Rias Altas Research Articles

Effects of Tidal Stream Energy Exploitation on Estuarine Circulation and Its Seasonal Variability

Residual flows are of major importance in coastal areas, driving environmental processes such as sediment transport or nutrient dispersion. Consequently, in those areas where a large tidal stream energy resource is available, prior to the installation of a tidal farm, it is imperative to assess how energy extraction affects the residual flows and, in particular, upwelling events. In this paper, the potential effects of different configurations of tidal stream farms on the residual circulation and its seasonality are analysed by means of a case study: Ria de Ortigueira, the westernmost of the Galician Rias Altas (NW Spain). For this purpose, a 3D numerical model was implemented and validated against field measurements. Next, a total of eight case studies, including the operation of bottom-fixed and floating converters under typical summer and winter scenarios, considering upwelling favourable winds, were studied. Overall, when a tidal farm operates, regardless of its configuration and the forcings considered, the resulting general residual flow pattern does not experience significant modifications. This pattern is characterized by a 2D circulation in the inner ria and a positive estuarine circulation in the middle and outer ria. The largest modifications of the residual flow are apparent in the vicinities of the plant, with maximum values of about 0.05 ms−1. Outside this area, the alteration is lower than 0.01 ms−1 and virtually negligible at some distance from the farm where upwelling events develop.

Maruxaina and port mythology. Approach to a case in San Ciprian (Galician Rias Altas)

This article asks about the reasons for the reappearance of an apparently anachronistic mythical figure, Maruxaina, in the town of San Ciprian, in the Galician Rias Altas, in the late twentieth century. This mythical recovery occurs with the invention of a party that has not stopped growing since its birth. This growth has generated a discussion among the people of San Ciprian. The research revolves around the symbolic nature of this spirit, associated with the sea, which had been created in the past by San Ciprian sailors in order to justify unusual marine phenomena. This approach involves recreating the Maruxaina links with its immediate symbolic influences. All this with the intention of approaching the social fabric that makes up the Galician culture and its possibilities of cultural reaffirmation. The resurgence of Maruxaina raises a whole consideration on the mechanisms of anchoring to the past and the territory of the inhabitants of a town that continues to look towards the ocean.

Textural Characteristics might Influence Donax trunculus Shellfishing Banks Exploitability

In this study we combine textural and compositional information to characterize the intertidal sediments from three relevant shellfishing banks located in the Rias Altas (Vilarrube, Lombo das Navallas) and Rias Baixas (Playa America) of Galicia (NW Spain). The purpose of this study is to explore the relevance of the sediment characteristics as a key parameter in the decline of commercially exploitable populations of the bivalve Donax trunculus in two of the banks (Lombo das Navallas and Playa America) but not in the other (Vilarrube). The sediments of the three areas show their own distinctive sedimentary characteristics that became defined by their grain size parameters, mineralogical and elemental composition. This is the result of regional land supplies from the erosion of drainage areas and sea cliffs together with the contribution of modern carbonate bioclasts. Notably, the sediments of Vilarrube are characterized by moderately sorted to well sorted fine sand showing little spatial variability. According to our results, sediment texture seems to be a relevant parameter for the settlement and growth of commercial populations of Donax trunculus.

Influence of Hydrodynamics and Sedimentary Characteristics of Barqueiro Ria on Arealonga Beach Dynamics

The Barqueiro Ria, located on the north coast of the Iberian Peninsula, is one of the Galician Rias Altas, which includes Arealonga Beach, the longest beach in the Ria, located in the inner portion. During the 1990s strong erosion has been registered on the beach and associated dunes, while a wide intertidal spit has grown westward. This behaviour is related to the hydrodynamic and sedimentary characteristics of the Ria and Sor Estuary .T ide and wave influence are evaluated using numerical simulations for storm events. Seasonal topographic monitoring of beach and dune profiles and surface sediment samples allow to describe the variations in sedimentary volume and map sediment units. Furthermore, grain size parameters trends are used to determine the sediment transport patterns. Three different zones have been defined along beach and foredune according to their sedimentary dynamics behaviour: i) Eastern zone, with a clear erosive tendency generating the backshore and foredune destruction ii) Middle zone, with dune erosion but sediment accumulation in the intertidal zone, and iii) Western zone, where the beach presents an accumulative profile, with a well developed supratidal area and active dunes.

Nutrient dynamics in the Galician coastal area (Northwestern Iberian Peninsula): Do the Rias Bajas receive more nutrient salts than the Rias Altas?

The Rias of Galicia are commonly divided into the Rias Altas and the Rias Bajas, the former being north, and the latter south of Cape Finisterre (NW Iberian Peninsula). The difference in their sediments and biological characteristics justifies a chemical study of the influence of nutrients in the Galician coastal zone. Data from 1977 to 1992, obtained from research cruises on the continental shelf and in the Rias are considered. The sources of nutrient salts, such as from land, remineralization, oceanic fluxes, and winter mixing have been taken into account. It is concluded that the Rias Bajas are richer in nutrient salts than the Rias Altas. This difference is not due to the river input since this is low and similar in both groups of Rias. Neither is it due to winter mixing, which is comparatively more beneficial to spring blooms in the Rias Altas than in the Rias Bajas. Instead, it is caused by summer processes, when nutrient salt remineralize and new nutrient salts become available in the euphotic zone, due to upwelling: these processes exert a far greater influence in the Rias Bajas than in the Rias Altas. Also the presence of depleted, nutrient-poor coastal waters in front of the Rias Altas impedes the penetration of upwelled seawater into these Rias, whereas south of Cape Finisterre, upwelled seawater can penetrate directly into the Rias Bajas. Hence the Rias Bajas receives more new nutrients in summer than the Rias Altas.

