Ricardo Prego

Heavy metal sedimentary record in a Galician Ria (NW Spain): background values and recent contamination

Two long sediment cores were sampled at the Ferrol Ria (Galicia, NW Spain) and the heavy metal (Co, Cr, Cu, Fe, Ni, Pb and Zn) concentrations measured in order to (i) state accurate background values providing baseline relationships with respect to a reference element and (ii) to investigate the recent metal contamination trends. Background values were found to agree well with the world average values for granite/schists-genisses rocks. However, Cu, Co, Pb and Zn were found to be lower than those previously reported as background values for the Galician Rias. Results emphasize the importance of using baseline relationships with respect to a normalizing element in order to reduce the scattering of data and to allow an accurate statement of background values. The distribution of metals in the cores showed an evident enrichment in the surface layers belonging to the industrial era. Normalized enrichment factors (NEF) for copper and zinc are in the order of 3-5 (certain/severe contamination) in the surface sediments, decreasing with depth. Lead contamination has decreased in the recent years from NEF of 3-7 down to a NEF of 2 (i.e. moderate contamination), probably due to the introduction of unleaded gasolines. Chromium, cobalt and nickel NEFs were always in the <1-2 range indicating null/low contamination by these metals.

A simple model to calculate the residual flows in a spanish ria hydrographic consequences in the ria of vigo

In this article a stationary model for the calculation of residual flow and mixing of water in a ria, on the basis of contribution of fresh water and salinity as a tracer, is presented. The model is applied to the ria of Vigo, whose circulation is similar to that of a partially stratified estuary. This ria is divided into five boxes and a system of 20 equations is proposed whose solutions are the residual outflows and inflows, and the rise and mixing fluxes, which occur in the ria. In the winter the velocities of the residual currents are from 4 to 8 cm s −1 , and the exit of fresh water is high for the northern mouth of the ria. The flows diminish and the mixing of water increases in the ria (2–3 m day −1 in box 2) as the contribution of fresh water decreases in the spring and summer. The presence of northerly winds increases the residual circulation threefold in the summer, there being an out-flow of 10 6 kg s −1 to the ocean. However, southerly winds retain the water in the ria and the proposed model can only be applied to the rias inner and middle sections.

Upwelling influence on the Galician coast: silicate in shelf water and underlying surface sediments

Abstract Local characteristics in the upwelling of Galicia (NW Iberian Peninsula) are studied in terms of dissolved silicate patterns in the seawater column and opal distribution in the sediments. Freshwater input, upwelling, remineralization and sedimentation are considered. The freshwater silicate input is not important during the upwelling season. Upwelling is the main process controlling silicate biogeochemistry activity in the coastal zone. Areas of silicate remineralization in the seawater column and opal abundance in surface sediment practically coincide. These together define the coastal limit of upwelling influence and its diverse local effects. Galician upwelling is important in the area surrounding three well-defined zones; Cape Finisterre, Cape Prior and La Corun˜a Canyon. South of Finisterre upwelling is more intense and closer to the coast. To the north, it is discontinuous and keeps distant from the coast, being near to the edge of the continental shelf.

Rias, estuaries and incised valleys: Is a ria an estuary?

Abstract Today, the term ria is rarely used by sedimentologists or stratigraphers, although it embodies all the characteristics of the so-called incised valleys – a topic of considerable interest since the increased understanding of the three dimensions of transgressive sequences using seismic stratigraphy. When it is used, it is usually referred to as a type of estuary; however, in many cases, only a minor part is influenced by estuarine processes. It is a useful term which should be revived as it encompasses in its entirety all the features and resulting deposits of an incised valley whether it is estuarine or marine.

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

Abstract 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.

A two-dimensional particle tracking model for pollution dispersion in A Coruna and Vigo Rias (NW Spain)

A two-dimensional hydrodynamic model coupled to a particle tracking model is applied to study the dispersion processes and residence time in two Galician rias (A Coruna and Vigo, NW Spain) under summer conditions. In A Coruna a long residence time was found in the harbour area due to the existence of a dock, and a short one in the river area. On the contrary, in Vigo, the residence time is smaller in the harbour area, due to the Rande Strait, beyond which the river effect is negligible.

