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Abstract: Dissolved cadmium and copper species were measured in the Loire estuary and the North Biscay Bay continental shelf (France) in spring 2002. Metal behaviours along the salinity gradient, metal fluxes from the Loire system and surface distributions on the continental shelf were described and compared with the ones obtained at a period of higher discharge (i.e., winter 2001). Vertical distributions at different stations were also examined with the aim to assess whether the Loire inputs affect the Cu and Cd speciation over the continental shelf. In the Loire estuary, different metal behaviours were observed from winter. Cu and its various species mostly followed a theoretical dilution line whereas a Cd addition composed of chloro- and organic complexes was observed. According to our estimations, the Cu flux was composed, as in winter, of 40% hydrophobic organic complexes. On the other hand, Cd organic complexes accounted for less in the total dissolved metal flux than they did in winter (55 and 78% for spring and winter, respectively). On the continental shelf, a C18Cu-to-TDCu ratio of 40% was observed in the stratified area under Loire influence. For Cd, the organic fraction was relatively important in the surface waters near the mouth of the estuary and decreased deeper and seaward. Thus, the Cu and Cd speciation on the North Biscay Bay continental shelf are firstly determined by the extent of the estuarine plume. Beyond the estuarine influence, biological processes appeared to be the origin of the observed variations. [Copyright &y& Elsevier]

Abstract: Over this one-year study, we examined the variations of lead along the salinity gradient of the Penzé estuary (Brittany, Western Channel, France). Concentrations of total dissolved and total particulate lead ranged from 0.04 to 0.62nM and from 29 to 61μgg−1, respectively. These values, though being higher than contamination-free systems, remain lower than those found in heavily industrialised systems indicating a limited effect of agricultural practices. Our field data showed, for most seasons (i.e. spring, summer and autumn), a metal removal in the salinity range 0–10, effected mainly by co-precipitation with iron and manganese oxides. On the other hand, after a strong winter ascending flood, an addition of dissolved lead occurred in the estuary following resuspension of particles and desorption mechanisms. This metal addition along with the high water discharge were responsible for the particularly high Pb output flux reported for winter (67gday−1) compared to the ones estimated for other seasons (1–18gday−1). [Copyright &y& Elsevier]

Abstract: The study reported here was carried out in the macrotidal estuary of Penzé (Brittany, Western Channel, France). Ten field stations along the freshwater–seawater mixing zone were sampled each month in order to examine the speciation of dissolved and particulate cadmium. Different biogeochemical parameters (suspended particulate matter, Chlorophyll-a, pH and dissolved organic carbon) were also measured. Levels of total dissolved and total particulate metal ranged from 0.06 to 0.46nM and from 0.4 to 2.4μgg−1, respectively. Our data showed a non-conservative behaviour for cadmium as a result of desorption from particles. The rise in total dissolved cadmium in the salinity range 0–20 was about 0.2nM. Incidentally, a decrease of total particulate concentrations of about 0.5μgg−1, which corresponds approximately to 0.2nM, was observed. The study of the various cadmium species led us to identify desorption of cadmium occurred from the iron/manganese oxide-associated fraction. This desorption process leads to the formation of labile complexes, i.e. chlorocomplexes in spring and summer. However, in winter and autumn, a large part of the dissolved fraction was constituted by organic complexes. These complexes can be formed from suspended particles desorption or could be a released from sediment. Analysis of flux indicated that most of the metal inputs to the estuary (usually more than 80%) corresponded to organic cadmium. Spring and summer outputs were mainly constituted of chlorocomplexes whereas cadmium organic complexes were predominant in winter and autumn output fluxes. [Copyright &y& Elsevier]

Abstract: This one-year survey conducted in the macrotidal estuary of Penzé (Brittany, Western part of the Channel, France) was aimed at examining the variations of the various dissolved and particulate copper species. Ten field stations along the whole freshwater–seawater mixing zone were sampled each month. Different biogeochemical parameters (SPM, chl-a, pH and DOC) were also measured. The levels in total dissolved and total particulate copper ranged from 1.8 to 9.5nM and from 5 to 98μgg-1, respectively; such amounts are indicative of a pollution-free system. Extractable C18 copper (non-polar hydrophobic organic copper species), in winter and spring, accounted for 30–40% of the total dissolved copper. In summer, this contribution rapidly rose to 60% in the salinity range 20–30; over the same period of time, total particulate copper decreased. The change in dissolved copper speciation and the lowering of particulate copper concentrations were attributed to the release of strong organic ligands by phytoplankton. Our field data evidenced a highly variable behaviour for the various copper species over the seasonal cycle, and then led us to identify the following mechanisms: (i) metal desorption from organic river-flown particles (winter and spring), (ii) metal desorption from resuspended sediment in the upstream section (summer), (iii) competition between particles, non-extractable C18 organic ligands and phytoplankton-released extractable C18 organic ligands to complex copper in the downstream section (summer), and (iv) removal of non-extractable C18 organic copper by adsorption (autumn). Dissolved copper species fluxes were assessed: most of metal inputs to the estuary (60–74%) corresponded to non-extractable C18 organic copper. Winter and spring metal output fluxes were mainly constituted of non-extractable C18 organic complexes; on the other hand, extractable C18 organic complexes were predominant in summer and autumn output fluxes. [Copyright &y& Elsevier]

Abstract: Over this one-year study, the variations of inorganic As species were examined monthly along the salinity gradient of the Penzé estuary (NW France) in relation with different biogeochemical parameters. In most cases, dissolved As exhibited a non-conservative behaviour which resulted from the competition between two major processes. In the upstream section of the estuary, a strong input of both total inorganic As and As(III) occurred. Then, the removal of the same species, under precipitation of iron oxides/oxyhydroxides, was observed in the low-salinity range (S < 10). Using our experimental data, the fluxes of the various As species were estimated for the first time in estuarine waters. Inputs from the river were mainly constituted of particulate As (∼70%). Conversely, dissolved species were predominant in the net fluxes (∼65%) and As(III) accounted for ∼15% of the dissolved net flux. [ABSTRACT FROM AUTHOR]