Cycling of trace metals in coastal waters : biogeochemical processes involving suspended particles
Cycling of trace metals in coastal waters : biogeochemical processes involving suspended particles
Recent investigations have shown that suspended particles exert a significant influence on the distribution and biogeochemical cycling of trace metals in seawater. These processes are particularly important in temperate coastal waters, characterised by elevated phytoplankton activity during the spring period. In order to investigate the effect of suspended particles, particularly those of biogenic origin, on the biogeochemical cycling of Fe, Mn, Cu, Co, Ni, Cd, Zn and Pb in coastal waters, dissolved and particulate trace metal samples (suspended and settling), together with salinity, nutrients, total particulate carbon and other related data were collected during 19 cruises aboard RV Calanus between March, 1991 and February, 1992 in Loch Linnhe; a silled fjord on the west coast of Scotland. Particulate trace metal samples were also collected on a single cruise (CH72, October 1990) in the extended estuarine plume of the River Rhine as part of the Rhine Outflow Experiment.
Analytical techniques for the analysis of particulate material were developed. These include weak acid leaches of the environmentally available metal fraction and strong acid digestion, utilising microwave heating, to liberate the metals associated with the refractory mineral phases.
Electron microscopy of suspended sediment samples showed the spring phytoplankton bloom comprised the diatoms Skeletonema costatum and Thallassiosira sp. Particulate Cd and leachable-P showed increasing levels coincident with the onset of the bloom. Phosphorus was rapidly recycled after the bloom crash while Cd concentrations continued to increase in particles, reaching a maximum of 6.33 nmol g-1, an enrichment relative to the winter particle population of ∼8.5. The difference in the peak of recycling of Cd relative to P was greater than 8 days but less than 15 days and suggests that in contrast to the deep ocean, Cd and P are decoupled in the coastal environment. A substantial amount (∼44% ) of the total annual flux of Mn to the sediments was recycled. The estimated recyling flux was found to have a strong seasonal pattern, with little or no Mn recycling prior to the spring phytoplankton blooms and increasing value after the bloom crash, reaching a maximum of 348 μmol m^-1 day^-1 in late autumn. Levels then decreased, attaining pre-bloom levels early in the following year. This cycle suggests that bacterial decay of deposited organic carbon associated with the spring bloom maintained reducing conditions in the sediments throughout most of the year. Surface sediments were sufficiently oxic to prevent the release of reduced Mn for only a brief period prior to the spring bloom.
University of Southampton
1993
Hall, Ian Robert
(1993)
Cycling of trace metals in coastal waters : biogeochemical processes involving suspended particles.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Recent investigations have shown that suspended particles exert a significant influence on the distribution and biogeochemical cycling of trace metals in seawater. These processes are particularly important in temperate coastal waters, characterised by elevated phytoplankton activity during the spring period. In order to investigate the effect of suspended particles, particularly those of biogenic origin, on the biogeochemical cycling of Fe, Mn, Cu, Co, Ni, Cd, Zn and Pb in coastal waters, dissolved and particulate trace metal samples (suspended and settling), together with salinity, nutrients, total particulate carbon and other related data were collected during 19 cruises aboard RV Calanus between March, 1991 and February, 1992 in Loch Linnhe; a silled fjord on the west coast of Scotland. Particulate trace metal samples were also collected on a single cruise (CH72, October 1990) in the extended estuarine plume of the River Rhine as part of the Rhine Outflow Experiment.
Analytical techniques for the analysis of particulate material were developed. These include weak acid leaches of the environmentally available metal fraction and strong acid digestion, utilising microwave heating, to liberate the metals associated with the refractory mineral phases.
Electron microscopy of suspended sediment samples showed the spring phytoplankton bloom comprised the diatoms Skeletonema costatum and Thallassiosira sp. Particulate Cd and leachable-P showed increasing levels coincident with the onset of the bloom. Phosphorus was rapidly recycled after the bloom crash while Cd concentrations continued to increase in particles, reaching a maximum of 6.33 nmol g-1, an enrichment relative to the winter particle population of ∼8.5. The difference in the peak of recycling of Cd relative to P was greater than 8 days but less than 15 days and suggests that in contrast to the deep ocean, Cd and P are decoupled in the coastal environment. A substantial amount (∼44% ) of the total annual flux of Mn to the sediments was recycled. The estimated recyling flux was found to have a strong seasonal pattern, with little or no Mn recycling prior to the spring phytoplankton blooms and increasing value after the bloom crash, reaching a maximum of 348 μmol m^-1 day^-1 in late autumn. Levels then decreased, attaining pre-bloom levels early in the following year. This cycle suggests that bacterial decay of deposited organic carbon associated with the spring bloom maintained reducing conditions in the sediments throughout most of the year. Surface sediments were sufficiently oxic to prevent the release of reduced Mn for only a brief period prior to the spring bloom.
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Published date: 1993
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Local EPrints ID: 462272
URI: http://eprints.soton.ac.uk/id/eprint/462272
PURE UUID: 50723f36-9f50-4b07-91d7-daebd3861b02
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Date deposited: 04 Jul 2022 19:04
Last modified: 04 Jul 2022 19:04
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Author:
Ian Robert Hall
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