A proposal for the use of sediment removed when dredging is adopted to control cyanobacterial bloom formation

Abstract

Heavy cyanobacterial blooms have formed in recent years in Hirosawa-no-ike Pond (Kyoto, Japan). Although the pond water is drained during winter and the sediment is exposed to air for over two months, cyanobacterial blooms appear annually each summer. Moreover, the dominance of Microcystis aeruginosa during the summer months cannot be accounted for solely by cell division. These findings suggest that colonies and resting spores of cyanobacteria in the sediment play a critical role as seed populations for blooms. Numerous colonies of Microcystis species are present in the top layers of the sediment with a water content of over 40 % during winter. Accordingly, the formation of cyanobacterial blooms may be controllable by removing the top layers of the sediment containing the inocula of bloom-forming cyanobacteria. To examine the effectiveness of the removed sediment in crop cultivation, 20 crops were cultured using the sediment from March 2006 to April 2007. Culturing with the removed sediment substantially increased the final yields of ten crops. These results suggest that sediment removal may not only be effective in controlling the development of cyanobacterial blooms, but also in increasing the yields of many crops.