Hydrographic characterization of a winter-upwelling event in the Ria of Pontevedra (NW Spain)

An unusual winter-upwelling event was observed in the Ria of Pontevedra during a cruise carried out on 27 January 1998. Upwelled water masses inside the estuary are observed to depend on the season due to the annual variation of water circulation at the adjacent shelf. The winter upwelled water corresponds to the water mass transported by the poleward current, which is saltier and warmer, but less dense than the Eastern North Atlantic Central Water observed in spring and summer.

General aspects of carbon biogeochemistry in the ria of Vigo, northwestern Spain

The rias of Galicia in northwestern Spain are local areas of high primary production. In this article, the fluxes of organic and inorganic carbon and the processes of photosynthesis, remineralization, and sedimentation of particulate organic carbon in one of these, the ria of Vigo, are quantified using the box model method. In 1986 the mean photosynthesis rate in the ria of Vigo was 350 mgC m−2 d−1; on average, 40% of this quantity was remineralized; 140 mgC m−2 d−1 passed into the sediment; and the remaining 65 mgC m−2 d−1 (18%) was exported to the coastal waters. Such budgets are very sensitive to meteorologic conditions; for during the April to October period when wind-induced upwelling is frequent, the processes mentioned increase greatly in the interior part of the ria. In winter a large quantity of carbon gets exported to the ocean, 78 molC s−1. During the rest of the year the ria behaves like a carbon trap, with most of the 27 molC s−1 that is trapped being lost to sedimentation.

Hydrography of the Pontevedra Ria: Intra-annual spatial and temporal variability in a Galician coastal system (NW Spain)

In order to ameliorate the dearth of existing scientific knowledge concerning the hydrography of the Pontevedra Ria, a systematic investigation was carried out between Octo- ber 1997-98. Salinity variations were closely related to river discharge whereas bottom wa- ters presented oceanic characteristics over the whole year. Current was controlled by tide, river discharge, and wind in the internal ria where the highest velocities were directed along the ria channel with a low transverse component. Favorable atmospheric conditions in spring induced coastal upwelling up the continental shelf. In May the upwelling was sufficiently strong to be detected in the inner ria and intensified in July and August, cooling the ria water to 12 o- 14oC. Upwelling ceased in September, and from November to March seawater trans- ported by the poleward current (35.9; 15oC) was detected on the shelf. From January until March, unanticipated favorable upwelling conditions provoked an influx of poleward inside the ria. Ria intrusion of poleward water and association with occasional winter upwelling conditions has not been observed previously. Isopycnic three-dimensional (3-D) surface and 2-D isopycnal maps show that with high fiver runoff or intense upwelling, lower-salinity water leaves the ria near the northern margin in the surface layer. Under negative upwelling conditions, the water is partially dammed inside the ria and exits the ria when the wind speed falls. During upwelling events, ENACW penetrated the ria, especially near the southern shore. Arrival of ENACW at the northern entrance impedes the outward water flow through this mouth.

Nutrient fluxes to the Bay of Biscay from Cantabrian rivers (Spain)

Abstract Nutrient fluxes to the Bay of Biscay from the Cantabrian basin have been quantified for the first time. Data between 1981 and 1995 of the main 16 Cantabrian rivers from the COCA monitoring programme have been used. Values of water flow and dissolved inorganic nitrogen (DIN), phosphate and silicate concentrations have been taken. Equations are proposed to quantify the fluvial nutrient contributions to the Cantabrian Sea. The annual average of continental outputs to the Bay of Biscay from the Cantabrian basin is 16.1 × 10 9 m 3 of freshwater, 1.0 × 10 9 mol of N in DIN, 0.062 × 10 9 mol of phosphate and 1.2 × 10 9 mol of silicate. In comparison with the French rivers, those of the Cantabrian have small fluxes and their outflow is very disperse, not forming large coastal plumes. From April to September, when the primary production is relatively important, the DIN contribution to the Cantabrian coastal reservoir is 10%. Coastal fertilisation due to continental waters could be considered as negligible and only influences areas very close to river mouths, except for the Nalon River. Its flux represents 33 % of nitrate, 39 % of phosphate and 15 % of silicate of the total continental inputs of nutrients to the Cantabrian Sea.