Primary production and phytoplankton in three Galician Rias Altas (NW Spain): seasonal and spatial variability

Phytoplankton species composition, chlorophyll-a concentrations and primary production were studied in the Rias of Ares, Ferrol and the Bay of La Coruna (Galicia, NW Spain) in three oceanographic situations during 1993. The observations were representative of maxima and minima phytoplankton biomass and production values in this area during the seasonal cycle. A phytoplankton bloom studied in March, was characterized by a patchy distribution of chlorophyll and high primary production rates, especially near La Coruna and in the Ria de Ferrol. High phytoplankton biomass and production was also recorded in August, when an upwelling pulse allowed for enhanced growth. Diatoms were very abundant during these blooms but while Chaetoceros socialis was the dominant species in spring other species dominated in summer, when dinoflagellates and flagellates increased. In contrast, the phytoplankton observed in December had low abundances, and correspondingly low chlorophyll concentrations and primary production rates through the study area. Photosynthetic measurements at selected stations using P-I curves indicated that phytoplankton populations were well adapted to the existing light regime. The main source of variation in photosynthetic parameters was seasonal, and no significant differences resulted between rias. Using these parameters and the measured vertical profiles of chlorophyll and irradiance, areal estimations of primary production rates were made for the entire area studied. The resulting values were scaled to the rates measured using parallel simulated in situ incubations of phytoplankton. Maximum primary production values during blooms exceeded 2400 mg C m-2 d-1, whereas values estimated for the winter cruise were lower than 20 mg C m-2 d-1. These values are equivalent to those available for the nearby Rias Baixas, but because of the larger size of the latter the annual values of the studied Rias Altas were less than 10% of the reported primary production in the most productive Galician ria (Ria de Arousa). This study provides the first estimates of up-to-date primary production values for the Rias Altas, and points out the differential role of upwelling in the nearby shelf compared to its effects on the Rias Baixas region. Upwelling events occur in localized areas outside the Rias Altas, and their associated water dynamics may cause a large export of the produced organic matter to outer shelf areas. In contast, upwelling has been detected well inside most Rias Baixas, inducing high accumulations of recently produced organic matter, that are exported to nearby coastal areas.

Phytoplankton biomass and production in shelf waters off NW Spain: spatial and seasonal variability in relation to upwelling

Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rias Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rias Baixas shelf, but also shelf-break stations in the Rias Altas area. The Rias Baixas area had lower chlorophyll than both the Rias Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rias Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rias Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rias Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rias, while the contribution of in situ production to these accumulations was relatively lower.

Toxin profiles of natural populations and cultures ofAlexandrium minutum Halim from Galician (Spain) coastal waters

The toxin profiles of three isolates and natural populations of the PSP agentAlexandrium minutum from several Galician rias (NW Spain) was obtained by HPLC. The toxin content of cultures ofA. minutum is dominated by GTX4 (80–90%) and GTX4 (10–15%) with small amounts of GTX3 and GTX2 (less than 3% of each); similar results were obtained for natural populations ofAlexandrium from three different Galician rias, where a mixture ofA. lusitanicum Balech andA. minutum can occur. Important quantitative differences were found between the three isolates, one being highly and two weakly toxic. The results obtained from these isolates and natural populations ofAlexandrium were very similar to those obtained from HPLC analyses of mussels intoxicated during a PSP outbreak in Ria de Ares (Rias Altas) in 1984, confirming thatA. minutum (previously identified asGonyaulax tamarensis Lebour andAlexandrium lusitanicum) was the PSP agent during the toxic outbreak in May 1984. Toxin profiles obtained from natural populations during different PSP outbreaks in different rias and from cultures are fairly consistent and suggest that at least from the toxin point of view,A. lusitanicum andA. minutum are identical, and that the toxin profile ofA. minutum from Galicia can be used as a biochemical marker.

RIA DE FOZ: SOLUTION FOR A HARBOUR AND COASTAL PROBLEM

The ria of Foz is located in the Northwestern part of the Iberica - Peninsula, inside the Rias Altas group, in the Eastern extrem of Lugo/ province. It is placed on the natural form known as Golfo of Masma, topographical accident that takes its name from the river that flows - into the ria. From the point of view of the materials that constitute the environ ment, they are mainly composed by slaters and quarzites, with some levels of carbonates from the Low Paleozoical period. To the West, the - granitic materials are predominant. The ria is limited in its margens by some little slope and relative ly low cliffs. Its bounds have a little depth, due to the filling process, natural in the Rias Altas. The materials that refill the ria, come from the sea erosion of the cliffs (1), and the refilling is due/ to the sea waves action that produces in the tidal flow and ebb an - - asymetrical capacity of erosion and transport (2). That is a natural - situation, but the human action, building some channeling constructions has accelerated this refilling process. The traditional economic development on this zone, has been based - on some principal activities: fishing and agriculture, but nowadays turistic use rounds off the others. This situation and the evolution - of sailing neccesities on the ria, has been a conflict reason, which - is a consequence of the competition between these uses.