Dissolved trace metals in the estuarine plumes of the Humber, Thames and Rhine rivers

Abstract

Estuarine plumes, the coastal sea areas directly influenced by a riverine freshwater discharge, form an important transition zone in the journey of land-derived trace metals to the oceanic sink, connecting river and estuarine environments with the continental shelf and eventually the deep sea, and modifying the flux of material from the coastal margins to the world ocean. The work described in this thesis was undertaken as part of the North Sea Project (NSP) of the Natural Research Council (NERC) of the United Kingdom. Within the wider framework of this program, five twelve-day cruises were dedicated to the survey of the estuarine plumes of the Humber, Thames and Rhine rivers at different times of the year. Dissolved and particulate trace metal samples were taken and analysed, together with salinity, turbidity, chlorophyll, nutrients and several other relevant parameters, in order to establish trace metal distributions throughout the survey areas and between the dissolved and particulate phases, and to investigate influx from estuaries and the atmosphere and exports to the central shelf sea as well as seasonal patterns and biological and sedimentary mobilisation and removal mechanisms. Manganese and cobalt were found to be rapidly removed from the dissolved phase in the vicinity of the outflows, but were also remobilised in estuaries, during resuspension events and in offshore areas during the summer months. Dissolved lead concentrations were generally lower in turbid nearshore areas off the Humber and Rhine rivers than offshore, resulting in positive correlations with salinity in the plumes. Iron was found to be the element strongest attached to particles. In the few cases of apparent linear mixing, especially in estuaries, the following effective riverine end member concentrations were found: 90-10000 nmol/1 for Mn (including remobilisation in the low salinity zone), 350 nmol/1 for Fe, 4.8-32 nmol/1 for Co and 0.7-20 nmol/1 for Pb. Compared to world wide average river concentrations, the estimates show highly elevated levels for all elements except Mn and Fe: by one order of magnitude for Ni, Co and Cu, and by up to two orders of magnitude for Zn, Cd and Pb. This differentiation between the metals is consistent with a high anthropogenic contribution to the elevated levels. The river Thames was found to be a very strong source of dissolved lead (up to 20 nmol/1), whilst the Humber was shown to be a significant source of cadmium (up to 9.3 nmol/1). Point sources of cadmium were also found both in the Rhine estuary and the adjacent coastal zone.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata