Using clay to control harmful algal blooms : deposition and resuspension of clay/algal flocs
Beaulieu, Stace E.
Sengco, Mario R.
Anderson, Donald M.
MetadataShow full item record
KeywordFlume; Harmful algal bloom; Heterocapsa triquetra; Phosphatic clay; Polyaluminum hydroxychloride; Resuspension; Sedimentation
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.
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.
Showing items related by title, author, creator and subject.
Alexandrium fundyense cysts in the Gulf of Maine : long-term time series of abundance and distribution, and linkages to past and future blooms Anderson, Donald M.; Keafer, Bruce A.; Kleindinst, Judith L.; McGillicuddy, Dennis J.; Martin, Jennifer L.; Norton, Kerry; Pilskaln, Cynthia H.; Smith, Juliette L.; Sherwood, Christopher R.; Butman, Bradford (2013-10)Here we document Alexandrium fundyense cyst abundance and distribution patterns over nine years (1997 and 2004-2011) in the coastal waters of the Gulf of Maine (GOM) and identify linkages between those patterns and several ...
Investigating the importance of sediment resuspension in Alexandrium fundyense cyst population dynamics in the Gulf of Maine Butman, Bradford; Aretxabaleta, Alfredo L.; Dickhudt, Patrick J.; Dalyander, P. Soupy; Sherwood, Christopher R.; Anderson, Donald M.; Keafer, Bruce A.; Signell, Richard P. (Elsevier, 2013-11-05)Cysts of Alexandrium fundyense, a dinoflagellate that causes toxic algal blooms in the Gulf of Maine, spend the winter as dormant cells in the upper layer of bottom sediment or the bottom nepheloid layer and germinate in ...
Insights into the loss factors of phytoplankton blooms : the role of cell mortality in the decline of two inshore Alexandrium blooms Choi, Chang Jae; Brosnahan, Michael L.; Sehein, Taylor R.; Anderson, Donald M.; Erdner, Deana L. (2017-01)While considerable effort has been devoted to understanding the factors regulating the development of phytoplankton blooms, the mechanisms leading to bloom decline and termination have received less attention. Grazing ...