Particulate trace metal and major element distributions over consecutive tidal cycles in Port Jackson Estuary, Australia

Particulate trace metal (Cu, Cr, Ni, Pb and Zn) and major element (Fe, Mn and Al) concentrations have been determined following intensive sampling over two consecutive spring tidal cycles in the 'turbidity maximum zone' (TMZ) of the Port Jackson estuary, Australia. Salinity, temperature, pH, dissolved oxygen, suspended particulate matter (SPM) and chlorophyll a were also determined. A three-factor analysis of variance was used to test temporal variability in concentrations of particulate trace metals and major elements as a result of tidal oscillation. Estuarine master variables, such as temperature and pH, varied within a narrow range; nevertheless, the tidal signal was clear for surface and bottom waters. In surface water, no variance was detected in SPM concentrations between consecutive tidal cycles or between tidal stages (i.e. flood,.ebb and slack water). In bottom water, however, SPM concentrations were significantly higher (P less than or equal to 0.05) at flood tide than at slack high water and ebb tide. Concentrations of particulate trace metals and major elements in surface water do not display, significant. variability between tidal cycles or stages. Nevertheless, differences within each tidal stage were significant (P: 0.05) for all elements. In bottom water, only particulate Fe and Al exhibited significant differences (P : 0.05) between tidal cycles, whereas particulate Ni was the only trace element that presented significant differences (P less than or equal to 0.05) between tidal stages, following the distribution of SPM, with highest concentrations at flood tide. Among the metals studied, significant variation was found at all three temporal scales examined (i.e. from hours to consecutive tidal cycles), although the patterns of variation were different for each metal. The semi-diurnal fluctuation of SPM and particulate trace metal concentrations during spring tides is interpreted as a resuspension-deposition cycle caused by cyclical oscillations of bottom currents. The results are discussed in the context of the implications of tidal cycle influence on the geochemistry and cycling of particulate trace metals in the Port Jackson estuary.