating and sinking MPs are identified for upwelling and downwelling • Estuarine MP Maxima (EMPM) is controlled by competing density- and wind-driven flow [ABSTRACT FROM AUTHOR]