Large scale rubber, oil palm and banana plantations have replaced pristine coastal ecosystems in Tiko, Cameroon, through which freshwater flows. Agrochemical inputs into aquatic systems have the potential to influence phytoplankton community structure through adjustment of physico-chemical characteristics of water. Since plantation establishment in Tiko, Cameroon, no studies on the impacts of the agro-chemicals used on the aquatic ecosystems have been carried out. Phytoplankton community structure was assessed to evaluate current status and existing physico-chemical conditions. Three streams flowing through the Tiko plantations were selected to evaluate these effects. Two sets of water samples were collected (10 cm below the surface) at each sampling point in triplicates for nutrient and phytoplankton analyses. Nitrate, bicarbonate, zinc, iron and turbidity were found to exceed the WHO and EPA water quality standards. Eighty (80) species of phytoplankton belonging to 10 divisions were recorded during the study. The division with the highest species abundance was Bacillariophyta (31 species) followed by Chlorophyta (21 species) and the most abundant species recorded was Microcystisaeruginosa followed by Chlorella sp.Phytoplankton richness and abundance were higher in streams that had higher concentrations of nitrates and phosphates. These happened to be flowing through plantations in which agrochemicals use and human activities were highest. Of the 80 species recorded, 27 were indicators of eutrophication. The saprobic index ranged from 0.19 - 1.00 indicating that the streams were eutrophic. The results are significant for better management and monitoring of these ecosystems.
Key words: Phytoplankton, community structure, nutrients, eutrophication, Tiko.