|The river Varde Ǻ: processes affecting the behaviour of metals and organochlorines during estuarine mixing|
Duinker, J.C.; Hillebrand, M.T.J.; Nolting, R.F.; Wellershaus, S.; Kingo Jacobsen, N. (1980). The river Varde Ǻ: processes affecting the behaviour of metals and organochlorines during estuarine mixing. Neth. J. Sea Res. 14(3-4): 237-267
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
|Authors|| || Top |
- Duinker, J.C.
- Hillebrand, M.T.J.
- Nolting, R.F.
- Wellershaus, S.
- Kingo Jacobsen, N.
Measurements of dissolved and suspended metals and organochlorine compounds were made in conjunction with hydrographic and sedimentological parameters at three fixed positions in different salinity regimes of the estuary of the Varde A at regular intervals during a tidal cycle and during a survey in the adjacent Wadden Sea in August 1976. In the river, low concentrations of dissolved pentachlorobenzene (0.1 ng.l-1), hexachlorobenzene (0.1 ng.l-1), polychlorinated biphenyls (1ng.l-1 Aroclor 1254 equivalent), α-hexachlorocyclohexane (2 ng.l-1), γ-hexachlorocyclohexane (2 ng.1-1) and a few yet unidentified compounds at similarly low concentrations were detected. In the estuary, the only compounds present in concentrations above the limits of detection in 1-litre samples were the hexachlorocyclohexane isomers. In all samples, the amount of each isomer in solution was larger than in suspension. No evidence was found for transitions of these compounds between solution and suspension during estuarine mixing. The metals Cd, Zn and Fe were removed from solution in the early stages of estuarine mixing by sorption to freshly eroded sediment particles in the mud reach. Conservative behaviour was found for Cu. Manganese is cycled between particulate and dissolved forms. It is removed from solution in the lower estuary and produced in the upper part, mainly in response to variations in pH and resuspended sediment concentration, resulting in a maximum in the dissolved Mn concentration at low salinities. Elemental contents in seston in the estuary were determined primarily by mixing of particles from the lower estuary, the river and resuspended bottom sediments. These have different contents of organic C, organic N and metals. The relative contribution from originally dissolved metals is small. The variations in elemental contents could be explained in terms of a model involving a continuously suspended fraction, dominating at low seston concentrations, consisting of smaller, less dense particles with relatively high contents of Cd, Zn, Cu, Pb, Ca, Mg, organic C and organic N, and a fraction introduced by resuspension, consisting of larger, denser particles with higher contents of Mn, Al and Ti. Elemental contents and elemental/Al ratios are nearly constant at seston concentrations above 20 mg.l-1. Elemental content of Fe and Si did not vary with seston concentration. It is suggested that in addition to Al silicates, other minerals such as Fe and Mn oxides and organic matter are important sites for particulate trace metals, especially in the continuously suspended fraction.