Using clay to control harmful algal blooms : deposition and resuspension of clay/algal flocs

dc.contributor.author Beaulieu, Stace E.
dc.contributor.author Sengco, Mario R.
dc.contributor.author Anderson, Donald M.
dc.date.accessioned 2006-03-14T18:32:21Z
dc.date.available 2006-03-14T18:32:21Z
dc.date.issued 2003-12-21
dc.description Author Posting. © Elsevier B.V, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V for personal use, not for redistribution. The definitive version was published in Harmful Algae 4 (2005): 123-138, doi:10.1016/j.hal.2003.12.008. en
dc.description.abstract Harmful algal blooms (HABs) may be legitimate targets for direct control or mitigation, due to their impacts on commercial fisheries and public health. One promising control strategy is the rapid sedimentation of HABs through flocculation with clay. The objective of this study was to evaluate flow environments in which such a control strategy might be effective in removing harmful algae from the water column and depositing a layer of clay/algal flocs on the sea floor. We simulated the natural environment in two laboratory flumes: a straight-channel “17-m flume” in which flocs settled in a still water column and a “racetrack flume” in which flocs settled in flow. The 17-m flume experiments were designed to estimate the critical bed shear stress for resuspension of flocs that had settled for different time periods. The racetrack flume experiments were designed to examine the deposition and repeated resuspension of flocs in a system with tidal increases in flow speed. All flume runs were conducted with the non-toxic dinoflagellate Heterocapsa triquetra and phosphatic clay (IMC-P4). We repeated the experiments with a coagulant, polyaluminum hydroxychloride (PAC), expected to enhance the removal efficiency of the clay. Our experiments indicated that at low flow speeds (≤ 10 cm s-1), phosphatic clay was effective at removing algal cells from the water column, even after repeated resuspension. Once a layer of flocs accumulated on the bed, the consolidation, or dewatering, of the layer over time increased the critical shear stress for resuspension (i.e. decreased erodibility). Resuspension of a 2-mm thick layer that settled for 3 hours in relatively low flow speeds (≤ 3 cm s-1) would be expected at bed shear stress of ~0.06-0.07 Pa, as compared to up to 0.09 Pa for a layer that was undisturbed for 9 or 24 hours. For the same experimental conditions, the addition of PAC decreased the removal efficiency of algal cells in flow and increased the erodibility of flocs from the bottom. By increasing the likelihood that flocs remain in suspension, the addition of PAC in field trials of clay dispersal might have greater impact on sensitive, filter-feeding organisms. Overall, our experiments suggest that the flow environment should be considered before using clay as a control strategy for HABs in coastal waters. en
dc.description.sponsorship This project was funded by the Florida Institute of Phosphate Research (Grant # 99-03-138), with facilities provided by the Rinehart Coastal Research Center at WHOI. en
dc.format.extent 271382 bytes
dc.format.mimetype application/pdf
dc.identifier.uri https://hdl.handle.net/1912/662
dc.language.iso en_US en
dc.relation.uri https://doi.org/10.1016/j.hal.2003.12.008
dc.subject Flume en
dc.subject Harmful algal bloom en
dc.subject Heterocapsa triquetra en
dc.subject Phosphatic clay en
dc.subject Polyaluminum hydroxychloride en
dc.subject Resuspension en
dc.subject Sedimentation en
dc.title Using clay to control harmful algal blooms : deposition and resuspension of clay/algal flocs en
dc.type Preprint en
dspace.entity.type Publication
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relation.isAuthorOfPublication 155b043c-bfe0-46cc-83a5-64e99bc3ff41
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relation.isAuthorOfPublication.latestForDiscovery 15c62862-8e1f-4880-9388-ba91cd797e9a
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