Phytoplankton community structure in relation to physico-chemical factors in a tropical soda lake, Lake Shala (Ethiopia)

Abstract

Phytoplankton communities responses to physico-chemical factors were studied in Lake Shala from January to December 2018. Distinct spatial and seasonal variations were observed for all physico-chemical parameters, except DO (ANOVA: p < 0.05). In total, 72 taxa, Bacillariophyta (55 taxa), Chlorophyta (seven taxa), Cyanobacteria (six taxa), Euglenophyta (two taxa), Dinophyta (one taxon) and Charophyta (one taxon) were identified. Phytoplankton abundance and biomass ranged from 5 789.3 cells ml^–1 to 1 516.2 cells ml^–1, with a mean of 8 756.9 cells ml^–1 and 9.8 μg l⁻¹ to 25.8 μg l⁻¹, with a mean of 17.1 μg l⁻¹, respectively, and showed seasonal variations (p < 0.05). Based on RDA analysis, most species were abundant in Shala Gike Shore station. Their distribution was negatively correlated with salinity and EC, whereas pH, alkalinity, NO₃–N, SRP, TP, NH₃–N and SiO₂ had a positive correlation. Previously Lake Shala was dominated by Cryptophyta but this has switched to a diatom-dominant community. Such changes in phytoplankton taxa may be suggestive of ecological change. This study provides baseline data on the phytoplankton community structure of Lake Shala associated with physico-chemical changes, against which future community structure can be evaluated.