Vertical gradients for particulate Cu fractions in estuarine water over tidal flats

L.J.A. Gerringa, H. Hummel, T.C.W. Moerdijk-Poortvliet

    Onderzoeksoutput: Bijdrage aan wetenschappelijk tijdschrift/periodieke uitgaveArtikelWetenschappelijkpeer review


    The speciation of particulate copper was determined at several depths (0, 5 and 15 cm above the sediment surface) in the water column above intertidal flat systems in the polluted estuary Westerschelde (WS) and the relatively un-polluted Oosterschelde sea-arm (OS), in order to assess differences in water quality between the main body of water routinely determined in monitoring programmes and that at the sediment-water interface which is factually interacting with the benthic organisms. The bioavailable fraction was estimated by two sequential extraction's: a pH=5 acetic acid (Ac) and a pH=8 Na- dodecylsulphate (Dod) extraction. Irrespective the different character of the systems, when the differences in salinity were taken into account, dissolved fractions (DOC, pH) differed hardly between seasons and stations. Although occasionally a quantitative differentiation between sampling depths could occur, with higher particulate concentrations (Cu, Ac-Cu, Dod- Cu, C, sediment, POC, chlorophyll a) near the sediment-water interface, the qualitative properties (Cu/POC, Ac-Cu/POC, Dod- Cu/POC, Chl-a/POC, C/N) of the water remained constant all over the tidal cycle and between depths. The measurements carried out during monitoring programmes in main water streams thus result in a strong under-estimation of the quantities of particulate substances (seston, POC, chlorophyll a, Cu) available to the benthos at intertidal flats, whereas the qualitative (relative) properties are correctly estimated. With regard to the interaction with benthic organisms, it is concluded that the unexpected levels of Cu in the clam Macoma balthica (equal or higher in the OS than in the polluted Westerschelde) are partly caused by differences in sediment Cu concentrations (Hummel et al., 1997). Additionally the low concentration of suitable, chlorophyll a related, food in OS force the clam to filtrate at higher rates, whereby a higher volume of water and thus ultimately an equal or higher amount of Cu, will be taken in. [KEYWORDS: copper; speciation; estuary; bioavailability particulate organic carbon; bivalve Macoma-balthica mollusca; dutch wadden sea; scheldt estuary; trace-metals; organic-carbon; food-intake; netherlands; sediment; copper; matter]
    Originele taal-2Engels
    Pagina's (van-tot)149-162
    StatusGepubliceerd - 1999


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