Abstract

Phytoplankton is very sensitive to nutrient changes. Very little work has been carried out on the effect of these changes on the phytoplankton community in the Ndop wetland. Four paddy-field sites were studied to evaluate the effect of some abiotic factors on their occurrence and abundance of phytoplankton. Water samples were collected from the paddy-fields sites following age gradient 34, 32, 22 and 5 years old fields. Potassium, sodium, nitrate-nitrogen, phosphate-phosphorus, conductivity and pH were the factors that contributed to phytoplankton diversity and density. There was a positive significant correlation between pH and potassium (r = 0.99, P ≤ 0.01), and pH and sodium (r = 0.977, P ≤ 0.05). A negative correlation (r = -0.992, P ≤ 0.01) was observed between pH and evenness. Eight divisions of phytoplankton were recorded: Chlorophyta (26.42%), Bacillariophyta (20.76%), Pyrrhophyta (20.76%), Cyanophyta (15.09%), Chrysophyta (1.87%), Xanthophyta (3.77%), Rhodophyta (1.87%), and Euglenophyta (7.55%). The most abundant species included Microcystis aeruginosa, Anacystis sp., Chlorococcus dispersesand Peridinum sp. These may be used as bioindicator of the water quality. Diversity index increased with increase in the age of paddy-fields sites. 43% of the species indicated eutrophic status, 16.9% mesotrophic, and 20.8% oligotrophic. Eutrophic species were more in the older paddy sites while the young paddy sites had more oligotrophic species.

Key words: Phytoplankton, diversity, abundance, pollution, Ndop wetland