In order to obtain some fundamental data for maintenance of the coastal reclaimed site for disposal of various solid wastes, change of plankton population were investigated in relation to the change of water quality in a reclaimed site pond formed along the coastal line of Kitakyushu City, Japan. The pond water became rapidly brackish and polluted during seven years needed for the completion of the reclamation by disposing of the solid wastes.
The water quality in this pond was arranged in five clusters by use of one numerical classification method, agglomerative cluster analysis, which employs four water factors: pH, chlorinity, suspended solids, and COD on four seasons: February in winter, May in spring, August in summer, and November in autumn.
The occurrence pattern of dominant phytoplankton and five clusters of water quality were compared; it was found that the alternation between marine plankton and brackish-water plankton was observed around 10‰ in chlorinity, and fresh-water plankton began to appear below 5‰ in chlorinity. The marine plankton's highest COD value was 17mg/l, and fresh-and brakish water forms were able to occur as high as 40mg/l in COD. One species of a phototrophic bacterium was observed in one cluster which had abnormal conditions of 160mg/l in COD and 11.2 in pH.
These results revealed that there was an intimate relation between the characteristic occur-rence of plankton and water quality in each of the five clusters. The appearance of planktonic biota and the variation of water quality were affected by the climatic conditions, such as rises of temperature and copious rainfall.
