Removal of Cochlodinium polykrikoides by dredged sediment: A field study

A 2-year field study was conducted in November 2006 at Haejin and September 2007 at Namhae, South Korea to exterminate harmful bloom, Cochlodinium polykrikoides, by sediment-based materials. Slaked lime, quicklime and an aluminum sludge were mixed with sediment for the Haejin field. Bentonite, zeolite and quicklime were mixed with sediment for the Namhae field. Before and after sediment spray, seawater samples were collected at three depths (surface, middle and bottom) at each site and the characteristics (pH, temperature and salinity) were monitored. All samples were fixed immediately with Lugol's solution for cell counting. The results showed no changes in pH, temperature and salinity of seawater after spraying of the materials but rapidly reduced seawater turbidity due to the settling of sediment particles. The C. ploykrikoides cell density decreased rapidly according with elapsed time after the spraying of all sediment-based materials. No significant differences in the percent removal efficiency were found across the sediment materials. However, this study clearly indicated that the removal efficiency of the C. polykrikoides depended on the initial cell density. The above results indicate that sediment could be effective for red tide control.