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Reactivity of transparent exopolymeric particles: A key parameter of trace metal cycling in the lagoon of Nouméa, New Caledonia
Mari, X.; Migon, C.; Nicolas, E. (2009). Reactivity of transparent exopolymeric particles: A key parameter of trace metal cycling in the lagoon of Nouméa, New Caledonia. Mar. Pollut. Bull. 58(12): 1874-1879
In: Marine Pollution Bulletin. Macmillan: London. ISSN 0025-326X, more
Peer reviewed article  

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Keywords
    Coastal zone; Heavy metals; Hydrodynamics; Residence time; Trace metals; ISEW, New Caledonia [Marine Regions]; Marine

Authors  Top 
  • Mari, X.
  • Migon, C.
  • Nicolas, E.

Abstract
    Seawater samples were collected in the lagoon of Nouméa (southwest New Caledonia) along two transects from eutrophic coastal bays to the oligotrophic barrier reef. Land-based emissions to the lagoon were measured with dissolved and particulate concentrations of chromium (Cr) and nickel (Ni), used as tracers of both terrigenous and industrial (Ni ore treatment) activities, as well as dissolved and particulate concentrations of zinc (Zn), used as a tracer of urban effluents. The spatial variability of metal concentrations was related to geochemical and hydrodynamic conditions, i.e., respectively: (1) natural and anthropogenic emission sources, and chemical processes occurring in the water column; and (2) water residence times. The parameter used to describe the residence time of water masses was the local e-flushing time, i.e. the time required for a tracer mass contained within a given station to be reduced by a factor 1/e. High metal concentrations were found in coastal areas (up to 9000 ng dissolved Ni L−1), and steeply decreased with distance from the coast (down to 101 ng dissolved Ni L−1 near the barrier reef) to reach levels similar to those found in remote Pacific waters, suggesting a rapid renewal of waters close to the barrier. Distributions of metals in the lagoon are controlled upstream by land-based emission sources and later chemical processes. Then hydrodynamics constrain metal distributions, as shown by the observed relationship between local e-flushing times and the spatial variability of metal concentrations. In addition, a change in the direction of prevailing winds yielded a decrease of dissolved metal concentrations at the same site by a factor of 2.5 (Cr and Ni) and 2.9 (Zn). It is suggested that the residence time is a key parameter in the control of elemental concentrations in the lagoon waters, as much as land-based emission sources.

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