Publikationsdatum:
2022-05-26
Beschreibung:
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.
Beschreibung:
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.
Beschreibung:
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.
Schlagwort(e):
Flume
;
Harmful algal bloom
;
Heterocapsa triquetra
;
Phosphatic clay
;
Polyaluminum hydroxychloride
;
Resuspension
;
Sedimentation
Repository-Name:
Woods Hole Open Access Server
Materialart:
Preprint
Format:
271382 bytes
Format:
application/pdf
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