A seasonal study on phytoplankton diversity and dynamics of Lake Chamo, Ethiopia

Phytoplankton succession in open lakes depends on the availability of nutrients, temperature, light intensity and transparency. Phytoplankton communities usually undergo a fairly predictable annual cycle, but some species may grow exponentially forming the blooms. Accordingly, the seasonal diversity and dynamics of phytoplankton and their correlation with environmental factors were investigated in Lake Chamo, from December, 2013 to November, 2014. Samples were taken from four different sites of the lake; each of these sampling sites had their own unique characteristics. Seasonal plankton samples were collected using nylobolt plankton net (No. 25). pH, water temperature, specific conductivity, saturation, total dissolved solids, salinity and dissolved oxygen were measured in the field. The results showed that there is significant difference in the mean value of pH across the different seasons at the first sampling site, season II having significantly higher value than season I and IV. Water temperature also significantly varied among sampling sites and seasons, site 3 in spring 2014 having significantly higher value (30.4 +/- 0.21 degrees C) than site 2 during summer 2014 (26.0 +/- 0.12 degrees C). Cyanophyta, Chlorophyta and Bacillariophyta accounted 96% of the total phytoplankton abundance during the study period. Pediastrum, Scendesmus and Closterium species were the predominant Chlorophyta, during the rainy seasons. The average Cyanophyta count was positively and non-significantly correlated with water temperature and turbidity of the lake. Overall, the four seasons exhibit different phytoplankton species composition across different sites. The diversity was high during winter season in all sampling sites.