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Benthic-pelagic exchange of microalgae at a tidal flat: 1. Pigment analysis

Benthic-pelagic exchange of microalgae at a tidal flat: 1. Pigment analysis
Benthic-pelagic exchange of microalgae at a tidal flat: 1. Pigment analysis
Annular flume experiments and high-performance liquid chromatography (HPLC) were used to quantitatively and qualitatively measure benthic-pelagic exchange of microphytobenthos from natural sediments. Clear spatial and temporal differences in microphytobenthos resuspension in response to stepwise increases in current velocity were observed. Resuspension of chlorophyll a (chl a) from sandy sediments containing low levels of microphytobenthos biomass (<11.5 mg chl a m-2) occurred gradually and continuously over a range of current velocities from 10 to 40 cm s-1. In June, well-developed diatom mats at siltier sites (>56 mg chl a m-2) displayed strong resistance to erosion at currents <20 to 25 cm s-1, above which there was a very rapid increase in the amount of chl a in suspension following the stripping of the algal mat from the sediment surface. In September, when the diatom bloom was over, these sediments were less resistant to erosion and resuspension of microalgae occurred at current velocities above 15 to 20 cm-1. Site 1, situated at the edge of the flat, had a dense algal mat but low sediment stability. Microalgae were readily resuspended because the extracellular polymeric substances (EPS) produced by the migratory diatoms were unable to consolidate during the short emersion period. As a rule more chl a was resuspended from sandy sediments at current velocities 15 and 20 cm-1, but above this current velocity chl a resuspension was greater from silty sediments. Although sandy sites have low biomass in the surface layer, the greater depth of sediment erosion during bedload transport exposes more chl a to the surface. The percentage of sedimentary chl a lost at selected current velocities was estimated, and the implications for carbon supply to the pelagic and benthic systems discussed. Much of the biomass resuspended may be deposited locally, particularly in sandier regions. During the flume experiments it was observed that settling of fine sediment and microalgae was extremely rapid, because it was being biodeposited by suspension-feeding activity, and 'stripped' out of the water column by rapidly sinking suspended particulate matter (SPM). Qualitative changes in suspended material were measured as % chl a (chl a/phaeopigments ¥ 100%) and accessory pigment content. As current velocity increased the relative proportion of phaeopigments increased, which has important implications for benthic suspension feeders feeding in the benthic boundary layer. The findings from the flume experiments have been compared with in situ measurements of current velocity, SPM and chl a.
ALGAE, TIDAL FLATS, BENTHIC COMMUNITIES, PELAGIC ENVIRONMENT, PIGMENTS, SEDIMENTS, WESTERSCHELDE ESTUARY
0171-8630
59-73
Lucas, C.H.
521743e3-b250-4c6b-b084-780af697d6bf
Widdows, J.
bf510fc0-6c8d-4000-92eb-1bcd610a901d
Brinsley, M.D.
4b03d873-48c2-4a3b-9753-c0449cb02780
Salkeld, P.N.
8cfbdc49-ece8-4a64-b74c-58ed68e4eec1
Herman, P.M.J.
028ef873-bceb-44fb-9425-b47507b012d6
Lucas, C.H.
521743e3-b250-4c6b-b084-780af697d6bf
Widdows, J.
bf510fc0-6c8d-4000-92eb-1bcd610a901d
Brinsley, M.D.
4b03d873-48c2-4a3b-9753-c0449cb02780
Salkeld, P.N.
8cfbdc49-ece8-4a64-b74c-58ed68e4eec1
Herman, P.M.J.
028ef873-bceb-44fb-9425-b47507b012d6

Lucas, C.H., Widdows, J., Brinsley, M.D., Salkeld, P.N. and Herman, P.M.J. (2000) Benthic-pelagic exchange of microalgae at a tidal flat: 1. Pigment analysis. Marine Ecology Progress Series, 196, 59-73.

Record type: Article

Abstract

Annular flume experiments and high-performance liquid chromatography (HPLC) were used to quantitatively and qualitatively measure benthic-pelagic exchange of microphytobenthos from natural sediments. Clear spatial and temporal differences in microphytobenthos resuspension in response to stepwise increases in current velocity were observed. Resuspension of chlorophyll a (chl a) from sandy sediments containing low levels of microphytobenthos biomass (<11.5 mg chl a m-2) occurred gradually and continuously over a range of current velocities from 10 to 40 cm s-1. In June, well-developed diatom mats at siltier sites (>56 mg chl a m-2) displayed strong resistance to erosion at currents <20 to 25 cm s-1, above which there was a very rapid increase in the amount of chl a in suspension following the stripping of the algal mat from the sediment surface. In September, when the diatom bloom was over, these sediments were less resistant to erosion and resuspension of microalgae occurred at current velocities above 15 to 20 cm-1. Site 1, situated at the edge of the flat, had a dense algal mat but low sediment stability. Microalgae were readily resuspended because the extracellular polymeric substances (EPS) produced by the migratory diatoms were unable to consolidate during the short emersion period. As a rule more chl a was resuspended from sandy sediments at current velocities 15 and 20 cm-1, but above this current velocity chl a resuspension was greater from silty sediments. Although sandy sites have low biomass in the surface layer, the greater depth of sediment erosion during bedload transport exposes more chl a to the surface. The percentage of sedimentary chl a lost at selected current velocities was estimated, and the implications for carbon supply to the pelagic and benthic systems discussed. Much of the biomass resuspended may be deposited locally, particularly in sandier regions. During the flume experiments it was observed that settling of fine sediment and microalgae was extremely rapid, because it was being biodeposited by suspension-feeding activity, and 'stripped' out of the water column by rapidly sinking suspended particulate matter (SPM). Qualitative changes in suspended material were measured as % chl a (chl a/phaeopigments ¥ 100%) and accessory pigment content. As current velocity increased the relative proportion of phaeopigments increased, which has important implications for benthic suspension feeders feeding in the benthic boundary layer. The findings from the flume experiments have been compared with in situ measurements of current velocity, SPM and chl a.

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More information

Published date: 2000
Keywords: ALGAE, TIDAL FLATS, BENTHIC COMMUNITIES, PELAGIC ENVIRONMENT, PIGMENTS, SEDIMENTS, WESTERSCHELDE ESTUARY

Identifiers

Local EPrints ID: 8708
URI: https://eprints.soton.ac.uk/id/eprint/8708
ISSN: 0171-8630
PURE UUID: 322cc044-2640-4e59-8658-13990a7cbbd5
ORCID for C.H. Lucas: ORCID iD orcid.org/0000-0002-5929-7481

Catalogue record

Date deposited: 25 Aug 2004
Last modified: 06 Jun 2018 13:07

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